This book explains how with careful planning and design, the functions and performance of constructed wetlands can provi
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Constructed Wetlands for Water Quality Improvement is a virtual encyclopedia of state-of-the-art information on the use
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Over the past decades, the world has seen a dramatic increase in inequality. To what extent have the rules that govern t
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Sustainable development is one of the key challenges of our time. It has social, ecological and economic dimensions, whi
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The educational manual is developed in accordance with the standard program of the discipline «Environment and sustainab
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Promoting sustainable production and consumption is at the core of sustainable development, which depends on achieving l
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This book deals with the main challenges of sustainable development and the role of sustainable business and corporate s
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Subsidies are pervasive in OECD countries and are among the most powerful public policy instruments. But they often int
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Constructed Wetlands and Sustainable Development This book explains how, with careful planning and design, the functions and performance of constructed wetlands can provide a huge range of beneﬁts to humans and the environment. It documents the current designs and speciﬁcations for free water surface wetlands, horizontal and vertical subsurface ﬂow wetlands, hybrid wetlands and bioretention basins; and explores how to plan, engineer, design and monitor these natural systems. Sections address resource management (landscape planning), technical issues (environmental engineering and botany), recreation and physical design (landscape architecture) and biological systems (ecology). Site and municipal scale strategies for ﬂood management, stormwater treatment and green infrastructure are illustrated with case studies from the USA, Europe and China, which show how these principles have been put into practice. Written for upper-level students and practitioners, this highly illustrated book provides designers with the tools they need to ensure constructed wetlands are sustainably created and well-managed. Gary Austin is the author of Green Infrastructure for Landscape Planning (Routledge 2014). He is a landscape architect who studied under John Lyle and taught at the California State Polytechnic University, Pomona, USA. He has practised in the public and private sectors and has taught landscape architecture at the University of Washington, USA, and the University of Idaho, USA. His teaching and research focus on community revitalization, urban biological diversity and treatment of wastewater and stormwater for water quality improvement. Kongjian Yu is co-author of the inﬂuential book The Art of Survival (2007). He is Visiting Professor of Landscape Architecture at Harvard University, USA, and the principal of Turenscape, a large landscape architecture ﬁrm in China. The many constructed and monitored wetland projects that his ﬁrm has designed appear in this book. He is also Professor and Dean at Beijing University, China.
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Constructed Wetlands and Sustainable Development Gary Austin and Kongjian Yu
First published 2016 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN and by Routledge 711 Third Avenue, New York, NY 10017 Routledge is an imprint of the Taylor & Francis Group, an informa business © 2016 Gary Austin and Kongjian Yu The right of Gary Austin and Kongjian Yu to be identiﬁed as authors of this work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identiﬁcation and explanation without intent to infringe. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data Names: Austin, Gary (Gary D.), author. | Yu, Kongjian, author. Title: Constructed wetlands and sustainable development / Gary Austin and Kongjian Yu. Description: Abingdon, Oxon ; New York, NY : Routledge, 2016. | Includes bibliographical references and index. Identiﬁers: LCCN 2016003285| ISBN 9781138908987 (hardback : alk. paper) | ISBN 9781138908994 (pbk. : alk. paper) | ISBN 9781315694221 (ebook) Subjects: LCSH: Constructed wetlands. | Water—Pollution. | Ecological engineering. Classiﬁcation: LCC TD756.5 .A97 2016 | DDC 628.3/5—dc23 LC record available at https://lccn.loc.gov/2016003285 ISBN: 978-1-138-90898-7 (hbk) ISBN: 978-1-138-90899-4 (pbk) ISBN: 978-1-315-69422-1 (ebk) Typeset in Sabon by Florence Production Ltd, Stoodleigh, Devon, UK
Contents List of ﬁgures List of tables Acknowledgements
vi xiv xvi
Water and sustainable urban design
Characteristics of wastewater
Free water surface constructed wetlands
Horizontal subsurface ﬂow treatment wetlands
Vertical subsurface ﬂow constructed wetlands
Hybrid constructed wetlands
Plants in constructed wetlands
Stormwater management and sustainable development
Increasing the sustainability of agriculture
Treatment of industrial efﬂuent in constructed wetlands
Appendix A Appendix B Appendix C Index
269 271 272 279
Figures 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 2.1 2.2 3.1 3.2
Philadelphia’s campaign to divert stormwater run-off into inﬁltration areas Flooding risk in three categories and outstanding habitat and cultural features Flow direction for stormwater through the three corridor types The use of swales and basins in the narrowest and most urban corridors Surface drainage system in a secondary corridor The widest corridors featuring the best biological diversity Intersection between one of the widest corridors and an intermediate one One of the widest corridors supporting signiﬁcant habitat Intermediate corridor at Wulijie Variety in the visual character and diverse treatment strategies within the intermediate wetland corridors The narrowest corridor is the most urban but sufﬁciently wide to provide privacy and light The controlling plan for a small section of the new town of Wulijie Artist’s rendering of the proposed development of Wulijie Primary and intermediate corridors meet in Wulijie The use of spray Irrigation A stormwater outfall pipe Map showing precipitation trends in the United States from 1958 to 2007 The principal aquifers in the United States Fire on the Cuyahoga River in 1952 The city of Roseburg, Oregon’s 350-acre restored wetland and land application of efﬂuent Map showing the conditions of rivers and streams in the United States based on the presence and health of biological indicators Mine tailing pollution of a small stream Algae caused by excess nutrients from agricultural and domestic wastewater Free water surface wetland treating stormwater in Wulijie, China Horizontal subsurface ﬂow wetland in Casper, Wyoming E. coli bacteria colonies in a culture dish BOD tests of wastewater samples Conventional wastewater treatment plant using a large pump powering an aeration device Blue Heron Water Reclamation Facility, Titusville, Florida Free water surface wetland mimicking natural wetlands
2 3 3 4 4 5 5 5 6 6 6 7 8 8 10 11 12 13 17 18 18 20 20 22 23 23 27 29 31 32
3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10
Inﬂow from the wastewater treatment plant at Blue Heron water Reclamation Facility, Titusville, Florida Wastewater inﬂow being aerated Design of a free water surface wetland Differing water depths encouraging a variety of species to ﬂourish Below ground view of a wetland cell outlet trench Plan view diagram of the constructed wetland sequence at National Cheng-Kung University E L Huie Jr Constructed Treatment Wetlands, Clayton County, Georgia Free water surface constructed wetland in Albany, Oregon Talking Waters Garden, Albany, Oregon Deep water zones at the Talking Water Gardens, Albany, Oregon Panoramic view of the treatment wetland at the Talking Water Gardens, Oregon The aeration process at the Talking Water Gardens, Albany, Oregon Wapato in the Talking Water Gardens, Albany, Oregon Plant varieties at the Boone Presbyterian Church stormwater treatment wetland, North Carolina The horizontal subsurface ﬂow wastewater treatment wetland, Krovi, Czech Republic Coarse gravel inlet trench and ﬁlter bed for a horizontal subsurface ﬂow wetland Example of a horizontal subsurface ﬂow wetland Horizontal subsurface ﬂow wetland under construction Comparison of distribution and collection piping Gravel media in horizontal subsurface ﬂow constructed wetlands Aerial view of a trench horizontal subsurface ﬂow wetland under construction Model of linear horizontal subsurface ﬂow wetland First wedge of coarse stone Horizontal subsurface ﬂow trench capped with a layer of ﬁne gravel and a top layer of sand Horizontal subsurface ﬂow wetland and elevated efﬂuent storage tank Vertical subsurface ﬂow wetland, Silkerode, Germany Vertical subsurface ﬂow wetland based on Danish standards Vaults and piping system for a vertical subsurface ﬂow wetland Vertical ﬂow subsurface wetland during testing and construction Two-stage French system used for vertical ﬂow treatment wetlands Achieving an aerobic environment for bacteria Vertical subsurface ﬂow wetland in Jiangxiang, China Liner, drainage piping and ﬁlter media for a vertical subsurface ﬂow wetland Vertical ﬂow subsurface wetland planted with yellow ﬂag (Iris pseudacorus) Stand of Papyrus is in a vertical ﬂow treatment wetland in Peru
33 33 34 36 37 38 40 41 42 42 43 44 46 48 51 52 54 57 58 59 61 62 63 63 64 71 72 72 73 74 75 77 78 79 80
5.11 5.12 5.13 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 7.25 7.26 7.27 7.28 7.29 7.30 7.31
Section of two-stage vertical subsurface ﬂow wetland Installation of waterproof membrane and drainage system of a vertical subsurface ﬂow cell Vertical ﬂow wetland, Shengyang, China Experimental wastewater facility near Carrión de los Céspedes, Spain Vertical subsurface ﬂow wetland stage with Phragmites Second stage (horizontal subsurface ﬂow) of the hybrid treatment Free water treatment stage covered by a variety of plant species Storage tank Hybrid wetland, Hennersdorf, Germany Hybrid wetland and central park, Koh Phi Phi, Thailand, Aesthetics of wetland and ecotourism resort, Lake Yangcheng Three stages of vertical subsurface ﬂow wetland, Shenyang, China Treated efﬂuent from the three vertical subsurface ﬂow beds Example of planting design by Turenscape, Tianjin, China Free water surface wetland treats polluted river water and stormwater and creates biodiversity niches Aggressive plant species dominating wetland Plant diversity and aesthetic quality, Houtan Park, Shanghai Full range of wetland plants Plant zones in a constructed wetland Plan representing the installed planting design for a stormwater wetland Typha latifolia (Broadleaf cattail) Typha angustifolia Phragmites australis harvesting Phragmites australis seed plumes Example of species attracted to wetlands by Phragmites australis Phragmites australis in dense single species stands Juncus effusus Side view of the Juncus effusus inﬂorescence Eleocharis quadrangulata (Squareside Spikerush) Eleocharis acicularis (Needle Spikerush) Eleocharis palustris (Common Spikerush) Eleocharis sphacelata (Tall Spikerush) Eleocharis dulcis (Chinese Water Chestnut) Phalaris arundinacea Phalaris arundinacea as a hybrid Scirpus californicus Scirpus validus (River Clubrush) Scirpus maritimus Carex riparia Carex nebrascensis (Nebraska Sedge) Carex stipata (Awl-Fruit Sedge) Iris pseudacorus (Yellow Flag Iris) Sagittaria latifolia (Common Arrowhead) Sagittaria latifolia
81 85 85 89 90 91 92 93 94 95 96 96 97 99 99 100 101 101 101 103 104 104 106 107 108 108 109 109 110 111 111 112 113 113 113 114 115 116 117 117 117 119 120 120
7.32 7.33 7.34 7.35 7.36 7.37 7.38 7.39 7.40 7.41 7.42 7.43 7.44 7.45 7.46 7.47 7.48 7.49 7.50 7.51 7.52 7.53 7.54 7.55 7.56 7.57 7.58 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15
Pontederia cordata (Pickerel Weed) Caltha palustris (Marsh Marigold) Two Canna hybrid varieties within a shopping area wetland Canna indica Canna indica’s long ﬁbrous roots Canna ﬂaccida Canna ﬂaccida in Florida Cyperus papyrus A Laysan Albatross nestled in Cyperus involucratus on Sand Island, Midway Atoll New Cyperus papyrus shoots being removed to be replanted Arundo donax Thalia dealbata Thalia geniculata Zantedeschia aethiopica Heliconia psittacorum Acorus gramineus (Japanese Sweet Flag) Agapanthus The exotic ﬂowers of the bird of paradise Watsonia borbonica Hymenocallis littoralis Bacopa Monnieri (Water Hyssop) Colocasia esculenta Eichhornia crassipes Water hyacinth ﬂower and foliage Pistia stratiotes (Water Lettuce) Lemna minor (Duckweed) High plant diversity with species organized in masses and according to water depth and frequency of inundation The Sanlihe River restoration project The Sanlihe River restoration project, restored river Proposed changes to the Arroyo Secco River Channel The Isar River, Munich, Germany Natural riparian vegetation Riparian wetlands along and within rivers and streams Wetlands along the Kobuk River, Alaska Efforts are underway to restore portions of the Los Angeles River Constructed wetland along the Tanghe River Huangpu River upstream from Shanghai Coal-ﬁred energy and industrial plants along the Huangpu River Aerial view of Houtan Park along the bank of the Huangpu River near the centre of Shanghai Houtan Park along the bank of the Huangpu River near the centre of Shanghai The industrial riverbank of the Huangpu River at the proposed location of Houtan Park The Chinese Pavilion at the 2010 Shanghai Exposition
121 122 123 123 123 124 124 125 125 126 126 127 128 129 129 129 130 130 131 131 132 133 134 134 135 135 137 143 143 144 145 146 147 147 148 149 149 150 151 152 152 153
8.16 8.17 8.18 8.19 8.20 8.21 8.22 8.23 8.24 8.25 8.26 8.27 8.28 8.29 8.30 8.31 8.32 8.33 8.34 8.35 8.36 8.37 8.38 8.39 8.40 8.41 8.42 8.43 8.44 8.45 8.46 8.47 8.48 8.49 8.50 8.51
The main axis of the Shanghai Exposition with pools ﬁlled with treated river water Suspended solids in the water in the ﬁrst and the last stage of the wetland Plan view of the Houtan Park constructed wetland Broad range of submerged, ﬂoating leaf and emergent plant species that contribute to the treatment of the polluted river water The original condition of the Houtan park site Terracing, concrete boardwalk platforms and the division of the wetland bed into planting strips The boardwalk and terrace seating alongside wetland vegetation bands and upland terraces from the opposite direction Plan showcasing the arrangement of plant species in bands perpendicular to water ﬂow The 15 wetland compartments in treatment sequence Plan view of the initial stage of the wetland Initial stage of the wetland during construction Masonry wall with cut stone veneer, section The established wetland, Houtan park site Section through wetland, deck and steel sculpture created from waste material from the existing site Park terraces just before planting Section through planted terraces Wetland valley during construction Wetland valley completed landscape Early rendering of the proposal for Houtan Park illustrating the multifunctional character of the park Bamboo decking follows a vibrant ﬁberglass bench between two community agriculture ﬁelds Compressed spaces between verdant strands of reeds and grasses Panels punctuate the landscape and frame views of the city Shade structures supported by panels made from re-purposed steel create intimate spaces along the river Sequence of two- and three-dimensional elements fashioned from the steel plates Plan view of the steel elements Steel structure and paving along the boardwalk Steel paving and bench The bamboo boardwalk places the user at the water surface Fishing docks and terraces connected by steps that serve as seating This is the last pool before the treated water returns to the river Plan view of the last pool and the decks below the pergola The diverse planting at Houtan Park The terraced ﬁelds at Houtan Park Example of textures and colours The Sanlihe River Ecological Corridor The Tanghe River red ribbon bench and boardwalk
153 154 155 155 157 157 158 158 159 159 160 160 161 161 162 162 162 163 163 164 164 165 165 165 166 166 166 167 168 169 169 171 171 172 172 173
8.52 8.53 9.1 9.2 9.3
Aerial perspective of the Tanghe River project The Isar River restoration near Munich The Qunli National Urban Wetland Park The affects of human changes on increased stormwater run-off The bio-retention swale at Olympic College Parking Garden in Bremerton, Washington, USA 9.4 Stapleton community stormwater management 9.5 Map showing and deﬁning the four rainstorm types in the USA 9.6 Portion of an isopluvial map showing rainfall depth 9.7 Intensity–Duration–Frequency curve for a region in Delaware, USA 9.8 Map showing TR-55 analysis 9.9 The urban and suburban watersheds in the study of water quality in streams near Atlanta, Georgia 9.10 Decomposition of algae, as seen in this California urban stream 9.11 Suburban context of JEL Wade Park wetland 9.12 JEL Wade Park wetland 9.13 Plan view of the design for JEL Wade Park and wetland 9.14 JEL Wade wetland sedimentation basin and its outlet weirs 9.15a Plan view of stormwater management and treatment cells that operate in parallel 9.15b Perspective view of stormwater management and treatment cells 9.16 Perspective view of the subsurface ﬂow gravel wetland showing two treatment cells in series 9.17 Three-basin subsurface gravel wetland at the University of New Hampshire 9.18 Sedimentation basin of the subsurface gravel wetland at the University of New Hampshire 9.19 Schematic perspective of the piping system for the gravel wetland 9.20 Section through the gravel wetland 9.21 Subsurface gravel wetland at Greenland, New Hampshire 9.22 Bio-retention basin at Tabor School in Portland, Oregon 9.23 Bio-retention basin preceded by a vegetated swale to reduce sediment and heavy metals 9.24 Underground view of a bio-retention basin with a ﬂooded sub-basin (internal water storage) 9.25 Plants being treated formally in bio-retention basin, Portland, Oregon 9.26 Hal Marshall bio-retention basin with spring growth of vegetation 9.27 The Street Edge Alternative project in Seattle 9.28 Courtyard designed to receive stormwater in a park in Tianjin, China 9.29 Oregon City bio-retention basin 9.30 Aerial view of the context for the stormwater park Qunli, China 9.31 Aerial view of site Qunli, China 9.32 Land-use plan of the Qunli New Town 9.33 Plan view of the design for the stormwater park Qunli, China 9.34 Transfer process of a bio-retention basin
173 173 175 177 178 179 180 181 181 184 189 191 193 193 194 195 198 198 199 200 200 201 201 202 205 207 208 210 211 214 216 216 217 218 218 219 220
9.35 9.36 9.37 9.38 9.39 9.40 9.41 9.42 9.43 9.44 9.45 9.46 9.47 9.48 9.49 9.50 9.51 9.52 9.53 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15
Elevated walkways and pavilions shown in Qunli, China One of the two viewing towers in the Qunli wetland park Sedimentation basins at work as well as the mounds forested with birch trees Birch groves (Betula pendula) on hillocks Variety of species planted at Qunli wetland park Emergency spillways between the sedimentation and treatment basins Sediment and velocity control on-site Sedimentation basins connect to treatment pools and then to the core wetland Example of water from the nearby river supplementing the wetland during the dry season Siberian iris blooming in May Texture and colour of the wetland vegetation The Qunli wetland and park Restored hydrology supports low maintenance cost and provides seasonal diversity Example of spaces within the Wetland for small groups to sit Pavilion at Qunli wetland park Pavilion made of bamboo screen Winter scene of the pavilion made from cord wood The high production of biomass creates a highly diverse ecosystem Variety of user amenities as well as a dramatic seasonal display of perennial ﬂowers Constructed wetland at a ﬁeld edge that receives agricultural drainage water A ﬁeld-edge wetland along the Coldwater River Biologist Charles Bryant and Richard Lizotte measuring water quality in the linear wetland The Red River Research Station constructed wetland Phytoplankton bloom in the Bay of Biscay, France Distribution and size of dead zones along with ocean carbon content and human population density Transparent perspective of a denitrifying wetland Dairy cattle signiﬁcantly increase the phosphorus load in the Town Brook, New York watershed Stormwater drainage from a feedlot pen overﬂows into a basin where sediments can settle Iowa State University Beef Nutrition Farm Sheet ﬂow of stormwater across the feedlot pen is collected in a swale to allow solids to settle out Diagram of the treatment sequence for a Vermont dairy Manure composting facility Will Allen illustrates that tilapia production can be combined with plant production for a holistic approach Catﬁsh are inspected in a ﬁsh farm at the Warmwater Aquaculture Research Unit in Stoneville, Mississippi
220 221 222 222 222 223 224 224 225 225 225 226 227 227 227 228 228 228 229 234 235 236 238 239 240 241 242 243 243 245 245 248 249 249
10.16 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 11.11 11.12 A.C.1 A.C.2 A.C.3
Trout farm situated to allow water routed from streams to ﬂow through Aerial view of a hybrid wetland treating industrial pollution within the golf course in Casper, Wyoming This groundwater remediation project in Casper is embedded within a Robert Trent Jones golf course The horizontal subsurface ﬂow wetland is the last treatment step in the hydrocarbon removal project in Casper, Wyoming Mandan reﬁnery sequence of ponds and swales Wastewater treatment wetland in Oman Oman oil recovery and wastewater remediation Artiﬁcial wetland in Oman The treatment wetland during construction View toward the northeast of the wetland showing the ﬁrst stage of the treatment wetland Horizontal subsurface wetland featuring Cattail (Typha) Full-scale wetland treatment of efﬂuent from a coal-burning power plant in Kansas Section of the vertical subsurface up-ﬂow wetland Composite CN with connected impervious area Composite CN with unconnected impervious areas and total impervious area less than 30 per cent Soil texture classiﬁcation
252 255 256 256 257 258 258 259 262 262 263 265 266 274 275 276
Tables 2.1 2.2 3.1 3.2 3.3 3.4 3.5 4.1 4.2 4.3 5.1 6.1 6.2 8.1 8.2 8.3 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 10.1 10.2 11.1
Characteristics of raw sewage in the United States Typical septic tank efﬂuent concentrations Concentrations and removal of contaminants in a free water surface treatment wetland Water quality standards and performance of the E L Huie Treatment Wetlands Ofﬁcial visitors in the Talking Water Gardens Ammonia and nitrogen removal Bird species photographed at the Talking Waters Gardens Common substrates Residential horizontal subsurface ﬂow wetland, Zitenice, Czech Republic Treatment efﬁciency of Horizontal Flow Constructed Wetland at Spa´lene´ Por´´ıcˇe´, Czech Republic Mean inﬂuent and efﬂuent from the two-stage French system treatment wetland system Contaminant average concentration by treatment stage Mean values of emerging organic contaminants in the hybrid wetland stages Huangpu River water quality Project calendar Chinese water quality standards Recommended run-off coefﬁcients for the rational method Runoff curve numbers for urban areas Stormwater run-off pollution concentration and land use Levels of parking lot contaminants after a 28-day antecedent dry period Mean contaminant concentration for six roads in Texas Pollutant mean concentrations entering and exiting the wetland Horizontal subsurface ﬂow gravel wetland pollution removal performance Hal Marshall bio-retention basin pollution removal performance Net mass removal of pollutants from sequential urban run-off storms Reduced curve number and depth of rainwater to inﬁltrate Sediment, nutrient and pesticide concentrations in the wetland at 100 m from the inlet Feedlot wetland performance Summary of tannery efﬂuent treatment performance at the hydraulic loading rate of 6 cm per day and a hydraulic residency time of 7 days
26 30 39 40 44 45 46 60 64 65 82 91 93 151 154 156 183 185 186 187 188 196 204 212 213 215 237 244
11.2 A.A.1 A.B.1 A.B.2 A.C.1 A.C.2 A.C.3 A.C.4 A.C.5
Hybrid wetland and the removal of metals Plants by continent Plant species for Houtan Park, Shanghai China Aquatic species for Houtan Park, Shanghai China Run-off curve numbers for cultivated agricultural lands Run-off curve numbers for other agricultural lands Run-off curve numbers for arid and semiarid rangelands Run-off depth for selected CNs and rainfall amounts Criteria for assignment of hydrologic soil groups (water-impermeable layer less than 100 cm deep) A.C.6 Criteria for assignment of hydrologic soil groups (water-impermeable layer greater than 100 cm deep) A.C.7 Soil particle sizes A.C.8 Soil inﬁltration rates A.C.9 Plant species within the JEL Wade Wetland, Wilmington, North Carolina A.C.10 Bio-retention basin plants – Paciﬁc Northwest, USA
265 269 271 271 272 273 273 274 275 275 276 276 277 278
Acknowledgements I’d like to thank the many people that have made this book possible. I’m grateful to Kongjian Yu for generously providing images, drawings and documentation of his many amazing landscape architectural projects in China. They are truly courageous and inspirational. I want to thank him for his kindness during my stay in China. I’m also grateful for the support of Wei Li at Turenscape. My visits to the many projects by Kongjian Yu and his ﬁrm, Turenscape, were made possible by Zhenyu Liu. Zhenyu’s efforts in arranging my travel, his companionship and discussions of the projects on-site enriched my experience and this book. I am also grateful to Zhenyu for the three dimensional models used to illustrate the book. Stephen Drown and my wife, Leslie, always provide support and patiently endure the messy and timeconsuming writing process. The reviewers, editors and staff at Routledge improve and reﬁne my efforts with great skill. I thank them for their understanding and patience when my health took a turn for the worse and delayed completion of the manuscript. Many individuals in the Creative Commons have shared images that illustrate the text. Thank you for your generosity. Other images and technical information that have made the book better and more comprehensive came from Hans Brix, Jan Vymazal, Michael Blumberg, Cristina Avila and Joan Garcia. I have relied on their careful and important research, and I thank them for the images and information that they generously shared. Finally, I’d like to acknowledge the great research and dissemination programmes at the Biological and Agricultural Engineering program of North Carolina State University and the University of New Hampshire Stormwater Center (Tom Ballestero and Robert Roseen) and the Centre for New Water Technologies in Spain. Gary Austin, 2016
1 Water and sustainable urban design Introduction This book addresses the intersection of development (both rural and urban), and the supply and quality of water required to sustain it. Sustainable development must include water quantity and quality as indicators applied to both human and ecosystem health. Furthermore, these indicators must be considered across the full range of human land uses, including urban, agricultural and industrial. In the planning for new urban centres, green infrastructure exhibits its potential as a continuous network of urban and natural spaces connected by ecological corridors. These linear and nodal green spaces structure the residential and commercial uses of the city while contributing many ecosystem services, such as pollution mitigation and provision of recreational open space. When a green infrastructure network is combined with high-density development, then compact, high-quality human environments are created (Austin, 2014).
Municipal master planning Establishing sustainable water use is more readily attainable when water supply and treatment infrastructure are incorporated into master planning. Retroﬁtting existing cities to achieve more sustainable use and disposal of water is possible, but requires intensive, coordinated efforts by government agencies and citizens through years of consistent effort. The city of Philadelphia, United States, is an example of a city with an aging infrastructure engaged in this difﬁcult but economically advantageous process today. The $1.2-billion-dollar plan will require 25 years to complete, but will save the city $5.6 billion by eliminating the need for new conventional wastewater treatment plants, upgrades to existing plants and conventional stormwater infrastructure. This effort includes constructed wetlands and other measures to convert one-third of the city’s impervious surfaces to pervious conditions to reduce stormwater contributions to the city’s combined stormwater and sanitary sewer infrastructure (Figure 1.1). Ultimately, the amount of stormwater entering Philadelphia’s waterways will be reduced by 85 per cent (Philadelphia Water Department, 2015). An example of green infrastructure master planning is in the city of Wuhan in the Hubei province of central China. Wuhan has a rapidly expanding population of more than 10 million people. The city receives about 47 inches (1,200 mm) of rainfall per year, much of it during the hot summer months. In east Wuhan, an area of
2 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.1 The city of Philadelphia is engaged in a citywide campaign to divert stormwater run-off into infiltration areas rather than into the combined stormwater and sanitary sewer system. Photo: Philadelphia Water Department. www.flickr.com/ photos/philadelphiawater.
6.2 square miles (10 km2) has been designated for a new town named Wulijie. The gently rolling topography of the new town will be the home of 100,000 residents. The existing valleys and ponds will form the basis of a surface stormwater collection and treatment network. Retaining and treating the increase in run-off created by urban buildings and paving are important to preserve the high water quality of Liang Zhi Hu Lake, which is downstream to the east (Saunders and Yu, 2012). Figure 1.2 shows two sensitivity maps for the proposed development area. One studies the hydrology and the risk of ﬂooding, while the second considers the habitat value and cultural sites. A composite of these plans led the planners to the conﬁguration of the residential and commercial development blocks as well as the transportation network. Public transportation, pedestrian and bicycle systems were an integral part of the planning from the outset. The development plan is structured by three types of corridors. In Figure 1.3, the three corridor types are distinguished by width and clearly establish the form and scale of the new town districts. The orange line indicates the major vehicular transportation routes. The hierarchy of corridors speciﬁed in the master plan will accommodate increasingly greater stormwater run-off volumes. The tertiary corridors (Figure 1.4) are 50–100 feet wide (20–30 m); they receive stormwater from the development parcels and overﬂow to the larger corridors. The secondary corridors (Figures 1.5 and 1.9) are 200–300 feet wide (60–90 m); they subdivide the development blocks and deliver moderate stormwater ﬂows to the major water corridors. The widest corridors (Figures 1.6, 1.7 and 1.8) are 400–500 feet (120–150 m), which deﬁne the perimeter and major development sections. The width of the corridors (Figure 1.10) planned at Wulijie exceeds the minimum width recommended by ecological research and green infrastructure planning (Austin, 2014), which suggests minimum widths and lengths for ecological corridors. The
WATER AND SUSTAINABLE URBAN DESIGN 3
Figure 1.2 The plan on the left identifies flooding risk in three categories, while the image on the right shows outstanding habitat and cultural features. Image: Kongjian Yu, 2014.
Figure 1.3 This plan shows the flow direction for stormwater through the three corridor types. It is clear that this is a surface water management approach to stormwater. This approach allows ancillary benefits to be attached. These include urban habitat, recreation, open space and natural beauty. The resulting installation and maintenance costs are low compared to a catch basin and pipe system, but the advantages related to the environment and quality of life are remarkable. Image: Kongjian Yu, 2014.
4 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.4 The narrowest and the most urban corridors are surrounded by high-rise buildings. However, planted swales and basins collect and treat stormwater. A – bioswale; B – use node; C – pedestrian walk; D – infiltration basin; E – stormwater catchment; F – bioswale; G – pedestrian walk; H – bioswale. Image: Kongjian Yu, 2014.
Figure 1.5 This section through a secondary corridor (200–300 feet wide) illustrates the great attention to landform grading required to implement the surface drainage system and create treatment areas where non-point source pollution can be mitigated through filtration, sedimentation and biological processes. A – road; B – bioswale; C – bikeway; D – terrace; E – waterside path; F – infiltration wetland. Image: Kongjian Yu, 2014.
recommendations vary according to the context, but in a low-density residential district, the minimum recommended width is about 33–66 feet (10–20 m) and their length should be limited to 3,270–6,335 feet (1,000–2,000 m) before a habitat patch is provided. At the rural scale, the recommended maximum length of 1,300–6,335 feet (400–1,000 m) is paired with a minimum corridor width of 66–164 feet (20–50 m). In order to sustain urban biological diversity, the ecological corridors should connect to habitat patches having a minimum area of 1.2–12.4 acres (0.5–5 hectares). At the outskirts of the community or in rural settings, the habitat patches should have a maximum area of 124 acres (50 hectares) and spaced 6,335 feet apart (2,000 m) (Kubei, 1996). At Wulijie, the wide corridors are appropriate for high-density development. The patches of habitat are provided at the corridor intersections in the most highly developed areas or as nodes attached to the perimeter corridors. The corridors become narrow as development intensiﬁes, as shown in Figures 1.7 and 1.11. Both the public landscape and the development parcels have development controls to assure effective implementation. Figure 1.12 shows a small portion of the controlling plan for development. These controls include build-to lines and links to the development requirements including standards for the public landscape. This plan most clearly shows the tertiary corridors separating the development parcels.
WATER AND SUSTAINABLE URBAN DESIGN 5
Figure 1.6 The widest corridors (up to 500 feet wide) feature the best biological diversity, but recreation and stormwater storage and treatment are equally important. The intersections of the widest corridors create larger habitat patches. Image: Kongjian Yu, 2014.
Figure 1.7 This image shows an intersection between one of the widest corridors and an intermediate one. It is remarkably consistent with the character imagined in the drawing in Figure 1.6. Photo: Kongjian Yu, 2015.
Figure 1.8 This image of one of the widest corridors illustrates that they support significant habitat, as upland species of shrubs and trees are adjacent to extensive wetlands. The presence of such expansive open space within high-density urban development is rare. Photo: Kongjian Yu, 2015.
6 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.9 This is an intermediate corridor at Wulijie. The diversity and beauty of the planting design is inspiring, but this is also a working landscape. In the foreground, a basin captures sediment in the first step of water quality improvement. Photo: Kongjian Yu, 2015.
Figure 1.10 This image illustrates that there is great variety in the visual character coupled with diverse treatment strategies within the intermediate wetland corridors. Photo: Kongjian Yu, 2015.
Figure 1.11 The narrowest corridor is the most urban in character but sufficiently wide to provide space between the buildings for light and privacy. The width still accommodates the landscape infrastructure. Photo: Kongjian Yu, 2015.
WATER AND SUSTAINABLE URBAN DESIGN 7
Figure 1.12 The controlling plan for a small section of the new town of Wulijie. Image: Kongjian Yu, 2014.
8 WATER AND SUSTAINABLE URBAN DESIGN
Material selection, architecture featuring passive and active solar technology, public transportation options and other factors must be added to the consideration of stormwater, open space, recreation and habitat in order to build a city with minimum adverse environmental impact. Indeed, a high-speed train station and other features are included in the plans for Wulijie. The ﬁrst phase of the new town is complete. As other sections are completed and the project matures, we will have a new model of sustainable development to monitor and learn from. The images of the planning documents, conceptual perspectives and, most importantly, the installed landscape shown here indicate that the result fulﬁls the promise of the artist’s rendering in Figures 1.13 and 1.14.
Figure 1.13 The artist’s rendering of the proposed development shows the major ecological corridor in the centre and to the right in this night-time scene. The secondary corridors establish smaller districts, while the narrowest corridors separate the buildings. Image: Kongjian Yu, 2014.
Figure 1.14 This image shows where the primary and intermediate corridors meet. Consistent with the planning and design intensions, the narrower corridors capture and treat stormwater run-off. During large storms, the narrow corridors conduct floodwater to wider corridors in the network. Boardwalk and other pathways invite the urban dweller to explore the naturalistic network. Photo: Kongjian Yu, 2015.
WATER AND SUSTAINABLE URBAN DESIGN 9
Water resource planning The allocation of water resources often occurs at the scale of the state or province rather than at the municipal scale, such as in Wulijie. The quantity of water allocated to users in the United States is regulated by state governments rather than by a national policy or regulation. However, the federal government participates by way of the development of water resources and distribution through dam construction and irrigation supply programmes, for example. Federal mandates, such as the Endangered Species Act, also establish a minimum allocation for aquatic ecosystem health. With the major exception of irrigation, most water allocations are non-consumptive. Water is used and returned to surface water, although at a lower quality, generally. In this way, freshwater is reused. Constructed wetlands play a limited role in increasing the quantity or supply of potable water, but they can have a signiﬁcant impact on the quality of water available for reuse, especially reuse for non-potable purposes. The quality of water returned to streams, rivers and lakes is critical to the healthy function of the ecosystem and the ecosystem beneﬁts that accrue to humans. Constructed wetlands can play an important role in achieving water quality that fosters ecosystem and human health.
Water quantity There are recent positive trends in water consumption, which show a 13 per cent decrease in water use between 2005 and 2010 in the United States. Self-supplied industrial withdrawals of water were 15.9 billion gallons per day in 2010, which is a dramatic decline from the peak use of 47 billion gallons per day in 1970 (Maupin et al., 2014). The national government assesses water use every 5 years and the next dissemination of data is scheduled for 2016. It is useful to know how the water use was distributed in order to devise a plan to efﬁciently allocate, recycle, treat and reuse existing water resources. In the United States, legally binding water rights allocate almost all of the surface water. Agriculture and industry use the great majority of surface water, while municipalities depend much more on groundwater for potable supplies or water that can be treated to potable standards. An estimated 355 billion gallons per day was used in the United States in 2010, although 48.3 billion gallons per day of saline water was used primarily as industrial cooling water. Of the 306 billion gallons per day of freshwater used, 230 billion gallons were from surface water while 76 billion gallons were withdrawn from groundwater (Maupin et al., 2014).
Thermoelectric power and agricultural industries While thermoelectric power generators and agricultural irrigators are the two greatest users of water, both showed a decrease in consumption compared to 2005. Thermoelectric power generation industry used 161 billion gallons per day and irrigation used 115 billion gallons per day (a 20 per cent and 9 per cent drop, respectively, compared to 2005). Nevertheless, thermoelectric power and irrigation each used 38 per cent of the water, totalling to 76 per cent of all freshwater withdrawals. Most of the irrigation water (65.9 billion gallons per day, 57 per cent) was derived from surface water while the remainder (49.5 billion gallons per day) came from groundwater
10 WATER AND SUSTAINABLE URBAN DESIGN Figure 1.15 Spray irrigation is intermediate in efficiency between flood and drip irrigation. Shifting from flood to spray or from spray to drip irrigation has the potential to free significant volumes of water for other uses. Photo: Gary Austin, 2015.
(Maupin et al., 2014). The enormous volumes of water used by these sectors and the high percentage of total water use suggest that explorations of increased water use efﬁciencies, recycling and treatment measures in these sectors could yield signiﬁcant water resources that could be used elsewhere. For example, ﬂow-through cooling systems remain the most predominant cooling method for coal-ﬁred power plants, withdrawing about 55 billion gallons of water per day (Diehl and Harris, 2014). The conservation potential is clear from an understanding that water use produced from each kilowatt-hour of energy ranges from 75 gallons per kilowatt-hour to 0.4 gallons per kilowatt-hour based on ﬂow-through, recirculation or dry-cooling systems. In 2010, about 62,400,000 acres of land was irrigated, of which 58 per cent was spray irrigation. The most wasteful irrigation method, ﬂood irrigation, accounted for 26,200,000 acres (42 per cent). Again signiﬁcant water resources can be conserved through a shift in irrigation technology. A positive irrigation trend is the decrease in the depth of agricultural irrigation, from more than 4 feet to about 2.1 feet in 2010. In contrast, the domestic use of water accounts for only 1 per cent of all water withdrawals. Therefore, efforts to reduce use or recycle and reuse water are important where groundwater supplies are limited and in arid areas where water supply is imported from another region (Maupin et al., 2014). Water use in other economic sectors also declined with the exception of mining (5.32 billion gallons per day) and aquaculture (9.42 billion gallons per day). Most of aquaculture’s surface water withdrawals occurred at facilities that operated ﬂowthrough raceways. Water used for livestock was 2 billion gallons per day, of which 60 per cent was from groundwater (Maupin et al., 2014).
Urban stormwater run-off quantity A considerable amount of rainwater that would normally inﬁltrate into the soil to recharge aquifers or supply streams and lakes during the dry season now ﬂows off
WATER AND SUSTAINABLE URBAN DESIGN 11
pavement and roofs. The greater volume of run-off also ﬂows away at a greater velocity. These changes in inﬁltration and run-off generate great volumes of polluted run-off by cities (Figure 1.16). For example, Denver, Colorado, covers 153 square miles and generates over 2.6 million gallons of water from a 1-inch rainstorm. Most of this amount runs off into streams and rivers through the storm sewer piping system (Sipes, 2010). A certain amount of this stormwater is detained in stormwater basins, but these are rapidly drained. Very few of the basins are designed to retain signiﬁcant amounts of stormwater run-off. Even fewer are designed to inﬁltrate captured run-off to recharge groundwater supplies or to maintain base ﬂow (underground discharge) of water to sustain local streams through the dry season. These circumstances exist today despite current construction wetland technology to establish landscapes that retain stormwater run-off and cause it to inﬁltrate.
Climate change National governments need to urgently mitigate the already occurring impacts of climate change. Even more urgently, we must put adaptation plans into effect to respond to the worsening conditions that we can no longer avoid during the next few decades. Increased stormwater ﬂows and periods of drought will occur but in an irregular pattern across the globe (Figure 1.17). We will experience more rainfall during the most intense storms. This trend is already evident, as the amount of rainfall during the largest storms (1 per cent) has increased by nearly 20 per cent during the last 50 years. More precipitation is already falling as rain rather than as snow, causing increased stream ﬂow in the wet months and decreased ﬂow during the dry months for rivers that have headwaters in the mountains (US Environmental Protection Agency, 2015). The use of constructed wetlands designed to include inﬁltration is one
Figure 1.16 The size of stormwater outfall pipes suggests the tremendous volumes of, often untreated, water that discharge to waterways. Photo: Darkday. License: CC-BYSA-3.0.
12 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.17 The impact of climate change on precipitation will have different impacts in regions of the United States and even within individual states. This map shows the trends from 1958 to 2007. The hatched areas identify significant trends. Image: US Global Change Research Program. License: government work product. www3.epa.gov/climatechange/images/impacts-adaptation/USdrought-large.jpg.
way of adapting to climate change, as this will increase base ﬂow to rivers and streams during the dry season. The changes in surface water have other economic and ecosystem impacts that must be mitigated. Increased volumes of stormwater run-off in urban areas have signiﬁcant implications for the existing urban stormwater management infrastructure. For example, many cities are making adjustments to their stormwater detention and retention standards to prevent future ﬂooding caused by climate change. Climate change impact studies for Europe indicate regional alterations in river ﬂow, with the greatest impacts in the Mediterranean zone (due to reduced precipitation) and in the northern forest areas due to reduced snowpack, faster snowmelt and subsequent ﬂood risk. In the Mediterranean areas, reduced river ﬂows are anticipated in all months by 2050. The reduced river ﬂow will expose species to increased extinction pressure. In addition, lower ﬂows may increase water allocation conﬂicts, since existing water withdrawal for irrigation and other human uses may be reduced to assure species preservation. For example, there will be an increased need to direct ﬂows to ﬂoodplains to sustain existing ecosystems (Schneider et al., 2013).
Groundwater Some categories of water are particularly precious, such as the pure sources of drinking water. Groundwater sources of drinking water should be protected from
WATER AND SUSTAINABLE URBAN DESIGN 13
contamination by disease-causing organisms or toxic substances. Again, constructed wetlands can be used as a sustainable development measure to capture polluted water and reduce the concentration of contaminants before the water inﬁltrates into groundwater reservoirs. Figure 1.18 shows a map of the principal aquifers in the United States. Where these are the sole source of potable water, the quantity and quality of the water contained in the aquifer are critical to the survival of the cities, towns and people that depend on them. Generally, municipalities must share groundwater with agriculture and industrial users. Aquifers are composed of sands, gravel and porous stone layers that are often hundreds of feet below the surface but in other instances are near the surface due to underlying geology. Water is added to aquifers by inﬁltration of rain and surface water through permeable soils. The rate at which aquifers are recharged is limited by the amount of rainfall, soil inﬁltration rate, and the presence of ponds and lakes. In order to restore the quantity of water withdrawn from aquifers by humans, the recharge areas must be identiﬁed and preserved. Covering them with impermeable paving and buildings compromises the amount of water that can enter. As they are below ground, it is rather difﬁcult to quantify the volume of water contained within an aquifer. However, it is a simple matter to measure the distance from the surface to the top of the aquifer using groundwater wells. When the distance consistently increases, this means that the carrying capacity of the aquifer is being exceeded. More water is being withdrawn than is being replenished. As the volume of the aquifer is often unknown, it is difﬁcult to predict the amount of time this
Figure 1.18 Principal aquifers in the United States. The United States Geological Survey (USGS) provides current and historical information about groundwater at http://waterdata.usgs.gov/nwis/gw. Image: US Geological Survey, 2003. License: government work product, http://waterdata.usgs.gov/nwis/gw.
14 WATER AND SUSTAINABLE URBAN DESIGN
unsustainable situation can continue before the aquifer is depleted. It is, however, certain to occur eventually if there are no changes in the consumption or recharge rate. Increasing the inﬁltration of water in the recharge areas or substituting surface or reclaimed water for non-potable uses to conserve the pure groundwater are two options that might correct the sustainability balance. In either case, constructed wetlands have a signiﬁcant role to play. Aquifers near the surface are more readily subject to pollution from human activities. When this occurs, it is possible to pump contaminated groundwater and treat it in constructed wetlands to remove the pollutants. The chapter on industrial applications presents a wetland that treats groundwater contaminated with hydrocarbons. The quality of groundwater wells decreased between 2000 and 2010 compared to the period of 1988–2000. Although the quality was unchanged in about half of the wells, many wells showed increased levels of chloride, dissolved solids and nitrate. Nitrate was higher in 23 per cent of the wells tested (US Geological Survey, 2014).
Water quality Water resource planning generally focuses on supply and allocation, and less often on treatment for reuse and recycling as a strategy of expanding water quantity. A primary beneﬁt of constructed wetlands associated with development is the treatment of various types of wastewater, so that they can be reused or discharged to the environment without causing adverse ecosystem impacts. In the case of reuse, treated water could be applied to consumptive uses, such as irrigation, or non-consumptive uses, such as toilet ﬂushing or industrial cooling and process water. In both cases, the reuse of water treated by constructed wetlands reduces the demand for high-quality water diverted from surface water or groundwater. A second important beneﬁt of constructed wetlands is the protection or restoration opportunity to return water to streams, rivers, lakes and coastal areas that is pure enough to foster ecosystem health. Treating agricultural, industrial and urban efﬂuents and stormwater to this quality is a major challenge that the United States and other countries are only beginning to address. This book contains chapters on the application of constructed wetlands for treating human wastewater, stormwater, agricultural and industrial wastewater. Whether or not we like to think of it, water from rivers and groundwater is recycled after treatment for subsequent use by humans and a host of other organisms. Cities along the lower Mississippi and Yangtze Rivers, for example, withdraw, treat and consume water that has been previously used, treated and discharged upriver. In this scenario, it is clear that all water entering the river should be treated to as high a quality as is technically and economically feasible in the interest of other human and non-human users. Surprisingly, in the case of urban stormwater, ﬁlthy water is allowed to ﬂow into streams and rivers untreated. Constructed wetlands are effective and reliable options for the treatment of human wastewater as discussed extensively in the initial chapters of this book. About 25 per cent of Americans use septic systems rather than a connection to sanitary sewer networks that deliver wastewater to centralized wastewater treatment plants. The estimated lifespan of septic systems ranges from 20 to 27 years. Between 5 per cent and 35 per cent of these septic systems do not function correctly due to age, poor design and maintenance, or due to construction in unsuitable soils. Failing
WATER AND SUSTAINABLE URBAN DESIGN 15
septic systems are the source of signiﬁcant non-point source pollution of groundwater, streams and lakes (Sipes, 2010). Small-scale applications of constructed wetlands to replace individual septic systems or those serving groups of homes would greatly reduce non-point source pollution.
Barriers to sustainable water use The manner and cost of water allocation among users, the unwillingness to pay for treatment of contaminated water, centralized wastewater treatment and the lack of redistribution piping for reclaimed water are conditions that lead to wasteful use of water. As pure water is an essential resource, assuring a sufﬁcient and consistent supply and quality is a basic and primary responsibility of any municipality. Yet we commonly ﬁnd that citizens, business groups and even municipal governments thwart efforts to protect water supplies, especially to treat contaminated water to desirable levels before discharging it downstream. This avoidance of responsibility for cleaning one’s mess transfers the problem and cost of full treatment for reuse or discharge to healthy ecosystems to other agencies or municipalities who are also downstream. Adopting this subterfuge is unnecessary since low cost technologies can be applied and multiple beneﬁts can be derived from local treatment and reuse. The economic and multiple functions of treatment wetlands is a consistent theme in the chapters that follow. A certain amount of water is a free ecosystem service to municipalities and even property owners. However, the cost of purifying, storing, distributing or pumping from aquifers and rivers can be high. This cost is often not transferred to the water user, but is instead subsidized by the municipality or water district and funded by tax revenue from other sources. This leads to a mistaken assumption by the consumer that water is inexpensive and abundant when, in fact, it is neither. This situation results in excessive and wasteful use of water, as this behaviour has no economic or supply consequence in the short term.
Domestic water use and cost A very high per capita use of domestic water in places such as Las Vegas, which are almost entirely dependent on importing water from beyond the region, is the perplexing result of water pricing and policy. High per capita use is partly the result of the climate. For example, in arid Las Vegas, the per capita use is about 110 gallons per day, while in the Boston, where there is ample rain, the per capita use is about 40 gallons per day. However, price is also a factor. In Las Vegas, the monthly cost for a family of four using 100 gallons per person per day is about $42, while in Boston, the cost for the same amount is about $78 (Walton, 2010). In the European Union, nine states have a per capita domestic water use of 30 gallons per day or less. However, arid Greece has a per capita use of about twice this amount. The per capita use in the United Kingdom is about 44 gallons (European Union, 2014). The cost of water in Europe ranges from $0.46 up to $6.58 (€0.40–€5.75) for 264 gallons (1,000 litres) with an average price for 65 nations in Western Europe of $2.19 (€1.91) for 264 gallons (1,000 litres) per month. The price is based on the use of 15,000 litres per person per month (132 gallons, 500 litres per person per day). Higher rates are charged for additional quantities (Conroy, 2013). In comparison to
16 WATER AND SUSTAINABLE URBAN DESIGN
US prices, the monthly cost of water for four people using 100 gallons per day would range from $22.50 to $322 (with an average of $107.24). In the United States, the cost of water also varies widely based on its source, quality and economic sector. Agricultural customers are often able to purchase an acre-foot of water for $10, which is less than the cost to provide it. In contrast, urban residential customers might pay $230 for the same amount (Sipes, 2010).
Centralized wastewater treatment Centralized versus decentralized application of water treatment efforts is a question that arises when planning for reuse. Metropolitan areas of industrialized countries adopted a centralized and industrial approach to the treatment of municipal sewage long ago. Most municipal wastewater treatment plants depend on gravity ﬂow wherever possible to deliver raw sewage to the treatment plant. This is to avoid the cost of pumping water. In practice, this means that the treatment plant is located at the lowest elevation in the community. Therefore, reuse of the treated efﬂuent would require pumping the treated water uphill to the prospective customers within the same community. This system of trading energy for reclaimed water is not an optimal sustainability strategy. A decentralized approach to wastewater treatment in a city makes the distribution of treated efﬂuent for non-potable uses, such as irrigation, more feasible as gravity ﬂow can be utilized. Opportunities for decentralized wastewater treatment, whether through conventional or constructed wetland systems, are possible as cities expand through new development. Decentralized treatment encourages residential water reuse for non-potable applications, such as toilet ﬂushing, or recycling in the case of industrial and aquaculture applications.
Distribution piping for reclaimed water Associated with the disadvantages of centralized wastewater treatment at the lowest elevation in a municipality is the absence of a non-potable water piping network to redistribute the treated efﬂuent. It is not economically feasible to retroﬁt existing developed areas with this piping, except in the most dire circumstances, but it is feasible for new development. As reclaimed water can be used for any non-potable use within or outside buildings, the demand on potable water from groundwater or treated surface water can be signiﬁcantly reduced.
Condition of wetlands and streams Since the days of the Cuyahoga River (Figure 1.19) in Cleveland and rivers in other cities repeatedly catching ﬁre between 1900 and 1969, we have made good progress in the United States and in other nations in controlling point sources of water pollution. However, natural systems can be overwhelmed and damaged by high concentrations of excess nutrients and toxic substances that originate from both point and non-point sources. The resulting loss of ecosystem health in turn compromises the potential of human health and economic systems. An assessment of the conditions of waterways and water bodies reveals an unsustainable course that can be corrected with little cost but sustained attention. Wetland ecosystems have greatly diminished in size in every country. Although the
WATER AND SUSTAINABLE URBAN DESIGN 17 Figure 1.19 Images such as this one of the Cuyahoga River on fire in 1952, but published in 1969, shocked the nation. Photo: James Thomas, Courtesy of Cleveland Press Collection at Cleveland State University Library. License: public domain.
United States now operates under a ‘no net loss’ policy, more than 50 per cent of the original wetlands in the country have been destroyed. The situation is even worse in New Zealand where only 8 per cent of the original wetlands remain. These losses are ecologically devastating, as wetlands made up only a small portion of the total natural landscape but are critical to both aquatic and terrestrial species (Sipes, 2010). New constructed wetlands can replace some of the historic wetlands that were drained to produce agricultural plots or urban development sites. A comprehensive study of rivers and streams in the United States revealed that more than 55 per cent of the length of the nation’s rivers and streams are in poor condition (Figure 1.21). The assessment is based on biological indicators, such as aquatic insects, as this is also an indirect measure of the physical and chemical conditions. The study revealed regional differences with rivers and streams in the eastern United States having the most impaired water. The poor or fair biological conditions result, in part, from high levels of nitrogen and phosphorus. High nitrogen levels and high phosphorous levels were found respectively in 40 per cent and 28 per cent of the river and stream lengths (US Environmental Protection Agency, 2013). Wastewater contributes large quantities of both phosphorus and nitrogen to natural streams through discharge from sewage treatment plants, although agricultural run-off from crop-land and feedlots, and industries that process food such as milk, cheese, wine, beer, potatoes and meat, can also contribute great amounts of these excess nutrients. Constructed wetlands and land applications of treated efﬂuent can reduce phosphorus and other contaminants in a very economical manner (Figure 1.20). The example of Roseburg, Oregon, illustrates that the three aspects of sustainability (economic, social and environmental) can be achieved simultaneously. It seems obvious that agricultural and domestic applications of herbicides and insecticides that run-off with stormwater would have a negative impact on natural aquatic ecosystems. Levels of these chemicals that can kill or disrupt growth and reproduction of aquatic organisms after several hours of exposure are characterized as chronic level impacts. During 2002–11, chronic levels of pesticides impacting aquatic organisms were measured in about two-thirds of streams in agricultural areas and
18 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.20 The city of Roseburg, Oregon, spent $10 million to purchase 350 acres of land, restore a degraded wetland and construct a holding pond, pumping station and irrigation system to spray treated effluent from their conventional wastewater treatment plant to reduce the amount of phosphorous reaching the receiving river. This alternative saved $90 million compared to an upgrade to the wastewater treatment plant that would have achieved the same result. The open space and wildlife benefits resulting from the land application of the wastewater were free. Photo: Gary Austin, 2013.
Figure 1.21 The conditions of rivers and streams in the United States based on the presence and health of biological indicators (macroinvertibrates) (US Environmental Protection Agency, 2013). Image: US Environmental Protection Agency. License: government work product.
WATER AND SUSTAINABLE URBAN DESIGN 19
about half of the streams in areas with a mix of land uses. Streams in urban areas contained chronic levels of pesticides in 90 per cent of the streams (Stone, Gilliom, and Martin, 2014). Constructed wetlands can reduce the concentration of nitrogen and phosphorus and, surprisingly, pesticides as well. Physical changes to the rivers and streams also compromise the biological conditions. The loss of riparian vegetation and the degree of human activities near the rivers and streams were found to be most detrimental to biological conditions. The sedimentation of the rivers and streams indicated a 60 per cent likelihood of poor biological conditions (US Environmental Protection Agency, 2013). Linear constructed wetlands for the treatment of polluted river water is the topic of one of the chapters in this book. Another chapter on constructed stormwater wetlands addresses the problem of sedimentation of natural waterways. Human health can also be compromised by the poor conditions of rivers and streams, and the United States’ national assessment found that more than 13,000 miles of river length was associated with mercury levels in ﬁsh tissue that exceeded safe human health standards. For streams, 9 per cent of their length was associated with pathogenic bacteria (enterococci) at levels exceeding health standards (US Environmental Protection Agency, 2013). Heavy metals associated with urban stormwater run-off and industrial efﬂuents are effectively removed by constructed wetlands. Similarly, high levels of pathogens are dramatically reduced in constructed wetlands treating domestic and livestock sewage.
Constructed wetlands and sustainable development Sustainability is an oft-bandied term that has lost some of its meaning through common use and misapplication. ‘Sustainability’ in this book is an assertion that there is a link between the health of human systems and ecosystems. The authors recognize that there is capacity in natural systems to adapt to greater or lesser inputs of nutrients and contaminants from both anthropogenic and natural sources. We acknowledge that there are technological and, more often, economic limits to the removal of pollutants generated by urban development, agriculture and industry. Sustainable development proposals are not quests for perfection. Instead, they illustrate the acquisition of technology, practices and outcomes that lead to continuous economic growth and ecosystem health rather than levels of contamination that will result in the collapse of human or natural systems and transfer the cost and suffering this collapse causes to future generations. It is necessary to develop a philosophical and conceptual basis for integrated water management and human development. This includes the agricultural and industrial enterprises that support human settlements but are located in the hinterland. Many cities in the United States, Europe and Asia have exceeded the carrying capacity of their aquifers for potable water. Water returned by agriculture and industry to groundwater or to natural receiving waters is invariably contaminated to some degree even when it is in compliance with wastewater discharge regulations. Wineries, breweries, dairy and other food processing industries generate high levels of organic pollutants. Heavy metals, phenols and hydrocarbons and solvents are by-products of mining (Figure 1.22), manufacturing and petrochemical factories, and energy production. In many nations, these point-source pollutants are inadequately removed from the efﬂuent discharged to the natural environment.
20 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.22 Pollution of a small stream from mine tailings. Photo: Admerial Crunch. License: CC-BY-SA-2.0.
Furthermore, the rainwater that replenishes the surface water collects pollutants as it ﬂows across urban, agricultural and industrial surfaces before it reaches natural streams and rivers. This contaminated run-off is non-point source pollution that is joined by municipal sewage efﬂuent, which contains concentrations of nitrogen, phosphorus (Figure 1.23), pharmaceuticals and chlorine or other substances even when it has been treated to the common secondary efﬂuent standards. Wastewater and contaminated stormwater run-off degrade the quality of water in receiving streams and rivers, especially those that are efﬂuent-dominated. The characterization of water in its relationship to human settlement described above is far from a model for sustainable management of water supply and water quality. Of course, the consequences accrue most tragically to aquatic organisms that must survive in the waste created by humans. Impact of an aquatic ecosystem can occur near the pollution source or hundreds of miles away. Rapidly enlarging dead zones along the coasts in the temperate zones of the world and especially at the outfall of polluted rivers, such as the Mississippi and the Yangtze, are dramatic illustrations of the cumulative impacts of municipal, agricultural and industrial discharges along hundreds of miles of the watershed. Failing ecosystem health in streams, rivers, lakes and oceans is indicator and indictment of the unsustainable use of water.
Figure 1.23 Excess nutrients from agricultural and domestic wastewater cause algae blooms that can result in oxygen levels that are too depleted to sustain fish and other aquatic organisms. Photo: Eric Vance, US EPA. License: government work product.
WATER AND SUSTAINABLE URBAN DESIGN 21
The recommendation to clean our mess as and where we make them is a lesson learned in kindergarten, which is beﬁtting as a sustainable water quality principle. However, an unwillingness to adopt sustainable water management by citizens, municipalities and companies is too simple an explanation for the predicament we ﬁnd ourselves in. Citizens have little direct control of the pollution created by their automobiles or the electrical energy power plants that supply their needs. Stockholders demand proﬁts but rarely sustainable practices. Our progress towards a sustainable society is thwarted as our attention is diverted by extremities in weather, ﬂoods and droughts, even though these climate change impacts are caused, in part, by unsustainable human practices. In the case of climate change, wilful ignorance is a perplexing obstacle that curtails creative thinking, research and implementation of solutions. Of course, constructed wetlands cannot mitigate climate change impacts but they can help us adapt to our changing circumstances. Some sustainability questions are how well should we clean the mess we create and how much should we attempt to recover and reuse? How clean should treated efﬂuent be? Do we have the technology and can we afford the cost to clean wastewater as well as we would like? Can we solve the logistical problems and bear the cost of delivering reclaimed water for reuse? This book offers answers to each of these questions. How clean depends on which use the reclaimed water is put to. If discharged into the environment, the answer is simple – clean enough to sustain natural ecosystems. Unfortunately, deﬁning this standard for the array of contaminants is more difﬁcult, but possible, as this book will illustrate. If the efﬂuent is to be reused in the industrial process, the quality can often be much lower than for potable water. If the reuse is for irrigation, high nitrate levels are actually desirable, but high salt levels are not, for example. The reader will be required to assess the technology and the performance of the various constructed wetlands with regard to the context and intended reuse goals. However, in every case, we should strive to decrease the vulnerability of our communities and increase their resilience. An interdisciplinary approach and a search of multiple functions will guide us towards these goals.
Types of constructed wetlands There are three basic types of constructed wetlands; this book comprises a chapter on each, which discusses their characteristics, uses, construction and performance. In these initial chapters, the designs and performance data focus on the treatment of domestic sewage, for which each type was originally developed. Subsequent chapters discuss the application of the three types of wetlands, and their combinations, for the treatment of stormwater and agricultural and industrial wastewater. Another chapter discusses constructed wetlands for the treatment of polluted river or lake water. The ﬁrst type of constructed wetland is called a free water surface wetland (Figure 1.24). This type is similar to a shallow marsh and features a depth of water on the surface. The free water surface wetland supports emergent vegetation such as common reed or cattail, and ﬂoating vegetation such as duckweed or submerged plants. Often all types of vegetation are present. Chapter Three explores free water surface wetlands. The second basic type of constructed wetland is called subsurface ﬂow wetland (Figure 1.25). In these wetlands, water is below the surface in a bed of ﬁlter media such as sand or gravel. There are two alternate ﬂow options for the subsurface ﬂow wetland. In the horizontal subsurface ﬂow wetland, water moves laterally through
22 WATER AND SUSTAINABLE URBAN DESIGN
Figure 1.24 Free water surface wetland treating stormwater in Wulijie, China. Photo: Kongjian Yu, 2015.
the ﬁlter bed, while in the vertical subsurface ﬂow wetland, the water ﬂows vertically through the ﬁlter bed. For the vertical subsurface ﬂow wetland, water is typically applied to the top of the basin and ﬂows downward, but sometimes the water is added to the bottom of the ﬁlter bed and water is forced upward. Both subsurface types support emergent vegetation. Hybrid wetlands are a sequence of two or more of the basic constructed wetland types. They are designed to achieve the highest water quality or are applied to wastewater that is particularly difﬁcult to remediate. The common sequences are: • • • •
vertical subsurface ﬂow > horizontal subsurface ﬂow horizontal subsurface ﬂow > vertical subsurface ﬂow horizontal subsurface ﬂow > free water surface free water surface > horizontal subsurface ﬂow
Hybrid wetlands are also designed with multiple stages, where each stage is an independent cell within the sequence. Common sequences are: • • •
vertical subsurface ﬂow > vertical subsurface ﬂow > horizontal subsurface ﬂow vertical subsurface ﬂow > horizontal subsurface ﬂow > free water surface vertical subsurface ﬂow > horizontal subsurface ﬂow > vertical subsurface ﬂow
Finally, there are a number of enhancements that can be applied to the constructed wetlands, such as artiﬁcial aeration, bafﬂes or other elements to modify ﬂow.
Units Pollutants in water are measured in two ways. The concentration of contaminants is generally expressed as milligrams present within one litre (about a quart; mg/L). There are 1,000 milligrams per gram and about 28 grams per ounce. For example, the
WATER AND SUSTAINABLE URBAN DESIGN 23
Figure 1.25 Horizontal subsurface flow wetland in Casper, Wyoming, treating groundwater polluted with hydrocarbons. Photo: Gary Austin, 2015.
Figure 1.26 E. coli bacteria colonies in a culture dish. A maximum of 126 colonies per 100mL of water is the standard for primary recreational contact (swimming) set by the US EPA. Photo: Madprime. License CC-BY-SA-3.0.
US Environmental Protection Agency (EPA) standard for total suspended solids in secondary sewage efﬂuent is less than 30 mg/L (this is equivalent to 30 parts per million). Extremely low concentrations of contaminants are expressed in micrograms per litre (g/L). There are 1,000 micrograms in one milligram. Heavy metal concentrations in water are deﬁned this way. For example, stormwater from landscaping contains about 263 g/L of zinc. The second way of expressing pollutants is as weight (often called the pollutant load). This is simply calculated as the mg/L times the total volume of water in litres. In this way, we can deﬁne the total weight of phosphorous entering a river, for example. The US EPA has a programme that limits the pollutant load permitted for compromised or sensitive water bodies. The Total Maximum Daily Load (TMDL) is an example of a pollutant standard based on the total weight of the contaminant. For example, a wastewater treatment plant might be allowed to discharge no more than 90 kilograms (198 pounds) of phosphorous per year into a receiving river. Bacteria in water are reported as the number of colonies that form in culture dishes containing a water sample. The sample is generally 100 millilitres (about 3.3 ounces) of water. For example, Escherichia coli (E. coli) is a disease-causing bacteria and the US EPA has established a maximum of 126 colonies per 100 mL for water as the standard for primary recreational use. New testing methods (Quanti Tray Sampler) do not actually grow a culture of bacteria (Figure 1.26) and express the test results as the most probable number (MPN) of bacteria. The toxicity of pollution is sometimes distinguished as acute and chronic. Both are harmful, but the ﬁrst is short-term (hours) exposure while the latter is long-term (several hours or days). These terms are applied to aquatic ecosystems. For example, federal and state agencies test the effect of toxic substances, such as pesticides and heavy metals, on aquatic organisms to determine if death or impairment to growth or reproduction occurs at various concentrations of the contaminant when the
24 WATER AND SUSTAINABLE URBAN DESIGN
exposure is short-term and when it is long-term. The acute level of exposure is sometimes deﬁned as the maximum concentration, and the chronic level of exposure as the continuous concentration. The acute exposure to lead is 30 g/L for 1 hour for aquatic organisms according to the standard adopted by the state of Georgia, for example.
References Austin, G. Green infrastructure for landscape planning: Integrating human and natural systems. Abingdon, Oxon: Routledge, 2014. Conroy, N. “Domestic water charges in Europe,” Public Policy, 1 May 2013. [Online]. Available: www.publicpolicy.ie/domestic-water-charges-in-europe/. [Accessed: 5 October 2015]. Diehl, T. H. and. Harris, M. A. Withdrawal and consumption of water by thermoelectric power plants in the United States, 2010. Reston, Virginia: US Geological Survey, 2014. European Union, “Water statistics,” European Union, 2014. Kadlec, R. H. Treatment wetlands. Boca Raton, FL: CRC Press, 2009. Maupin, M. A., Kenny, J. F., Hutson, S. S., Lovelace, J. K., Barber, N. L. and Linsey, K. S. “Estimated use of water in the United States in 2010,” US Geological Survey, Circular 1405, 2014. Philadelphia Water Department, “Green city, clean waters,” Philadelphia Water, 2015. [Online]. Available: http://phillywatersheds.org/what_were_doing/documents_and_data/cso_long_term_ control_plan. [Accessed: 15 October 2015]. Saunders, W. S. and Yu, K. eds., Designed ecologies: The landscape architecture of Kongjian Yu. Basel: Birkhäuser, 2012. Schneider, C., Laizé, C. L. R., Acreman, M. C. and Flörke, M. “How will climate change modify river ﬂow regimes in Europe?” Hydrology Earth System Science, vol. 17, no. 1, pp. 325–339, January 2013. Sipes, J. L. Sustainable solutions for water resources: Policies, planning, design, and implementation. Hoboken, NJ: John Wiley, 2010. Stone, W. W., Gilliom, R. J. and Martin, J. D. “An overview comparing results from two decades of monitoring for pesticides in the Nation’s streams and rivers, 1992–2001 and 2002–2011,” Scientiﬁc Investigations Report US Geological Survey Scientiﬁc Investigations Report 2014–5154, 2014. US Environmental Protection Agency, “National rivers and streams assessment 2008–2009: A collaborative survey,” US Environmental Protection Agency, Washington DC, DC 20460 EPA/841/D-13/001, 2013. US Environmental Protection Agency, “Water Resources,” Climate Change, 15 September 2015. [Online]. Available: http://www3.epa.gov/climatechange/impacts/water.html. [Accessed: 15 October 2015]. US Geological Survey, “A national assessment of changes in Chloride, dissolved solids, and Nitrate in groundwater.” US Department of the Interior, 2014. Walton, B. “The price of water: A comparison of water rates, usage in 30 U.S. cities,” Circle of Blue, 26 April 2010. [Online]. Available: www.circleofblue.org/waternews/2010/world/ the-price-of-water-a-comparison-of-water-rates-usage-in-30-u-s-cities/. [Accessed: 10 October 2015].
2 Characteristics of wastewater Introduction This chapter provides a background on the fundamentals of wastewater treatment including basic chemistry and the characteristics of wastewater, since the next three chapters of this book focus on the treatment of wastewater using constructed wetlands. Readers with experience in wastewater treatment or water chemistry may wish to skip this chapter, but if you are new to topics of water quality improvement, this material will make the following chapters more meaningful. This chapter begins by deﬁning the characteristics of domestic wastewater and the regulatory standards that control the quality of efﬂuent discharges.
Characteristics of raw sewage Although organic matter is the principal contaminant in domestic wastewater, sewage is characterized by the concentration of a number of contaminants or by the weight of the contaminants in a speciﬁc volume of water. The strength of domestic sewage varies depending on the city and country. For example, the per person load in the United States (for biological oxygen demand [BOD], total suspended solids [TSS], total nitrogen and total phosphorous) is signiﬁcantly higher than in Turkey, India, Egypt or Brazil, but better aligned with Denmark and Germany (Henze and Comeau, 2008). Furthermore, the strength of wastewater has changed over time with the advent of the garbage disposal and low-volume toilets and other household appliances. The pH ranges from slightly acidic to moderately alkaline (US Environmental Protection Agency, 2002). Table 2.1 illustrates the range and typical concentrations for a number of components in the United States. To allow systems to be compared around the world, a population equivalent rather than a per person standard has been adopted. This is equal to a volume of 0.2 cubic meters of water and 60 grams of BOD per day. Water is by far the greatest component of domestic sewage. All substances contaminating water amount to only 0.1 per cent of the total volume. This fraction is called total solids; some of these are dissolved (80 per cent) and some are suspended solids (20 per cent). About 65 per cent of the suspended solids will eventually settle but the remaining 35 per cent will not settle out of solution. The contaminants can also be characterized as organic and inorganic. Wastewater from livestock, food processing industries, breweries and domestic sewage is very high in organic matter that is easily biodegradable.
26 CHARACTERISTICS OF WASTEWATER Table 2.1 Characteristics of raw sewage in the United States (US Environmental Protection Agency, 2002)
Mass loading g/p/d
Total suspended solids Biological oxygen demand Total coliform bacteria Faecal coliform bacteria Ammonium-nitrogen, NH4-N Nitrate-nitrogen, NO3-N Total nitrogen Total phosphorus
155–330 mg/L 155–286 mg/L 108–1010 CFU/100 mL 106–108 CFU/100 mL 4–13 mg/L Less than 1 mg/L 26–75 mg/L 6–12 mg/L
250 mg/L 250 mg/L 109 CFU/100 mL 107 CFU/100 mL 10 mg/L Less than 1 mg/L 60 mg/L 10 mg/L
1–3 Less than 1 6–17 1–2
mg/L = milligrams per litre, CFU/100 mL = colony-forming units per 100 millilitres, g/p/d = grams per person per day.
Treatment standards Municipal wastewater is treated to achieve standards described as primary, secondary and tertiary. The compliance standards are established by the US Environmental Protection Agency (EPA) and other national regulatory agencies. Primary treatment is simply the removal of solids through screening or settling. Secondary treatment achieves monthly averages of 30 mg/L or less of BOD and TSS as well as disinfection to remove virtually all pathogenic bacteria. A wastewater treatment facility is also required to remove at least 85 per cent of the initial BOD and TSS. Tertiary or advanced treatment signiﬁcantly reduces the concentrations of nitrate, phosphorous and pharmaceutical contaminants, and generally requires lower concentrations of BOD and TSS than required for secondary efﬂuent. Tertiary treatment might include other measures, such as temperature, depending on the condition of the receiving waters and the presence of sensitive or endangered organisms. The efﬂuent water quality is deﬁned by the discharge permit, which allows some ﬂexibility for the size and type of treatment technology.
Organic matter and nitrogen The organic matter in domestic wastewater is heterogeneous but composed primarily of proteins, carbohydrates and lipids. It contains carbon and is decomposed by bacteria. Bacteria consume oxygen, as they use organic matter for their metabolic processes. Therefore, great quantities of organic matter in a water body can result in a drop in dissolved oxygen (DO). At a DO concentration of 1 mg/L or less, few aquatic organisms can survive. If DO concentrations fall below 5 mg/L (or parts per million), ﬁsh will be unable to live for very long. Trout require at least 8 mg/L of DO, and salmon need around 11 mg/L. This is why removing organic material from sewage is necessary to protect ecosystem and human health. Constructed wetlands and conventional wastewater treatment systems use bacteria to consume organic material, and this occurs in either oxygen-rich or low-oxygen environments, although it occurs more rapidly under aerobic conditions. The amount of organic material in a sample of water is indirectly measured by determining how much oxygen is consumed within a given amount of time (Figure 2.1). This characteristic is called biological oxygen demand or BOD. Tests of BOD
CHARACTERISTICS OF WASTEWATER 27
Figure 2.1 BOD tests of wastewater samples. Photo: SuSanA Secretariat. License: CC-BY-SA-3.0.
are generally based on a ﬁve-day time period (BOD5), but seven-day and ultimate (about 20 days) tests are sometimes reported in the literature. Efﬂuent discharge permits establish maximum and monthly average BOD levels for treated water ﬂowing into streams and other water bodies. Understanding the transformational sequence of organic nitrogen (organic matter) and various types of nitrogen is critical to understanding the purposes and design features of the various kinds of constructed wetlands used for water quality improvement. Nitrogen, like carbon, is an essential element of organisms, but nitrogen in the form of ammonia and nitrite is toxic to aquatic organisms at high concentrations. The removal of organic matter and nitrogen is a primary goal of wastewater treatment. Organic matter is transformed through bacterial activity into ammonia, nitrate and then nitrogen gas. This is done in three stages called ammoniﬁcation, nitriﬁcation and denitriﬁcation. Organic nitrogen is transformed into ammonia (there are two forms: ammonia, NH3 and ammonium, NH4) by microbial decomposition in either an oxygen-rich or oxygen-depleted environment. After ammoniﬁcation, populations of bacteria convert ammonia to nitrite, NO2, and then to nitrate, NO3 (nitriﬁcation). This process occurs primarily in an oxygen-rich setting. Finally, other genera of bacteria convert the nitrate to harmless nitrogen gas (denitriﬁcation). Although a wastewater treatment system might convert almost all of the organic matter to ammonia or nitrate, the amount of total nitrogen in the wastewater might not change much. This is because organic matter, ammonia and nitrate are all forms of nitrogen. Total nitrogen decreases signiﬁcantly only when the transformations reach the stage of creating nitrogen gas (denitriﬁcation). In addition to total nitrogen, measurements of total Kjeldahl nitrogen (TKN) are also common. TKN is the combination of organic nitrogen, ammonia and ammonium but not nitrite or nitrate.
Total suspended solids The second fundamental indicator of water quality is also an indirect measurement. TSS are particles that do not settle from a sample of wastewater and cause the water
28 CHARACTERISTICS OF WASTEWATER
to appear cloudy. There is a high correlation between TSS and pathogenic bacteria in wastewater and heavy metals in stormwater.
Phosphorous In wastewater, phosphorous exists in two forms. Organic phosphorus is combined with organic matter, while inorganic phosphorous is found as either orthophosphates or polyphosphates. Furthermore, phosphorous can be in either dissolved or solid states. Like excess nitrogen, excess phosphorus in natural water bodies causes algae bloom and precipitous drops in DO that can kill populations of ﬁsh and other organisms.
Pathogens There are many potential disease-causing organisms in domestic sewage including bacteria, protozoa and viruses. Indicators of pathogens may be used to estimate their presence rather than testing for speciﬁc organisms. For example, coliform bacteria are a very large group of species, only some of which cause disease in humans. However, since the correlation of disease-causing organisms is highly correlated with levels of coliform bacteria, they are used as a guide. Faecal coliform bacteria are a smaller category of bacteria and are often used as a test. The presence and quantity of speciﬁc species, such as Escherichia coli (E. coli), are sometimes identiﬁed, but the information about individual species is almost always used to indicate the presence or absence of many other disease causing organisms. The current EPA E. coli recommendation for primary recreational use (swimming and wading) is fewer than 126 colonies/100 mL. Enterococci, another genus of bacteria pathogen, has a primary recreation standard of 30 colonies/100 mL.
Conventional wastewater treatment plants In metropolitan areas, highly engineered wastewater treatment plants rapidly treat great volumes of sewage (Figure 2.2). Activated sludge processes are the most common methods used. This process adds large quantities of bacteria from sewage sludge to raw wastewater. A sequence of process steps requiring aeration, mixing and moving water through a series of tanks improves the water quality by removing organic nitrogen, pathogens and suspended solids. This requires many large pumps to aerate, mix and move the water. The rapid treatment of large volumes of water in a small land area is possible through the application of very high capital and operation costs. Highly skilled personnel and the abundant use of chemicals are other factors necessary to support conventional wastewater treatment plants.
Decentralized wastewater treatment However, for small towns and cities, lower capital and operation costs and very little need for chemicals or trained personnel is an option presented by constructed wetlands. In fact, tens of thousands of small towns in Europe rely on constructed wetlands to produce wastewater efﬂuent with similar or better quality compared to their big city counterparts. Since constructed wetlands can be created as a decentralized technology, new wetlands can be created for each new neighbourhood just before it is constructed.
CHARACTERISTICS OF WASTEWATER 29
Figure 2.2 Conventional wastewater treatment plants are highly engineered facilities that require sophisticated operation controls. They require large capital investments as well as substantial annual energy, operation and maintenance budgets. In this image, a large pump powers an aeration device to increase the oxygen content of the water and support bacteria that consume organic matter. Photo: The Chesapeake Bay Program. License: CC-BY-NC 2.0.
For the individual home or group of homes or for institutions, constructed wetlands create a more effective and reliable alternative to the leach ﬁeld common in rural America.
Sewage lagoons Every constructed wetland, as well as every conventional wastewater treatment plant, is preceded by a pretreatment step that may be as simple as a series of screens and grit chambers or more capable as an effective water quality improvement stage, such as a multi-chamber septic tank. Small towns comprising a few thousand people often use aerated or facultative lagoons as the pretreatment step (or the only treatment) for domestic sewage. Facultative lagoons are 4–8-feet-deep sewage ponds that are not mechanically mixed or aerated, where raw sewage is held for as long as a month. In very cold winter areas, sometimes three or four months’ worth of sewage is stored in these ponds until spring. Three zones are created in the facultative lagoon. The top layer of water is oxygen rich (aerobic) due to contact with the atmosphere, while the bottom layer is anaerobic and contains sludge that settles due to gravity. The middle zone (the facultative zone) has a reduced oxygen concentration (anoxic) and is populated by organisms that can ﬂourish in a range of oxygen concentrations. These microorganisms are called facultative, as they have the capacity to survive in various oxygen environments. Facultative lagoons are characterized by rapid algae growth, objectionable odours (especially when wind or temperature inversions cause the lagoon layers to
30 CHARACTERISTICS OF WASTEWATER Table 2.2 Typical septic tank effluent concentrations (US Environmental Protection Agency, 2002; Crites et al., 2014)
Total suspended solids, TSS Biochemical oxygen demand, BOD Faecal coliform bacteria Ammonium-nitrogen, NH4-N Nitrate-nitrogen, NO3-N Total nitrogen Total phosphorus
36–85 mg/L 118–189 mg/L 106–107 CFU/100 mL 30–50 mg/L 0–10 mg/L 29.5–63.4 mg/L 8.1–8.2 mg/L
60 mg/L 120 mg/L 106 CFU/100 mL 40 mg/L 0 mg/L 60 mg/L 8.1 mg/L
mg/L = milligrams per litre, CFU/100 mL = colony-forming units per 100 millilitres.
mix) and large land requirements. Therefore, they are invariably fenced to prevent public access and isolated from residential areas. Aerated lagoons require pumps to deliver air to the bottom of the ponds. The oxygenated water becomes the environment for aerobic bacteria that consume organic matter. The aerobic process is faster but requires energy inputs and performance declines in cold weather.
Septic tanks In contrast, septic tanks are airtight and are usually placed below ground. Since there is no possibility of public contact with contaminated water and a useful landscape can be installed above the underground tank, they are well suited to public areas and as a pretreatment stage for subsurface wetlands. Since they are below ground, they are somewhat insulated from cold weather. They can also be installed with passive solar windows to raise the temperature inside the tank. Water is held in septic tanks for 12 hours to a few days, and conditions are anoxic or anaerobic. Modern septic tanks signiﬁcantly improve the quality of the efﬂuent (outﬂow) in comparison to the raw sewage inﬂow. Septic tanks improve water quality signiﬁcantly as illustrated by a comparison of the concentrations in Tables 2.1 and 2.2. The pH range for septic tank efﬂuent is 6.4–7.8 with an average of 6.5 (slightly acidic) (US Environmental Protection Agency, 2002).
References Crites, R. W., Middlebrooks, E. J., Bastian, R. K. and Reed, S. C. Natural wastewater treatment systems, Second edition. Boca Raton: IWA, CRC Press, Taylor & Francis Group, 2014. Henze, M. and Comeau, Y. “Wastewater characterization,” in Biological wastewater treatment: Principles, modelling and design, London: IWA, 2008, pp. 33–52. US Environmental Protection Agency, “Onsite wastewater treatment systems manual,” EPA/625/R-00/008, 2002.
3 Free water surface constructed wetlands Introduction This and the next two chapters introduce three types of constructed wetlands. The designs and treatment performance presented for these wetlands are based on remediation of domestic or municipal wastewater, because this is the original purpose for each. Furthermore, this will provide a common basis for comparing the capability of each wetland type.
Engineered free water surface wetlands Free water surface wetlands are engineered treatment landscapes, but they are very similar in appearance to naturally occurring marshes (Figure 3.1). The wetland shown in Figure 3.2 is a man-made landscape to treat non-point source pollution from stormwater run-off. The variety of plants and the presence of open water make these very attractive places of interest to people as recreation and education sites and to wildlife for shelter, food and water.
Figure 3.1 This wastewater treatment plant uses free water surface wetlands (six cells of deep and shallow marsh) to reduce nitrogen and phosphorus levels to meet very high water quality discharge standards. Blue Heron Water Reclamation Facility, Titusville, Florida. Photo: Google Earth 28°32′25.03″ N 80°51′37.83″ W, image date: 13 February 2014, image accessed: 23 October 2015.
32 FREE WATER SURFACE CONSTRUCTED WETLANDS
Figure 3.2 Although engineered landscapes, free water surface constructed wetlands, such as this one to treat stormwater, mimic natural wetlands. Therefore, careful attention to planting local native species will yield results that reduce maintenance and enhance treatment performance. Photo: Wendy Patoprsty. License: reproduced with permission.
Experiments with free water surface wetlands in the United States for the treatment and disposal of municipal sewage began over 100 years ago when partially treated sewage was discharged into natural wetlands. The ﬁrst artiﬁcial free water surface wetland designed to treat sewage was built in the Netherlands in 1967. While it was effective, the design required a considerable amount of space. In the United States, during the 1970s, experiments yielded engineered constructed wetlands for wastewater treatment. Although the Europeans focused on the development of the horizontal subsurface ﬂow wetland as the preferred treatment wetland type, in America the free water surface type became the most common constructed wetland (Kadlec, 2009a). In the United States, these wetlands are most often used to treat secondary efﬂuent from conventional wastewater treatment plants to achieve advanced (tertiary) water quality (Figure 3.3). This wetland type is also most common for the treatment of stormwater run-off. Stormwater wetlands are discussed in another chapter. There are now hundreds of free water surface wetlands for tertiary treatment in the United States, and some of them are very large (Figure 3.9). For example, a free water surface treatment wetland in Orlando, Florida, is about 1,235 acres (500 hectares) (Kadlec, 2009b).
Design challenge From a sustainable development perspective, the primary challenge in the design of free water surface wetlands for domestic sewage or livestock wastewater treatment is providing secondary uses simultaneously. Compared to the subsurface ﬂow wetland types, the potential of free water surface treatment wetlands to provide recreation, education and wildlife beneﬁts is much greater. However, the public must be protected
FREE WATER SURFACE CONSTRUCTED WETLANDS 33 Figure 3.3 The inflow from the wastewater treatment plant across the width of the shallow marsh wetland at the Blue Heron Water Reclamation Facility. Photo: Matt Hixson. License: reproduced with permission.
Figure 3.4 Water from septic tanks, sewage lagoons or wastewater treatment plant secondary effluent (as in this case) is often oxygen depleted. Aerating the inflow with an artificial or naturalistic cascade adds the oxygen necessary for rapid biological removal of contaminants. Photo: Gary Austin, 2013.
from contacting water that has pathogenic bacteria in excess of US Environmental Protection Agency (EPA) standards for primary (swimming) or more commonly secondary (boating and ﬁshing) recreational use. Consequently, free water surface wetlands are rarely used to treat primary efﬂuent from septic tanks or sewage lagoons due to odour and contact hazards. Instead, they are employed to raise the quality of water from secondary to tertiary standards by treating secondary efﬂuent (Figure 3.4). A second challenge is creating designs where the water ﬂows uniformly through the wetland to make optimum use of the treatment capacity and maintain a small footprint. Mosquito control and wildlife use are also challenges but more manageable ones.
Pretreatment Extending the longevity of the treatment wetland and reducing the organic load that is applied are the purposes of pretreatment of domestic sewage. In rural communities, this is often accomplished in facultative or aerated sewage lagoons, but a septic tank or Imhoff tank are better pretreatment solutions.
34 FREE WATER SURFACE CONSTRUCTED WETLANDS Figure 3.5 The design for a free water surface wetland includes a distribution pipe with cleanouts, a deep inflow trench or pool, water depth varying between 12 inches and 30 inches, and dense emergent vegetation perpendicular to the flow direction. Image: Zhenyu Liu and Gary Austin.
Typical configuration The general design of a free water surface wetland includes a deep-water pool or trench at the wetland inlet and outlet (Figure 3.5). Then the wastewater ﬂows on the surface through dense stands of emergent vegetation. The depth of the water in these emergent marshes may vary from about 12 inches to about 30 inches to encourage the growth of a variety of plant species. Sometimes areas of open water 3–6 feet deep are incorporated into the design. If the wetland is large, it is usually divided into a sequence of cells in order to collect and redistribute the water uniformly. The wetland is generally sealed with a high-density polyethylene (HDPE) liner or clay inﬁltration barrier. Treated water ﬂows into an outlet structure with an adjustable pipe that controls the water level within the wetland. This is adjusted to control weeds or respond to extremely cold weather. If there are high levels of pathogenic bacteria in the water, then the wetland is fenced to prohibit human access, but where secondary efﬂuent has been chlorinated or otherwise disinfected before reaching the constructed wetland, then public access might be permitted (Figure 3.11) (Crites, 2001).
Sizing Monitoring the performance of existing free water surface wetlands for the treatment of domestic sewage has established a sizing rule of 48 to 54 square feet (4.5–5 m2) per person to accomplish secondary treatment standards (Cooper, 2009). This equals about 1 acre (0.4 hectare) for every 850 people the system serves. For accurate wetland sizing, matched to target contaminants or nutrient reduction, communities should consult an environmental engineer.
Loading In order to achieve 30 mg/L for biological oxygen demand (BOD) and total suspended solids (TSS) in the efﬂuent of a free water surface treatment wetland, the recommended aerial loading is 6 grams per m2 and 7 grams per m2, respectively. The standard of 30 mg/L for BOD and TSS is the basis for secondary efﬂuent in the United States. An aerial load of 1.5 grams per m2 of total Kjeldahl nitrogen (organic nitrogen and ammonia [TKN]) should yield a 10 mg/L concentration in the wetland efﬂuent. Phosphorus in domestic wastewater ranges from 4 to 12 mg/L, and little improvement can be expected if aerial loading is 0.4 grams per m2 or more. If loading of faecal coliform bacteria is more than 10,000 colony-forming units (CFU) per 100 mL, then
FREE WATER SURFACE CONSTRUCTED WETLANDS 35
it is unlikely that the efﬂuent will meet secondary recreation standards (200 CFU/100 mL). A hydraulic residency time of 3 days is typically required for a 2 log reduction in bacteria (Wallace, 2006).
Hydraulic loading rate For domestic and municipal sewage applications, the amount of water that the wetland receives is generally determined by the BOD aerial loading criteria noted above. The amount of water associated with the BOD varies. Water use per person in the United States is much higher than in Europe and developed countries in Asia. Per person water use in developing countries is much lower than use in Europe. The average water use inﬂuences the hydraulic loading rate of the wetland (and hydraulic residency time). In the United States, 4 cm (1.6 inches) to 10 cm (3.9 inches) per day is a common range for hydraulic loading (Wu et al., 2015). Therefore, if the hydraulic loading is 3.5 inches of water added to a 1-acre wetland, this equals 95,000 gallons of capacity per day. If the wetland receives ﬂow from combined stormwater and sanitary sewers, then the amount of water increases and concentration of BOD decreases, although the BOD load is the same. This situation results in water moving more rapidly through the wetland in the high ﬂow condition, and there is less time for bacteria and other mechanisms to remove BOD and other contaminants. Recycling some of the treated wastewater to the beginning of the wetland is sometimes recommended where the concentration of BOD is very high and the volume of the water inﬂow is low. This would dilute the BOD concentration to levels compatible with the cultural needs of the wetland plants.
Cell shape Initial experiments in the Netherlands led to long narrow wetlands with berms between them to facilitate harvesting the wetland plants. This conﬁguration doubled the land area required and was not the optimum shape for treatment effectiveness. Free water surface wetlands are particularly troubled by the creation of preferential pathways by the water ﬂowing through them. Therefore, the water ﬂows through more rapidly and with less contact with the plant stems and bottom surface than intended. To compensate, the wetland is usually divided into two or more roughly square or rectangular treatment cells to shorten the ﬂow length and allow the water to be collected and redistributed evenly across the width of the cells.
Depth The water in free water surface wetlands generally has high levels of dissolved oxygen but this declines at the bottom of the treatment pool. A variety of oxygen levels is generally beneﬁcial, as some contaminants or excess nutrients are removed more effectively in one condition or another. However, treatment wetlands deeper than 3 feet limit the growth of almost all emergent plants (Figure 3.6), which might be replaced with ﬂoating leaf plants, such as water lilies, or ﬂoating plants, such as duck weed, or open water. In most designs, the water depth is 16–24 inches (15–60 cm).
36 FREE WATER SURFACE CONSTRUCTED WETLANDS Figure 3.6 Differing water depths encourage a variety of species to flourish, and increase the ecosystem benefits of the artificial wetland. Ideally, the vegetation is planted in bands perpendicular to the flow direction of the wastewater. This improves uniform distribution, retention time and treatment performance. Photo: Gary Austin, 2014.
Materials Waterproof membrane Preventing inﬁltration of contaminated water can be accomplished with synthetic liners or clay. Free water surface wetlands for tertiary treatment of efﬂuent from conventional wastewater treatment plants are often very large. Therefore, the cost of synthetic liners is avoided where possible through the use of bentonite or other clay barriers covered by wetland soil. The compacted depth of a bentonite layer is about 12 inches (30 cm) and may be an economic alternative to synthetic liners if the bentonite source is near the proposed wetland. Bentonite is mined in Wyoming in the United States. When seasonal groundwater is well below the bottom of the wetland, then the US EPA permits a clay barrier if inﬁltration can be limited to 10–6 cm per second (Kadlec, 2009b). Synthetic liners are made of polyvinyl chloride (PVC) or HDPE or other compounds such as polypropylene. PVC, at least 30 mil (0.76 mm), is generally the least expensive and is suitable if not exposed to sunlight. HDPE should be at least 40 mil (1 mm) and is about 10 per cent costlier than PVC. Liners with an embedded nylon or other netting are available where great strength is necessary. When either a clay or synthetic liner is used, a layer of wetland soil 12 inches (30 cm) deep on top of the liner will support tall emergent plants (Kadlec, 2009b).
Inlet/outlet Generally, a deep 6-feet wide (2 m) trench at the inlet of each free water surface treatment cell is necessary to collect sediment and to uniformly distribute the inﬂuent (Figure 3.5). In practice, many inlet designs are used, including discharge onto a rock slope above the wetland. However, distribution of water continuously along the entire face of the wetland through perforated pipes or other methods leads to more uniform ﬂow and positive treatment results. Similarly, a continuous collection of the efﬂuent from each cell rather than a single outlet point will encourage uniform ﬂow (Figure 3.7). Two or more small treatment cells rather than one large cell where water is
FREE WATER SURFACE CONSTRUCTED WETLANDS 37 Figure 3.7 This below ground view shows the wetland cell outlet trench with its perforated collection pipe. The outlet vault includes a vertical pipe that can be adjusted to establish the level of the water in the wetland. Image: Zhenyu Liu and Gary Austin, 2016.
distributed and collected as described above will yield the best treatment result. Where the public has access to the wetland, care must be taken to provide safe conditions. Therefore, limiting slopes to 3:1 or ﬂatter and water depth to 3 feet, or other measures to prevent visitors from falling into deep water, are necessary.
Filter media In free water surface wetlands, the stems of the vegetation serve as the ﬁlter media causing sedimentation. Dense vegetation should be planted in strips or masses perpendicular to the direction of water ﬂow. Bacteria on the plant stems and in the top layer of soil and organic material on the bottom of the wetland convert organic material to ammonia, and ammonia to nitrate.
Cold weather applications Free water surface wetlands have been implemented successfully for the treatment of domestic sewage in northern United States and southern Canada, where the average annual temperature is about 44.6°F (7°C) or higher (Kadlec, 2009b). However, operation in freezing weather requires active management of the system to create an air space below a layer of ice or insulation of the wetland with mulch on top of the ice. The size of the wetland must be larger in cold climates in order to meet treatment standards in winter.
Clogging Even very dense stands of emergent vegetation in a free water surface wetland are very porous, allowing water to move freely through the plants. In fact, uniform ﬂow is a more important issue than it is with other wetland types, as the water readily ﬁnds the most open route through the wetland. Accumulation of sediment and detritus in the free water surface wetland diminishes its maximum volume and somewhat shortens its life; therefore, good pretreatment is necessary.
38 FREE WATER SURFACE CONSTRUCTED WETLANDS
Site-scale application An example of the uncommon use of a free water surface wetland for the treatment of septic tank efﬂuent is a three-cell wetland treating wastewater (toilet and sink) from 300 people in a university building. The wetland was constructed in Taiwan at the National Cheng-Kung University and began operation in November 2003. The treatment wetland is composed of two free water treatment cells and an ornamental pond (Figure 3.8). A ﬁlter and a storage tank to facilitate water reuse follow these basins (Ou et al., 2006). Local soil 30 cm deep over an impermeable liner supports cattail (Typha orientalis) (half of cell C, and cell D, Figure 3.8) and water hyacinth (Eichhornia crassipes) in the second half of the ﬁrst basin (C). The water in the ornamental pond is between 6 inches (15 cm) and 33.5 inches (85 cm) deep, and contains umbrella papyrus (Cyperus alternifolius), hayata (Hygrophila pogonocalyx), yellow water lily (Nuphar shimadai), water primrose (Ludwigia adscendens) and tropical sundew (Drosera burmanni) (Ou et al., 2006). The hydraulic loading rate is 4.2 cm per day (which is higher than the typical rate), which yields a residency time of 6 days. In the septic tank efﬂuent, the level of organic matter and ammonia was high (9.6–154.7 mg/L TKN) but nitrate was low (0.05 mg/L). The treatment system resulted in low levels of TSS, BOD and chemical oxygen demand (COD), and good performance for the reduction of total phosphorus and pathogenic bacteria (Table 3.1). Initially, 53.1 per cent of nitrogen was organic, while 46.5 per cent was ammonia. The treatment cells demonstrated effective ammoniﬁcation and nitriﬁcation as indicated by the increase in nitrate and nitrite to as much as 25.9 mg/L. The level of nitrite and nitrate dropped from 25.9 to 13.68 mg/L in the ﬁnal efﬂuent, indicating that some denitriﬁcation occurred, although nitrate in the ﬁnal efﬂuent remained high. Since the concentration of nitrate was high in the efﬂuent, the reduction in total nitrogen was moderate (42.3 per cent). The remaining concentration of TKN (organic nitrogen and ammonia) in the efﬂuent also indicates incomplete nitrogen removal. The ornamental basin had a signiﬁcant impact on the improvement of water quality especially with regard to BOD, nitrate, TKN, total nitrogen, total phosphorus and total coliform bacteria (Ou et al., 2006). Recycling a portion of the treated efﬂuent to the septic tank would probably reduce the nitrate and total nitrogen in the ﬁnal efﬂuent. The ﬁrst cell (C in Figure 3.8) was fenced to prevent public access, but the remaining two cells were available. In the efﬂuent of the second cell (D), the E. coli
Figure 3.8 Plan view diagram of the constructed wetland sequence at the architecture building at National Cheng-Kung University. The sequence wraps around university buildings. The ornamental pool (E) fills a narrow space between buildings. A – Septic tank; B – Pump vault; C – Cell 1; D – Cell 2; E – Ornamental pond; F – Slag filter; G – Storage tank (Ou et al., 2006). Image: Gary Austin adapted from W. S. Ou et al. (2006).
FREE WATER SURFACE CONSTRUCTED WETLANDS 39 Table 3.1 Mean concentrations (mg/L) and per cent removal of contaminants in a free water surface treatment wetland in Taiwan (Ou et al., 2006)
Influent Effluent % removal
63.1 16.4 74.5
94 16.5 83
198.5 60.4 65.9
81.8 20.4 72.3
0.05 13.68 –
82.1 35 42.3
14.5 4.2 69.8
8,964 2,258 947 UD 78.5 >99.9
TSS = total suspended solids, BOD = biological oxygen demand, COD = chemical oxygen demand, TKN = total Kjeldahl nitrogen (organic nitrogen and ammonia), NOx = nitrite and nitrate, TN = total nitrogen, TC = total faecal coliform bacteria, EC = Escherichia coli bacteria.
concentration was 6 CFU/100 mL and not detectable in the water of the ornamental pond. The US EPA standard for primary recreation contact is 126 CFU/100 mL. Therefore, public access to the second and third cells is warranted. Mosquitos in the wetland were controlled by introducing ﬁsh (Macropodus opercularis) that prey on mosquito larva (Ou et al., 2006). The ﬁrst two cells of the university free water wetland achieved US EPA secondary efﬂuent standards. The third cell planted with ornamental wetland plants provided a campus amenity, while providing some tertiary water quality beneﬁts. The treated water was reused in the drip irrigation system for the campus landscape (Ou et al., 2006). Since the water is reused for irrigation, the residual nitrate is a beneﬁt to plant growth and reduced the need for artiﬁcial fertilizer.
Large-scale tertiary treatment applications The E L Huie Jr Constructed Treatment Wetlands in Georgia are used to treat secondary efﬂuent from a conventional wastewater treatment plant to a high standard. The Huie free water surface wetland, shown in Figure 3.9, includes several parallel sequences of treatment cells within the 263 acres of constructed marsh. The tertiary treatment allows the water to be delivered to drinking water supply reservoirs. The amount of water reclaimed (17.4 million gallons per day or MGD) approaches the amount used (25 MGD) by the customers in the wastewater treatment district (Jarrin, 2012). The US EPA established discharge concentration maximums for the Huie wetlands (Table 3.2). The actual concentration is well below the compliance standards. The estimated residence time of water through the wetland and reservoirs before reuse is 1 year under drought conditions and 2 years under normal supply and withdrawal conditions (Jarrin, 2012). Since the water entering the Huie wetland has been disinfected as a ﬁnal step at the conventional wastewater treatment plant, the constructed wetlands are a resource for wildlife and the public. In fact, there is a visitor centre dedicated to providing information and tours to view and interpret the wetland ecosystem and wildlife.
Retrofit and rural applications Rural communities often use sewage lagoons for treatment of wastewater. These are generally inefﬁcient and consume large land areas. The town of Cle Elum, Washington (2,300 people), used three aerated lagoons, but these often failed to meet the discharge
40 FREE WATER SURFACE CONSTRUCTED WETLANDS
Figure 3.9 The E L Huie Jr Constructed Treatment Wetlands in Clayton County, Georgia, USA, have the capacity to treat more than 17 MGD to tertiary standards. Photo: Google Earth, 33°29′11.05″ N 84°17′50.82″ W, image date: 5 June 2014, image accessed: 10 August 2015.
Table 3.2 Water quality standards and performance of the E L Huie Treatment Wetlands
NPDES limit mg/L monthly/weekly average
Actual mg/L (2011 average)
BOD TSS NH3 TP
10/15 30/45 1.4/2.1 0.6 (1)
3 5 0.06 0.24
1 – Annual average at the lake discharge.
standards for secondary efﬂuent. In order to improve compliance, the third sewage lagoon was converted into a free water constructed wetland, which was inaccessible to the public. The new ﬁve-acre wetland was divided into three planted marsh sections by two 3-feet deep (1 m) open water trenches. The water level above the planted beds was maintained at 18 inches (46 cm) in summer and increased to 24 inches (61 cm) in winter to accommodate a layer of ice in this cold climate (latitude 47°N) (Crites, 2001). The original lagoon received 24 inches of ﬁll, a 6 inch depth (15 cm) of 3⁄4 inch (19 mm) minus, non-angular gravel and an HDPE liner and then another 6 inch depth of gravel over the liner. This formed the bottom of the open-water zones. The marsh beds received an additional 12 inches (30.5 cm) of soil ﬁll topped by a 6-inch layer of planting media (half soil ﬁll and half sewage sludge). The three marsh sections were planted with hard-stem bulrush (Scripus acutus) and represented 68 per cent of the wetland area. The deep-water strips increased water retention time and discouraged short circuit ﬂows by redistributing water evenly across the width of the wetland.
FREE WATER SURFACE CONSTRUCTED WETLANDS 41
Performance of the system for BOD and TSS was outstanding. Inﬂuent BOD (182 mg/L at the ﬁrst lagoon inlet) was reduced 96 per cent to 6.4 mg/L. Inﬂuent TSS (169 mg/L at the lagoon inlet) were reduced 98 per cent to 3 mg/L at the wetland outﬂow. The level of dissolved oxygen at the constructed wetland outfall averaged a healthy 6.9 mg/L (Crites, 2001) compared to minimum levels of 0.2–0.6 mg/L required for conversion of organic matter to ammonium and the conversion of ammonium to nitrate (Zhang, 2010).
The Talking Water Gardens case study The Albany–Millersburg conventional wastewater treatment plant, in cooperation with an industrial user, recently constructed a free water surface wetland to achieve improved water quality (Figure 3.10). The site was formerly a lumber mill. Designed by CH2M Hill and Kurisu International, the wetland is located in Albany, Oregon (USA), and discharges to the Willamette River (Figure 3.11). The Talking Water Gardens project is a public–private partnership where the $13.75 million cost was shared by the cities, state and industry. An additional $5 million is planned for visitor amenities. The Willamette River has a Total Maximum Daily Load (TMDL) for temperature, bacteria and mercury reduction required by the Oregon Department of Environmental Quality. Of particular concern is the temperature of the river, where cooler water is
Figure 3.10 This free water surface constructed wetland in Albany, Oregon, like the Huie wetland, treats secondary effluent to meet tertiary standards. It is also a popular public park and tourist attraction. The lush wetland vegetation, extensive walking trails and the many bird species draw many visitors to the Talking Water Gardens. Photo: Gary Austin, 2014.
42 FREE WATER SURFACE CONSTRUCTED WETLANDS Figure 3.11 Talking Waters Garden in Albany, Oregon. The Willamette River is on the upper left, and the wastewater treatment plant and metal industry are at the bottom of the image. The wetland is divided into 10 basins and six individual flow paths. The berms between the basins form an extensive pedestrian network. Photo: Google Earth, 44°38′47.12″ N 123°04′02.83″ W, image date: 14 July 2014, image accessed: 31 August 2015.
Figure 3.12 Deep water zones at the Talking Water Gardens project increase residence time and cool the wastewater effluent before it is discharged into the Willamette River. Photo: Gary Austin, 2014.
FREE WATER SURFACE CONSTRUCTED WETLANDS 43
required for certain salmon and trout species for rearing and migration in the stretch of the river by Albany. The Talking Water Gardens was built to address the temperature and heat load reduction of the treated efﬂuent from the wastewater treatment plant and the industrial user (Figure 3.12). The option of the constructed wetland, rather than other mechanical cooling options, such as cooling towers and refrigeration, was selected partly due to lower cost and other beneﬁts, such as improving habitat and creating public amenities. In addition to temperature reduction, water quality is improved with the mixing and aeration of the water in the wetland. Other pollutants and nitrogen and phosphorous levels are also reduced through biological treatment and sedimentation (US Environmental Protection Agency, 2012) (Figure 3.13). The free water surface wetlands constructed in Albany treats a maximum of 9.6 MGD of efﬂuent from the Albany–Millersburg wastewater treatment plant and an additional 3 MGD of treated efﬂuent from the ATI Wah Chang metal manufacturing plant. The treated efﬂuent from this industry is characterized by high total dissolved solids and is fully blended with the Albany treated efﬂuent. The wetlands occupy 39 acres of the 50-acre site. The remaining land is dedicated to public trails and other user amenities and wildlife habitat. The water averages a detention time of two days. Several years after construction, the wetland is still growing to achieve the plant coverage needed for shade and heat load reduction. Often, free water surface wetlands are used to achieve tertiary quality efﬂuent, so they can generally be accessible to the public without concern for contact with pathogenic bacteria. The great advantages of free water surface treatment wetlands are the ancillary recreation, education, scenic and wildlife beneﬁts that can be achieved using careful design (Figure 3.14). In the case of the Talking Water Gardens, which is open every day to the public, thousands of visitors, bird watchers and photographers come each year to walk the trails and view wildlife and wetland scenery. Organized activities include tours with professional groups, hosted events including track meets and volunteer activities. Talking Water Gardens was built as a ‘living laboratory’ to bring wetland science to life for school grades from kindergarten through high school as well as for university students. Educational programmes, such as student tours, ﬁeld day events and wetland habitat research, occur throughout the year (Neal and Preston, 2015).
Figure 3.13 Several cells of the treatment wetland are shown in this panoramic view. In the foreground is a deep pool covered with floating vegetation (Azolla sp.). The vegetation shades the water and prevents heat gain. Azolla is an effective accumulator of lead, cadmium, nickel and zinc. It can be harvested and used as a green fertilizer. A heavy mat can be detrimental to submerged plants and other aquatic organisms. Photo: Gary Austin, 2014.
44 FREE WATER SURFACE CONSTRUCTED WETLANDS Table 3.3 Official visitors (Neal and Preston, 2015)
2010–2011 2011–2012 2012–2013 2013–2014
497 986 1,627 1,372
The Talking Water Gardens staff keeps track of numbers of some types of visitors. The visitors who come to the garden for professional involvement, public outreach, events, volunteer opportunities or education since construction began in 2010 are shown in Table 3.3. However, the garden staff does not count the numbers of informal visitors from the public. It is likely that their numbers are far greater than those visitors that come in groups for events (Neal and Preston, 2015). The wetland park includes cells 1–5 feet deep (Figure 3.12) and nine waterfalls (Figure 3.14) and weirs to aerate and mix the water. In addition to meeting the more stringent TDML standards, the wetlands make other water quality improvements. They will remove lead and nickel below the most restrictive regulatory limit (81 per cent and 94 per cent, respectively). Sixty per cent more BOD will be removed than is required by regulations, and chromium, zinc, mercury, oil and grease levels will also be below the most restrictive regulatory limits (US Environmental Protection Agency, 2012). The amount of nitrogen in the sewage and industrial inﬂuent is high primarily due to nitrate (Table 3.4). There are three points where treated wastewater enters the wetland. The north inﬂuent point is associated with industrial wastewater and is characterized by higher concentrations of ammonia and nitrate. All of the wetland efﬂuent discharges from a single point. The constructed wetland removal of ammonia
Figure 3.14 The aeration of the wastewater entering the wetland from the wastewater treatment plant is artfully done to enhance the naturalistic park-like setting. Photo: Gary Austin, 2014.
FREE WATER SURFACE CONSTRUCTED WETLANDS 45 Table 3.4 Ammonia and nitrogen removal (mg/L) (Frazier, 2012)
North influent East influent South influent Final effluent
3.5 2.7 2.1 1.7
10.1 10 9.2 8.8
0.9 0.5 0.6 99 89 99
Personal care products Tonalide Oxybenzone Triclosan
0.24 LOD 0.05
0.11 LOD 0.05
0.05 LOD 0.04
0.02 LOD 0.03
90 – 79
0.33 LOD 0.13
Endocrine-disrupting compounds Bisphenol A 3.90 Ethinylestradiol LOD LOD = less than the limit of detection.
It is signiﬁcant that the resulting outstanding water quality was achieved without artiﬁcial aeration, pumping or use of chemicals. When hybrid wetlands are installed on a gently sloping site, gravity can be used to transfer the water between treatment stages. An experimental hybrid wetland with three stages constructed to achieve tertiary water quality conﬁrms the experience from the wetland presented above. The experimental wetland was composed of a fully saturated vertical subsurface ﬂow cell followed by a free-draining, vertical subsurface ﬂow cell. The third cell was a horizontal subsurface ﬂow bed. Fifty per cent of the efﬂuent from stage two was pumped to stage one for denitriﬁcation (Vymazal and Kröpfelová, 2011). The organic load was 17.8 grams per day of BOD, compared to the 9 grams per day in the Spanish hybrid wetland described above. Nevertheless, the performance was very similar. The average removal rates were: BOD – 94.5 per cent (10 mg/L), TSS – 88.5 per cent (9.2 mg/L), ammonia – 78.3 per cent (6.5 mg/L) and phosphorus
Figure 6.5 The storage tank that receives the treated effluent from the free water surface stage provided unexpected water quality improvement. There was a significant decrease in the levels of E. coli due to the penetration of sunlight to the bottom of the tank. Photo: Centre for New Water Technologies, R & D & I, 2014. License: reproduced with permission of CENTA.
94 HYBRID CONSTRUCTED WETLANDS
– 65.4 per cent (1.8 mg/L). The concentration of nitrates in the outﬂow was only 1.1 mg/L. The combined ammonia and nitrate removal was 73.5 per cent (Vymazal and Kröpfelová, 2011).
Hybrid wetland treating surface run-off An example of a hybrid treatment wetland applied to the problem of surface run-off from livestock operations was designed by Blumberg Engineers and constructed in 2013. The hybrid wetland in Hennersdorf, Germany (Figure 6.6), treats stormwater contaminated with agricultural waste from a cattle operation, including run-off from silage production. The treatment sequence includes four stages: (1) ﬂoating wetlands over a sedimentation pond 4,445 square feet (413 m2); (2) a buffer pond 4,747 square feet (441 m2); (3) a vertical subsurface ﬂow wetland 10,900 square feet (1,014 m2); (4) a horizontal subsurface ﬂow wetland 5,513 square feet (475 m2). The concentration of organic matter in the wastewater varies but is very high, between 3,400 mg/L and 32,700 mg/L COD with a maximum ﬂow of 7,925 gallons (30 m3) per day. At a median concentration of 10,100 mg/L COD and a median pH of 4.9, efﬂuent concentrations for COD and BOD5 are 150 mg/L and 40 mg/L, respectively (Blumberg Engineering).
Secondary benefits Sustainable development often revolves around the provision of secondary beneﬁts. Designing for multiple uses frequently prevents the common problem of addressing and solving a single issue while simultaneously creating other problems.
Figure 6.6 This hybrid wetland in Hennersdorf, Germany, treats surface run-off from a livestock operation. The newly planted floating mats of emergent vegetation reduce nitrogen and BOD in the first treatment stage (sedimentation and buffer ponds). After the sedimentation pond and similar buffer pond, the water is treated in a vertical subsurface stage and a horizontal subsurface flow wetland. The use of vegetated floating mats is useful in stormwater ponds also. Photo: Blumberg Engineers, www.blumberg-engineers.com. License: reproduced with permission.
HYBRID CONSTRUCTED WETLANDS 95
The addition of a free water surface stage to a hybrid treatment wetland exponentially increases the secondary beneﬁts to the community or the ecosystem or both. The visual appeal of open water draws visitors, as it adds variety to the landscape. Water also attracts birds and other wildlife that are of interest to people. In the image of the central park and municipal wastewater treatment hybrid wetland shown in Figure 6.7, three wetland types are visible. At the upper left of the image, there are three vertical subsurface ﬂow panels that are the ﬁrst treatment stage. In the middle of the image, two panels of horizontal subsurface ﬂow wetlands are visible. Adjacent to these is a linear pool, and, at the bottom, the free water surface wetland completes the treatment sequence. Treated water is collected in a tank for non-potable reuse. A few of the other park amenities on this intensively developed 1.5-acre site are also visible in the image. This park is on the island of Koh Phi Phi near the coast of Thailand, where the tropical climate makes growing wetland plants with large colourful ﬂowers possible. Canna and Heliconia are planted in the vertical subsurface wetland, while Canna are planted in horizontal subsurface ﬂow wetlands. The hybrid wetland performed very well, but illegal sewer connections without septic tanks caused problems later (Brix, 2011). The design of the free water surface wetland beds in this project discourages contact with the water. If the water was more accessible, and if the vertical and horizontal subsurface stages did not result in water quality appropriate for secondary recreation, then a disinfection step would be required. Although multifunctional hybrid wetlands are not yet common, the park-like setting shown in Figure 6.8 is a second example of effective wastewater treatment, in this case for a restaurant and tourist centre on Lotus Island in Lake Yangcheng near Suzhou, China. Constructed in 2009, this wetland treats as much as 7,925 cubic feet (30 m3) of domestic sewage per day. Figure 6.8 shows two round plantings of Phragmites and Canna. These plant masses indicate vertical subsurface ﬂow wetlands (3,767 feet2, 350 m2) and the ﬁrst stage of treatment after the septic tank. The second stage is a 1,077 square feet (100 m2) horizontal subsurface ﬂow bed (Blumberg Engineers). Free water surface wetlands that are commonly used in the United States as a tertiary treatment stage after conventional wastewater treatment plants have demonstrated outstanding ecosystem values, especially when planted with a diversity of plant species, open water and marsh areas with varying water depth. Free water surface wetlands are commonly used in the United States as a tertiary treatment stage
Figure 6.7 Koh Phi Phi, Thailand, is a hybrid wetland for treatment of municipal wastewater but also as the central park for the community. Photo: Hans Brix, Aarhus University, Denmark. Reproduced with permission.
96 HYBRID CONSTRUCTED WETLANDS Figure 6.8 Aesthetics were important in this wetland constructed to treat of domestic sewage since it is at an ecotourism resort. Several similar small-scale projects along Lake Yangcheng protect the water quality of the lake and the tourism industry. Photo: Blumberg Engineers, www.blumberg-engineers.com. License: reproduced with permission.
Figure 6.9 The upper-right portion of this image shows the three vertical subsurface flow wetland stages of the Shengyang wetland. The rest of the wetland receives the treated wastewater and stormwater. Photo: Blumberg Engineers, www.blumberg-engineers.com. License: reproduced with permission.
HYBRID CONSTRUCTED WETLANDS 97 Figure 6.10 The treated effluent from the three vertical subsurface flow beds drains into the stormwater wetland. Photo: Blumberg Engineers, www.blumberg-engineers.com. License: reproduced with permission.
after conventional wastewater treatment plants. When located as a ﬁnal stage in a hybrid treatment sequence, free water surface treatment wetlands offer outstanding ecosystem beneﬁts. These are maximized when the free water surface cell is planted with a diversity of species and features open water and marsh areas with varying water depth. Figure 6.9 is an aerial image of the Shenyang (China) project discussed in the chapter on vertical subsurface ﬂow wetlands. It shows the three panels of the vertical ﬂow treatment wetlands in the upper right corner. Free water surface wetlands are at the left and bottom. They receive treated efﬂuent and untreated stormwater. The aesthetic and wildlife values are remarkable for this densely developing urban centre (Figure 6.10).
References Ávila, C., Bayona, J. M., Martín, I., Salas, J. J. and García, J. “Emerging organic contaminant removal in a full-scale hybrid constructed wetland system for wastewater treatment and reuse,” Ecological Engineering, vol 80, pp. 108–116, July 2014. Ávila, C., Salas, J. J., Martín, I., Aragón, C. and García, J. “Integrated treatment of combined sewer wastewater and stormwater in a hybrid constructed wetland system in southern Spain and its further reuse,” Ecological Engineering, vol. 50, pp. 13–20, January 2013. Blumberg Engineering, “Cascade of ponds and constructed wetlands for treatment of agricultural polluted surface run-off.” Blumberg Engineers, “Treatment wetlands at Lotus Island on Yangchen Lake, Suzhou, China.” Brix, H., Koottatep, T., Fryd, O. and Laugesen, C. H. “The ﬂower and the butterﬂy constructed wetland system at Koh Phi Phi – System design and lessons learned during implementation and operation,” Ecological Engineering, vol. 37, no. 5, pp. 729–735, 2011. Burka, U. “A new community approach to waste treatment with higher water plants,” in Constructed Wetlands in Water Pollution Control, Oxford: Pergamon Press, 1990. Gaboutloeloe, G. K., Chen, S., Barber, M. E. and Stöckle, C. O. “Combinations of horizontal and vertical ﬂow constructed wetlands to improve nitrogen removal,” Water Air Soil Pollution: Focus, vol. 9, no. 3–4, pp. 279–286, 2009. Vymazal J. and Kröpfelová, L. “A three-stage experimental constructed wetland for treatment of domestic sewage: First 2 years of operation,” Ecological Engineering, vol. 37, no. 1, pp. 90–98, 2011.
7 Plants in constructed wetlands Introduction Plants in the various types of wetlands and bio-retention basins have multifaceted roles. They have important engineering functions, but ecological contributions are a critical concern in sustainable development. There are also aesthetic, educational and even social dimensions to the plants that are selected (Figure 7.1). Finally, there are maintenance and even possible economic returns that should be considered. Since environmental engineers have conducted most of the research leading to the development of constructed wetlands, many of the roles that plants play have been poorly explored. Initial research on plants for constructed wetlands focused on the survivability and rooting depth of macrophytes planted in domestic wastewater. A few of the most common species have been investigated according to their capacity to absorb nitrogen, phosphorus, heavy metals and other substances into their roots, stems and leaves. Less research has been devoted to the ecological and aesthetic aspects of plants in constructed wetlands than their engineering properties. Since this book focuses on sustainability issues, plants are of interest for their full range of contributions. Since constructed wetlands are engineered systems, the technical performance of the plants must be balanced with the practical considerations of the effort and cost of installation and maintenance. The great difference between wastewater treatment wetlands that are continuously supplied with water and the intermittently supplied stormwater or agricultural treatment wetlands has an impact on the types of plants that can be speciﬁed. Similarly, differences in climate, particularly precipitation and cold, limit or expand the palette of plants available to the designer. From a sustainable development perspective, the opportunity is to increase the diversity of plants, especially native species that are speciﬁed and planted in constructed wetlands of various types. The challenge is to maintain or improve the engineering functions that the typical monoculture of plants contributes, while adding ecosystem, aesthetic and other beneﬁts. This chapter will address the selection of plants to achieve greater diversity, while managing the more complex installation and maintenance issues that diversity might pose. The following section addresses the physical and cultural characteristics of the most commonly speciﬁed plants for constructed wetlands around the world, but a section that proposes associations of plants to create additional ecosystem service beneﬁts and ecosystem functions follows it.
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Commonly selected plants Although approximately 150 species have been planted in constructed wetlands, by far the most frequently planted species are Typha latifolia, cattail (common in North America); Phragmites australis, common reed (very common in Europe and Asia); Typha angustifolia, narrowleaf cattail; Juncus effusus, common or soft rush; Scirpus (Schoenoplectus) lacustris, bulrush; Scirpus californicus and Phalaris arundinacea, reed canary grass. Another common genus is Eleocharis, spikerush. While Phragmites australis and Typha domingensis, southern cattail, predominate in the Central and South Americas, and Scirpus validus (S. tabernaemontani), soft-stem bulrush, occurs broadly in Australia and the islands of the south and central Paciﬁc Ocean. Cyperus papyrus is commonly used in Africa (Vymazal, 2013). Most engineered constructed wetlands are planted with a single species that is selected because it is native, has long roots, spreads assertively and is characterized by high biomass production. However, a few constructed wetlands have been studied that are planted with a variety of species. The Houtan Park wetland shown in Figure 7.2 is an exception that features an expansive plant palette. Multi-species wetlands seem to perform as well or better in their treatment function, ecological and
Figure 7.1 The planting design for constructed wetlands should match the species to the hydrology, as in this free water surface stormwater wetland in Tianjin, China, designed by Turenscape. The plants occur in zones that respond to seasonal soil moisture and the depth and duration of inundation. Photo: Kongjian Yu, 2014.
Figure 7.2 This free water surface wetland treats polluted river water and stormwater, but the consistent water level creates niches for various species of plants and aquatic organisms. Photo: Gary Austin, 2015.
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aesthetic roles (Tanner, 1996). A mixed community horizontal subsurface ﬂow wetland in subtropical China was planted with 20 plants each of Canna indica, Cyperus ﬂabelliformis, Phragmites australis, Pennisetum purpureum and Hymenocallis littoralis. These species were equally spaced and randomly distributed. At the end of the 4-year study, the Phragmites (common reed) had expanded at the expense of all other species (the Pennisetum disappeared from the plots altogether). Nevertheless, the mixed community plots generally showed better performance than the monoculture wetlands after the ﬁrst year (Liang et al., 2011). A study in the Czech Republic also demonstrated that sometimes Phragmites completely replaced Phalaris arundinacea after several years, but in other instances Phalaris (reed canary grass) maintained its extent (Brˇezinová and Vymazal, 2014; Vymazal and Kröpfelová, 2005). A study of ﬁve subtropical plants (Acorus calamus, Canna indica, Cyperus ﬂabelliformis, Phragmites australis and Hymenocallis littoralis) growing in mixed beds in constructed wetlands demonstrated that the mixed plantings treated the wastewater as well as single specie beds. However, Canna indica, Cyperus involucratus and Phragmites australis were more aggressive competitors for light and space than Acorus calamus and Hymenocallis littoralis (Qiu et al., 2011). Similarly, Typha latifolia often replaces Scirpus cyperinus and Juncus effusus when they are planted together. A review of several studies of mixed vegetation highlights the problem of species competition and change over time. If, for treatment, ecological or aesthetic reasons, a community of plants is desired, then careful attention to plant selection (and avoidance of aggressive non-native species) and other measures will be required to meet the design goal. Changing the installation method and initial maintenance to favour mixed communities requires additional study. However, rather than mixing the species randomly, patches of single species and staged planting times may yield more stable mixed-species constructed wetlands. Similarly, providing root barriers between plants
Figure 7.3 Aggressive species can expand to dominate the plant community. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
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that spread aggressively via rhizomes or stolons will reduce maintenance and preserve the distribution of plants. These techniques were successfully employed at Houtan Park in Shanghai, China, where the landscape architect speciﬁed a highly diverse palette (see Chapter 8 on ‘riparian wetlands’). The expanded palette was possible in part by the highly variable wetland conditions that ranged from deep to shallow water, oxygen abundant and oxygen depleted and other variations (Figure 7.4). Of course, we need not limit our planting proposals to the area of the constructed wetland. The margins and even upland zones can be fashioned to provide differing cultural conditions that favour species not normally associated with constructed wetlands, such as low growing sedges that require a dry season or plants intolerant of more than a few inches of inundation (Figure 7.1). In summary, there are abundant opportunities to expand the diversity, aesthetic impact and ecosystem beneﬁt of the plant palette through creative and knowledgeable selection of plants and organization of cultural conditions needed to allow them to thrive. The sections below describe the cultural, aesthetic, ecosystem and treatment capabilities of some of the plants that are commonly used in constructed wetlands. It also features a number of plants that are less commonly used but which show promise according to initial research. The plants have been divided into groups according to their ecological adaptation to inundation. The groups are emergent, submerged and ﬂoating. The cultural requirements of wetland plants include tolerance for permanent and temporary inundation depth. Therefore, species can be grouped according to their position on a gradient from upland to deep water (Figure 7.5).
Figure 7.4 Carefully controlled water depth, staged planting and good maintenance during the first year resulted in plant diversity and good aesthetic quality at Houtan Park, Shanghai. Photo: Gary Austin, 2015.
Figure 7.5 This image shows a full range of wetland plants. On the left, submerged plants colonize much of the open water channel, while the right side of the stream features floating leaved plants and then emergent vegetation in the shallow water. Photo: Gary Austin, 2015.
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Emergent vegetation This type of macrophyte is the primary kind of vegetation in all constructed wetland types with the exception of those depending on free ﬂoating plants. The species listed below may perform somewhat differently in treatment wetlands depending whether oxygen is abundant (as in vertical subsurface ﬂow wetlands) or limited (as in horizontal subsurface ﬂow wetlands). In free water surface wetlands treating stormwater, the length of the dry season, the depth to groundwater, and the depth and duration of inundation deﬁne cultural niches for the plants. In subsurface ﬂow wetlands, the high strength municipal or industrial wastewater is better tolerated by some species than others. In free water surface wetlands, plants are often grouped according to the normal water depth (Figure 7.6), although the depths assigned for each zone vary somewhat. Common deep marsh species that grow vigorously in water 12–30 inches deep (30–76 cm) include Phragmites australis, P. karka, Eleocharis dulcis, Typha latifolia T. angustifolia, Scirpus californicus, S. grossus, S. mucronatus, Lepironia articulate and Phylidrium lanuginosum (Sim, 2003). Common marsh species that grow vigorously in water 6–16 inches deep (15–41 cm) include Thalia geniculate, Rhynchospora corymbosa, Eleocharis variegate, Scleria sumatrana, Fimbristylis globulosa, Polygonum barbatum and Erioucaulon longifolium (Sim, 2003). In a stormwater wetland, a normal water level of 12 inches for the shallow marsh should be designed to ﬂuctuate no more than 6 inches above and below this level. The shallowest water (2–6 inches; 5–15 cm) is the zone for wet meadow species, such as Iris pseudacorus and some Carex. For bio-retention and stormwater basins or other situations where water ﬂuctuates seasonally, species adapted to an extended dry season should be speciﬁed. Some rushes (Juncus), spikesedges (Eleocharis) and sedges (Carex) tolerate this alternation of inundation and dry land conditions. For stormwater wetlands, the normal water level must be well controlled to sustain the intended vegetation. Stormwater wetland zones include deep-water marsh, marsh, shallow marsh 2–8 inches (5–18 cm) and ephemeral marsh 0–2 inches (0–5 cm) (dries out) (Greenway, 2012). The expectation is that the water depth varies seasonally but
Figure 7.6 In natural wetlands, water levels fluctuate and create niches for rooted, submerged and floating wetland plants. In constructed wetlands, the plant zones can be created as benches. A – Upland terrestrial plants; B – Wet meadow, 2–6 inches water depth with facultative plants; C – Shallow marsh, 6–16 inches water depth, with emergent plants and aquatic creepers; D – Deep marsh, 30–36 inches water depth with emergent and floating-leaved rooted plants; E – Open water, more than 36 inches water depth with submerged and free floating plants. Image: Gary Austin adapted from Greenway (Greenway, 2012).
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that the depth of inundation over the levels listed above are reduced within days through the use of outlet structures, inﬁltration rates or evapotranspiration. Furthermore, the water depth immediately after planting must be regulated to allow about one-third of the plant’s foliage to be above the water level during a 6–8-week plant establishment period. Poor regulation of the water depth or excessive duration of inundation causes planting designs to fail. Figure 7.7 illustrates a portion of a planting design that was implemented at a stormwater wetland in Australia. The plants were distributed based on water depth in several zones: ephemeral marsh, 14 per cent; shallow marsh, 23 per cent; marsh, 24 per cent; deep marsh, 20 per cent; open water, 19 per cent. However, after 6 months, the plants, particularly in the marsh and deep marsh areas, were largely replaced by open water. This was due to poor design of the outlet structure and the presence of short circuit ﬂows. The more direct ﬂow of water through the wetland during storm events scoured the soil and uprooted the plants. The outlet established deeper inundation for longer periods than the plants could survive. Unrelated but also signiﬁcant was the uprooting of facultative plants by maintenance workers without the knowledge to distinguish the wetland plants from weeds. To better preserve the plants and the treatment capacity of the stormwater wetland, a maximum inundation depth of 12 inches above the normal water level is recommended. The water level should return to the elevation of the normal pool within 48 hours. These general recommendations should be modiﬁed depending on local conditions (rainfall intensity, rainfall frequency) and the plants speciﬁed. The velocity of ﬂow of stormwater through a wetland can damage plants with soft foliage, and some are even uprooted as stormwater carries soil away from the root zone (Greenway, 2012). In general, designing the treatment wetlands to receive only a water quality storm while an adjacent pool contains and transmits larger, less frequent storms will yield a better treatment and planting result than a single basin that detains large storm events, such
Figure 7.7 The depth and duration of inundation must be managed to sustain the planting design and treatment performance of stormwater wetlands. This plan represents the installed planting design establishing the following zones: A – Boardwalk; B – Ephemeral marsh, 14 per cent; C – Shallow marsh, 23 per cent; D – Marsh, 24 per cent; E – Deep marsh, 20 per cent; F – Open water, 19 per cent. However, the open water zone was greatly enlarged at the expense of the deep marsh and marsh zones due to hydraulic problems. Image: Gary Austin adapted from Greenway (Greenway, 2012).
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as the 25-year storm. See Chapter 9 on ‘stormwater’ for more details about on-line and off-line stormwater wetlands. In general, it is best to specify native species of plants. For large projects, it is possible to contract nurseries to grow local wetland plants. This often requires collection and propagation of seed, so it takes several months to get plants ready after completing the wetland construction. A botanist might be necessary to identify local species. However, the landscape architect might be able to do this with the support of local nurserymen and other resources, such as a species list like those published by the US Army Corps of Engineers for every state and territory in the United States (http://rsgisias.crrel.usace.army.mil/NWPL/). The text below provides the cultural requirements of many emergent wetland plants and also identiﬁes which plants demonstrate accumulation of nutrients, heavy metals and other contaminants. Similarly, it identiﬁes plants with outstanding visual characteristics and suitability for tropical, subtropical and temperate climates.
Typha latifolia The common or broad-leaved cattail is a widely distributed North American native plant that grows 5 to 10 feet tall (1.5–3 m) and in water 2.6 feet deep (0.8 m) or less (Figure 7.8). Typha angustifolia (Figure 7.9), native to Europe and northern Asia, is capable of growth in deeper water than T. latifolia. Along a water depth gradient, broadleaf cattail often grows upslope from bulrush or open water but downslope from
Figure 7.8 Broadleaf cattail, Typha latifolia, is an attractive and vigorous wetland plant.
Figure 7.9 Typha angustifolia has slender seed heads and leaves ( 1⁄4–1⁄2 inch wide). It grows 3–6 feet tall.
Photo: Gary Austin, 2015.
Photo: Don Pedro28. License: CC-BY-SA-3.0.
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common reed (Phragmites australis), reed canary grass (Phalaris arundinacea) and willow (Salix spp.). Cattail often forms extensive patches but also grows in mixed stands with bulrush and other species. Typha stands expand rapidly when there are changes in nutrients, salinity and hydrology. In this case, they can replace other native species. T. latifolia is reported to overwhelm Scirpus cyperius and Juncus effuses in a mixed planting (Calheiros et al., 2009). To reduce an invasive stand as part of a restoration plan, mowing cattails after the seed heads are well formed but not mature and again a month later, when new growth is 2 or 3 feet high, will kill at least 75 per cent of the plants (Stevens and Hoag, 2006). The best survival of new plants occurs when dormant rhizomes are planted in October or November in moist soil after frequent rainstorms. Rhizomes should be planted about 3 feet apart, except in clay soils where smaller spacing is necessary. Seed germination is high and growth from seed is effective when established in aerobic, rather than ﬂooded, soil (Stevens and Hoag, 2006). Typha is quite effective for the treatment of sewage and other efﬂuents high in organic nitrogen. For example, Typha was able to treat tannery wastewater with high biological oxygen demand (BOD; 420–1,000 mg/L) and chemical oxygen demand (COD; 808–2,449 mg/L) concentrations (Calheiros et al., 2009). The species is also able to accumulate nitrate and ammonium. Although most wetland plants contain about the same amount of nitrogen in their aboveground stems and leaves, for cattail, this is lower than in other common species at 0.8 per cent of the dry matter. Cattail allocates more of its nitrogen to the rhizomes. The rhizomes are about 1 inch thick and often over 24 inches long. Because the plant is quite vigorous, it produces a great amount of biomass. Combined, these characteristics result in a substantial accumulation of nitrogen. According to one study, about 22 g/m2 of nitrogen is harvested annually from the aboveground portions of the plant when the nitrate and ammonium concentrations in the water are low (86 g/m2) and 107 g/m2 when the nitrogen concentration is moderate (222 g/m2). These concentrations are similar to those in stormwater and agricultural run-off, but lower than for domestic wastewater. The belowground portions of the plants account for an additional 103 g/m2 of nitrogen (Borin and Salvato, 2012). One study found that T. latifolia was stressed by ammonia concentrations averaging 160–170 mg/L (Wu et al., 2015). A study of three free water surface constructed wetlands in Spain found that Typha latifolia generally removed greater amounts of nitrate and ammonium than Phragmites australis. These wetlands treated secondary efﬂuent from a wastewater treatment plant. However, the distribution pattern and amount of coverage of the treatment cells by emergent vegetation had a great effect on total nitrogen removal (and hydraulic residence time) (García-Lledó et al., 2011). T. latifolia demonstrated the capacity to grow in acidic (3.9–4.3 pH) leachate with average COD of 3,980 mg/L and BOD of 3,565 mg/L from wood waste piles at a sawmill. These free water surface constructed wetlands were 16 inches deep with a 7-day residency time (Masbough et al., 2005). T. latifolia can also tolerate total dissolved solids (primarily calcium, phosphates, nitrates, sodium, potassium and chloride) concentrations as high as 2,500 mg/L and long-term exposure to copper at 30 mg/L (Valipour et al., 2014). Cattails provide cover and nesting sites for long-billed marsh wrens, red-wing blackbirds and yellow-headed blackbirds, but are food for few birds, although geese
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eat new shoots and a few duck species consume the seeds. The roots are valuable for muskrat, while moose and elk eat the spring shoots (Stevens and Hoag, 2006). Typha domingensis and T. orientalis are very similar species also planted in wastewater treatment wetlands in Australia and elsewhere.
Phragmites spp. There are several species of common reed, including Phragmites karka (India, Nepal), Phragmites japonica (Japan) and Phragmites mauritianus (central Africa); however Phragmites australis (Figure 7.10) has a nearly global distribution, although it is most common in Europe and Asia. The attractive plants (Figure 7.11) grow between about 3 feet wide and 15 feet high, and spread primarily via rhizomes rather than seed. The tall plant grows in dense stands and is anchored by deeply penetrating roots (0.6–1.0 m). The stiff stems are hollow between several nodes (Vymazal, 2013). P. australis is the most commonly speciﬁed plant for both subsurface ﬂow and free water surface constructed wetlands. Therefore, it has been studied extensively for its capacity to grow in water with a range of nutrient loads and toxic contaminants. Phragmites tolerates domestic and municipal wastewater that has been simply screened or pretreated in a septic tank or similar device. It also tolerates industrial wastewater (Xu et al., 2010). For example, it is used to treat wastewater from tanneries, pulp and paper mills, and animal wastewater from dairies and piggeries. It grows successfully in tannery wastewater with BOD concentrations of 420–1,000 mg/L and COD concentrations of 808–2,449 mg/L (Calheiros et al., 2009). Because it is proliﬁc and invasive, Phragmites is avoided in parts of the United States and New Zealand. It can grow in water with salinity as much as 20 parts per thousand, making it useful for treatment of brackish water or wastewater that has high salinity due to high evaporation rates, as in arid areas (Vymazal, 2013).
Figure 7.10 Phragmites australis often grows in dense stands. In China’s Liaohe Delta, about 197,700 acres (800 km2) of natural wetland is managed for maximum production of Phragmites biomass. Harvested each winter, this wetland produces nearly 440,925 tons (400,000 metric tons) of biomass that is used to make paper. Unfortunately, this commercial enterprise sometimes includes the use of pesticides and burning to maximize yields, resulting in ecosystem shocks (Brix et al., 2014). Photo: Botaurus Stellaris. License: public domain.
PLANTS IN CONSTRUCTED WETLANDS 107 Figure 7.11 Phragmites australis features attractive seed plumes that persist through the winter. Photo: Peter aka anemoneprojectors License: CC-SA-2.0.
Phragmites australis, due to its high biomass and density, has the capacity to accumulate 2.5 kg of nitrogen per hectare and 120 grams of phosphorus per hectare per year. These are more than twice the amount accumulated by Cyperus papyrus (1.1 kg N hectare per year and 50 g P hectare per year) in the same setting (Brix, 1994). Like Typha, Phragmites produces a great deal of biomass and accumulates nitrates and ammonium. Where there is an input of 222 g/m2 of nitrogen in the form of nitrate and ammonium, Phragmites accumulates 63 and 83 g/m2 of nitrogen in its above and belowground portions, respectively. This is somewhat less than that reported for Typha latifolia (Borin and Salvato, 2012). Whether growing in diluted or full strength domestic wastewater, Phragmites acquires the same amount of nitrogen. When growing in the presence of 179 M of ammonium (NH4), this species shows no reduction in growth rate and biomass production was not reduced at 3,700 M NH4, whereas these levels were limiting to another common wetland plant, Glyceria maxima (Reed mannagrass) (Tylová et al., 2008). Phragmites effectively accumulates heavy metals present in mixed residential and industrial efﬂuents. This species performed better than Typha latifolia for the removal of most metals, although a mixed planting of the two species appears to be most effective for the removal of copper (78.0 per cent), cadmium (60.0 per cent), chromium (68.1 per cent), nickel (73.8 per cent), iron (80.1 per cent), lead (61.0 per cent) and zinc (61.0 per cent) when a 14-day water residence time is provided (Kumari and Tripathi, 2015). The capacity to accumulate copper, zinc, cadmium and nickel was also evident from an Italian study, where river water was treated in a free water surface constructed wetland (Bragato et al., 2009). In its native range, P. australis is subject to damage by the larva of a stem-boring moth (Archanara geminipuncta), which kills or damages shoots. Although the general impact on the plant is negative, this insect also encourages a growth response and fosters greater biological diversity (Tscharntke, 1999) (Figure 7.12). There is a North American Phragmites named P. australis subspecies americanus (Figure 7.13) with equal nitrogen removal characteristics and perhaps greater
108 PLANTS IN CONSTRUCTED WETLANDS Figure 7.12 In its native range, Phragmites australis hosts a diversity of insects that attract other species to the wetland. Photo: Sebastien Bertru. License: CC-BY-SA-2.0.
Figure 7.13 Phragmites australis often forms dense single species stands. Photo: USFS. License: CC-BY-SA-2.0.
phosphorus removal capacity. This subspecies should be speciﬁed for constructed wetlands in the United States and Canada to avoid the invasive nature of P. australis and to create a more authentic plant community (Rodríguez and Brisson, 2015). The American subspecies may have been introduced from Europe in the 1700s.
Juncus spp. Several Juncus species are grown in treatment wetlands including J. effuses (Figure 7.14), J. conglomeratus, J. articulatus, J. balticus, J. ﬁlliformis, J. ingens, J. kraussii, J. roemerianus and J. usitatus. They are most commonly speciﬁed in Europe and especially North America.
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Juncus (rush) species are leaﬂess, grass-like annual or perennial herbs with rhizomes. The species vary in height from less than 1 feet to 41⁄2 feet (25 cm–1.5 m). Juncus species are quite adaptable, tolerating periods of drought and total inundation. Stands of rushes provide habitat for amphibians, spawning areas for ﬁsh and wading birds ﬁnd shelter within the dense vegetation. Muskrats feed on the roots while waterfowl, songbirds and small mammals, such as jackrabbits, cottontail, muskrat, porcupine and gophers, eat rush seeds. Juncus species are rarely damaged signiﬁcantly by insect or diseases problems (Stevens, 2003). Juncus effusus (L.), soft rush, is the most commonly speciﬁed rush species for constructed wetlands in Europe and in North America (Vymazal, 2013). It occurs in wet places below 2,500 m and is distributed throughout California to British Columbia, the eastern United States, Mexico and Eurasia. The sturdy but soft stems stand erect and reach 2–5 feet (0.4–1.5 m) in height (Figure 7.15). While it grows in clumps, a mass of the plants exhibits a grass-like appearance due to the green stems, but brownish, leaf-like sheaths that are present at the base of the plant (Stevens, 2003). Soft rush is easy to propagate from the division of rhizomes or seed. Planting rhizomes or seedlings 10–12 inches (25–30 cm) apart encourages full coverage within a single growing season. Planting should occur in fall at the beginning of the rainy season in aerobic rather than ﬂooded soil. Seed can be collected in August and seed germinates in the greenhouse (32–38°C) in about a week. The plants can be installed in the ﬁeld within about 3 months, but older, larger plants have better survival. Established plants are vigorous and can become invasive (Stevens, 2003).
Figure 7.15 The Juncus effusus inflorescence appears to emerge from the side of the stem. Photo: Pethan Houten. License: CC-BY-SA-3.0.
Figure 7.14 Juncus effusus. Photo: Christian Fischer. License: CC-BY-SA-3.0.
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In natural wetlands and free water surface constructed wetlands, muskrats will use Juncus and other species for food and hut construction materials. The animals typically forage and clear an area around their huts. These open water areas increase the ecological diversity of the wetland (Stevens, 2003). Juncus effusus accumulates signiﬁcant amounts of arsenic within its rhizomes but not within its stems when exposed to contaminated water (simulated secondary wastewater efﬂuent) in a subsurface ﬂow tank, according to a laboratory study (Rahman et al., 2014). Similarly, when J. effusus plants are suspended from ﬂoating rafts in stormwater treatment ponds, the stems and roots accumulate nickel and zinc. However, the roots accumulated 5.7 and 2.6 times more nickel and zinc, respectively, than the stems (Ladislas et al., 2014). Other Juncus species such as Juncus articulatus, jointleaf rush, in Asia, Juncus conglomeratus (this is a variety of J. effusus) in Europe, or Juncus kraussii in Oceania have been used only occasionally in constructed wetlands (Vymazal, 2013).
Eleocharis spp. The genus Eleocharis (spikesedge) contains more than 250 species broadly distributed across the globe (Figure 7.17). Those reported for use in constructed wetlands are E. acuta, E. dulcis, E. fallax, E. obtusa, E. palustris (Figure 7.18), E. quadrangulata (Figure 7.16) and E. sphacelata (Figure 7.19). The use of these species is most common in Asia and especially in North America.
Figure 7.16 Squareside spikerush, Eleocharis quadrangulata, is native to Mexico and the United States. Photo: Mike Ryon. License: government work product.
PLANTS IN CONSTRUCTED WETLANDS 111 Figure 7.17 Eleocharis acicularis, needle spikerush, has a global distribution. Photo: Mike Ryon. License: government work product.
Figure 7.18 Eleocharis palustris, common spikerush, grows in USDA hardiness zones 4–8. Photo: Karelj. License: CC-BY-SA-3.0.
The species range widely in height to about 10 feet tall for Eleocharis sphacelata (Australia and New Zealand, Figure 7.19) and form patches or mats that are extended by rhizomes or stolons (Vymazal, 2013). The stems are photosynthesizing while the leaves are inconspicuously located at the base of the plant. The ﬂowers are simple and inconspicuous. Four species are common to constructed wetlands in North America. Eleocharis palustris, Common spikerush (Figure 7.18), is a widely distributed perennial in the United States that grows to 4 feet tall and is characterized by a dense root mat that extends more than 16 inches deep (40 cm). It can grow in water up to 3 feet deep for 3–4 months. It can also grow in drier soil where groundwater is available within 30 inches during the dry season (Ogle, Tilley and John, 2012).
112 PLANTS IN CONSTRUCTED WETLANDS Figure 7.19 Eleocharis sphacelata, tall spikerush, grows in USDA zone 8, tolerating temperatures from 10 °F to 20 °F (–12 °C to –6.5 °C). Photo: John Tann. License: CC-BY-2.0.
Figure 7.19 illustrates tall spikerush, Eleocharis sphacelata. It is frequently planted in constructed wetlands in Australia and New Zealand where it is native. This is a perennial species with sturdy rhizomes and stems. It is unusual in its ability to grow in deep water (up to 6 feet, 2 m). Eleocharis fallax (creeping spikesedge) is native to southern and eastern United States; Eleocharis obtusa, blunt spikerush, generally is 1 feet tall, while Eleocharis quadrangulata (Figure 7.16), squarestem spikerush, grows 1–3 feet tall. Eleocharis dulcis (Chinese water chestnut), a freshwater rhizomatous perennial emergent macrophyte (Figure 7.20), is most common in free water surface constructed wetlands in Asia and Oceania. Stems of this species are hollow, have an average diameter of 5 mm and grow to 6 feet tall (2 m) (Vymazal, 2013).
Phalaris arundinacea Phalaris arundinacea, reed canary grass (Figure 7.21), is distributed widely across the globe. It is cold hardy to –35°F (USDA zone 4) (Stannard and Crowder, 2002). This plant grows 2–9 feet tall (0.6–2.7 m) and has a medium texture with leaves 3.5–10 inches long (9–25 cm) (Figure 7.22). It sprouts early in the spring and forms a dense root and rhizome network that dominates the soil mass (Stannard and Crowder, 2002). In constructed wetlands, the roots grow 8–16 inches long (20–40 cm) (Vymazal and Kröpfelová, 2005). This plant displaces other plants that sprout later or are deprived of light by the tall dense vegetation. In some temperate climate horizontal subsurface ﬂow wetlands, Phragmites encroaches on Phalaris, replacing it after several years but in other instances this has not been observed (Brˇezinová and Vymazal, 2014; Vymazal and Kröpfelová, 2005). This grass produces as much as 9 tons per acre (920 pounds of nitrogen per N acre) of biomass (but less biomass than Phragmites). In fact, it is sometimes cultivated as a biofuel feedstock in Scandinavia and as a reliable forage crop on poorly drained soils. Reed canary grass expands rapidly via new shoots along its rhizomes, but the stems are also capable of forming roots. Reed canary grass also grows from seed (it produces 30–50 pounds of seed per acre). Moderate germination rates occur after a
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Figure 7.20 Chinese water chestnut, Eleocharis dulcis, grows in USDA zones 9–11, tolerating temperature to 25 °F (–3.9 °C).
Figure 7.21 Phalaris arundinacea. Photo: Michael Becker. License: CC-BY-SA-3.0.
Photo: Robyn Jay. License: CC-BY-SA2.0.
Figure 7.22 Phalaris arundinacea is also sold as an ornamental plant as hybrids with variegated foliage or other characteristics. Photo: Patrick Standish. License: CC-BY-SA-2.0.
few days of cool temperatures. Seedlings are sensitive to competition, especially when the soil is dry. When established, the plant survives as much as 9 months of continuous grazing and responds well to as little as a 2-week grazing hiatus. Spring ﬂooding is well tolerated, as is burning. Reed canary grass is often planted in constructed wetlands or used as the target for irrigation disposal of municipal and industrial wastewater (Stannard and Crowder,
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2002). In the Paciﬁc Northwest region of the United States, the plant is aggressive and invasive, causing problems for riparian restoration as it displaces native species. Prolonged deep inundation can be used to control the growth of P. arundinacea. Phalaris biomass can be reduced by nearly 70 per cent through shading from the planting of willows (Scouler willows, Salix scouleriana, and Paciﬁc willows, Salix lasiandra) at 2 feet (0.6 m) apart in moist soils. This is less effective where the willows and reed canary grass are exposed to drought stress (Kim, Ewing and Giblin, 2006). Phalaris accumulates metals in its stems and leaves when growing in municipal wastewater. In a temperate climate, harvesting the aboveground biomass in May or June is optimum for removal of zinc, copper and nickel. Harvest in September is better for the removal of chromium, in July for removal of cadmium, and in August for removal of lead (Brˇezinová and Vymazal, 2015). However, this plant is not particularly tolerant of high concentrations of zinc compared to Phragmites australis, Typha latifolia, Glyceria ﬂuitans, Eriophorum angustifolium, Festuca rubra and Carex rostrata (Matthews, Moran and Otte, 2006).
Scirpus (Schoenoplectus) spp. Bulrushes, Scirpus, are annual and perennial herbaceous plants that grow to 10 feet tall (3 m) in some species. Root penetration is 27–31 inches deep (70–80 cm). The plants lack leaves and the stems range from sharply to softly triangular in cross section (Vymazal, 2013). In Germany, Dr Kathe Seidel planted Scirpus lacustris (Common clubrush) in her early wastewater treatment experiments. This species is planted in Europe, while other species are commonly part of constructed wetlands in North America, including Scirpus acutus (Hardstem bulrush), S. americanus (Chairmaker’s bulrush), S. californicus (Giant bulrush) and S. cyperinus (Woolgrass) (Vymazal, 2013). Scirpus californicus (Figure 7.23) is native to temperate South America, the southern United States, California and Oregon where it is an important species for marsh and shore birds. Marshes in California dominated by S. californicus are the primary habitat for the endangered Santa Cruz long-toed salamander and the rare giant garter snake. Seedlings should be planted 3 feet apart in aerobic, not ﬂooded,
Figure 7.23 This image of Scirpus californicus illustrates the inundation tolerated by this 5–8 feet tall macrophyte. It grows in USDA hardiness zone 8, tolerating temperatures of 10 ° to 20 °F (–12.5 ° to 6.7 °C). Photo: US National Park Service, Santa Monica Recreation Area. License: government work product.
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soil. In a constructed wetland, S. californicus provides good removal of aluminium, copper, iron, lead, manganese, zinc and total petroleum hydrocarbons. River clubrush, Scirpus validus (Schoenoplectus tabernaemontani), is the primary bulrush species planted in constructed wetlands in Australia and New Zealand (Vymazal, 2013), but is distributed throughout the United States and much of Canada. It grows naturally in fresh and brackish water, along creeks, lakes and marshes, but grows best in saline conditions. Planting 3 feet apart yields complete coverage within one growing season. S. validus grows very rapidly in primary wastewater from dairies, yielding an aboveground biomass of 2 kg/m2 of dry weight and a belowground biomass weight of 1.25 kg/m2 in a horizontal subsurface ﬂow constructed wetland (Tanner, 1994). Some studies report a shallow root depth (10–30 cm) for S. validus, which grows in small groups or large colonies (Figure 7.24). One microcosm study of S. validus revealed that the plant preferentially acquired ammonium when both ammonium and nitrate were available. This suggests that it is well adapted for growth in horizontal subsurface ﬂow wetlands, where ammonium is generally more abundant than nitrate. S. validus absorbed more ammonium than Canna indica under the same conditions (growing in simulated secondary efﬂuent). Similarly, S. validus absorbed slightly more phosphorus (PO4) than Canna (Zhang, Rengel and Meney, 2009). S. validus also demonstrates the ability to tolerate high levels of ammonia (160–170 mg/L) (Wu et al., 2015), although a second study showed biomass reduction when ammonia was in excess of 100 mg/L (Clarke and Baldwin, 2002). Another study noted root death when ammonia concentrations reached an average of 222 g/m3 (Tanner, 1994). The highest accumulation of total nitrogen seems to require a 7-day water residence time in a horizontal subsurface ﬂow wetland treating primary dairy inﬂuent. At this residence time, total nitrogen and total phosphorus reduction in mass reached as much as 75 per cent and 74 per cent, respectively (Tanner, Clayton and Upsdell, 1995). Scirpus maritimus (Bolboschoenus maritimus) is distributed widely around the world and valuable due to its tolerance to alkalinity and salt (Figure 7.25). It is often
Figure 7.24 River clubrush, Scirpus validus, grows in USDA zones 3a to 9b, tolerating temperatures as low as –40 °F. Photo: Matt Lavin. License: CC-BY-SA-2.0.
116 PLANTS IN CONSTRUCTED WETLANDS Figure 7.25 Scirpus maritimus grows in USDA zone 4 and warmer tolerating temperatures of –30 ° to –20 °F (–34.4 ° to –28.9 °C). Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
a pioneer species that grows to 4.5 feet tall and tolerates constant water depths of 12 inches and inundation to 3 feet (Tilley, 2012). It naturally colonized portions of the large constructed wetland near the Venice Lagoon (Italy) where Phragmites had been planted. While it grew vigorously there, it accumulated less nutrients and heavy metals (with the exception of sodium) than common reed (Bragato, Brix and Malagoli, 2006).
Carex There are a couple of thousand species in this genus, which occur across most of the globe. Most of these are native to wet environments of various types. With so many native species to choose from, avoiding the use of invasive Carex species is clearly possible by collecting plants or purchasing them from regional nurseries. Many species of Carex are planted in constructed wetlands including C. apressa, C. aquatilis, C. cristella, C. elata, C. frankii, C. lacustris, C. lurida, C. nebrascensis (Figure 7.27), C. normalis, C. obnupta, C. rhynchophis, C. riparia, C. rostrata and C. stipata (Figure 7.28). The most commonly planted of these is C. riparia (Figure 7.26). This species is native to Europe where it is widespread occurring as far south as North Africa and east to China. It is naturalized in New Zealand and occurs in South America. It grows to 3–4.5 feet (1–1.5 m) and can grow in water as much as 18 inches deep. Carex nebrascensis, Nebraska sedge, is an example of a North American plant that is widely distributed through the Midwest, west and southwest United States, and central Canada. It grows about 3 feet tall and has inch-wide grass-like leaves. C. nebrascensis tolerates total inundation for as long as 3 months.
PLANTS IN CONSTRUCTED WETLANDS 117 Figure 7.26 Carex riparia, grows 4 feet (130 cm) and is hardy in USDA hardiness zones 5–9. Photo: Karelj. License: Public Domain.
Figure 7.27 Carex nebrascensis, Nebraska Sedge grows in USDA zones 4–8. Photo: Andrey Zharkikh. License: CC-BY-2.0.
Figure 7.28 Carex stipata (Awl-fruit sedge) is distributed throughout Canada and almost all of the United States. It grows to 36 inches tall and tolerates shade. It grows in USDA zones 3–9. Photo: Matt Lavin. License: CC-SA-2.0.
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In its natural setting, this species sometimes forms dense stands, but generally it is the dominant plant associated with water sedge (C. aquatilis), common spikerush (Eleocharis palustris), cattail (Typha spp.), bulrush (Scirpus spp.) and other wetland plants. C. nebrascensis forms a dense mat of roots and rhizomes making it useful for erosion control and wastewater treatment. The plant requires a season where the soil dries somewhat, making it valuable for stormwater basins. It should be planted from seedlings 6 or 24 inches apart for complete coverage in 1 or 3 years, respectively. Planted seedlings require water depth of 1–2 inches until they are about 12 inches tall. C. nebrascensis can be propagated from seed in a greenhouse (Boonsaner, Borrirukwisitsak and Boonsaner, 2011; Calheiros, Rangel and Castro, 2009). Carex aquatilis, water sedge, is distributed throughout Canada and all but the southeast quadrant of the United States, although it is threatened or endangered in Connecticut, New Jersey and Pennsylvania. The plant grows where the water table is high in bogs, stream and lake margins and wet meadows in monoculture stands or mixed with other sedges, rushes and bulrushes, willow, birch and cottonwood. It can withstand as much as two months of inundation, but normally grows in only a few inches of water. C. aquatilis grows 6–40 inches (15–100 cm) tall and at temperatures as low as –4°F (–20°C) (Tilley, 2011). Water sedge is eaten by bison, caribou, mule deer, white-tailed deer and elk as well as by geese, swans and other waterfowl. The vegetation also provides a source of cover for birds and, as C. Aquatilis sod overhangs streams, it provides cover for ﬁsh. The sod is also an erosion protection. Propagation is by division of rhizomes but grows readily from seed in a greenhouse. Seedlings should be planted 6 inches apart (15 cm) for full coverage in 1 year (Tilley, 2011).
Iris Iris pseudacorus is native to Europe, western Asia and northwest Africa, and is one of the best choices for treatment of domestic sewage in constructed wetlands. It grows 39–59 inches (100–150 cm) tall with erect leaves 35 inches tall (90 cm) and 1.2 inches wide (3 cm). This species can be invasive and difﬁcult to eradicate outside of its native range. In the United States, its use is restricted in Connecticut, Massachusetts, Montana, New Hampshire, Oregon and Washington. The plant is very hardy (USDA zone 4, –30°F). The attractive and long-lasting ﬂowers are a potential economic crop (Liang et al., 2011; Zhang et al., 2007) (Figure 7.29). I. pseudacorus accumulates heavy metals and is reported to effectively remove pathogenic bacteria from wastewater (Tilley, 2011). Signiﬁcant amounts of cadmium and zinc were accumulated by I. pseudacorus according to one study, where the metal concentration in the plant increased as exposure to increasingly polluted water increased. Cadmium was concentrated in the roots and rhizomes, while zinc also accumulated in the leaves. These results suggest that this species is valuable for remediation of soils contaminated with heavy metals (Zhang et al., 2007). High yield from photosynthesis translates into long root length (18–20 cm). The root biomass of this Iris is moderate in diluted efﬂuent and low in full strength wastewater. The roots are very porous, which facilitates transfer of oxygen to the area around the roots. Accumulation of total nitrogen is high (moderate for ammonium but high for nitrate), for phosphorus accumulation is moderate (Li et al., 2013). This plant performs better in diluted than in full strength sewage, suggesting that
PLANTS IN CONSTRUCTED WETLANDS 119 Figure 7.29 Yellow flag iris, Iris pseudacorus, is one of the most highly ornamental of wetland plants. The flowers are 3–4 inches across. Photo: Gary Austin, 2015.
constructed wetland designs with a portion of recirculated efﬂuent might be most suitable. A microcosm study suggests that I. pseudacorus is a good choice for ﬂoating wetlands intended to remove nitrogen and phosphorus from surface water. In the study, Iris plants removed 277 mg of nitrogen per m2 per day and 9.32 mg of phosphorus per m2 per day during the growing season. The removal of 74 per cent of the total nitrogen and 60 per cent of the total phosphorous resulted from plant uptake (Caldelas et al., 2009). Iris sibirica, native to Turkey, Russia, and eastern and central Europe, grows 24–36 inches tall (60–90 cm) with highly ornamental blue or purple ﬂowers. I. sibirica appears to be a viable plant for use in constructed wetlands treating polluted river water according to a microcosm study (Li et al., 2013). An advantage of this species is its cold hardiness (USDA zone 4a, –34°F).
Sagittaria Three species of Sagittaria have been planted in constructed wetlands. Sagittaria latifolia, Common arrowhead (Figure 7.30), is distributed throughout the United States, southern and central Canada, Mexico, and is naturalized in Europe (USDA Zone 4a: (–30°F) to zone 11). Swans, geese, many species of ducks, and king rail eat the plant’s
120 PLANTS IN CONSTRUCTED WETLANDS Figure 7.30 Sagittaria latifolia, Common arrowhead. Photo: Mike Ryon License: government work product.
seeds and tubers, while muskrat, beaver and porcupine eat the tubers. The plant can be propagated by transplanting live plants or tubers or from seed, although it takes two years for the seed to germinate. Plants should be spaced 10–12 inches apart (25–30 cm) for full coverage within one growing season (Figure 7.31). The transplants should be covered with 1⁄2 inch of water until establishment. The mature plants are 18–24 inches tall and sustained by water 6–18 inches deep (0.15–0.45 m) where there is little or no current. S. latifolia was an important food source for indigenous people in the Americas. Sagittaria cuneata is a similar aquatic species (Stevens, 2003). In a microcosm study, this species grew well when exposed to nitrate, zinc, copper, lead and cadmium levels typical of urban stormwater (Kearney and Zhu, 2012). Ammonia levels below 200 mg/L are tolerated (Clarke and Baldwin, 2002).
Figure 7.31 Sagittaria latifolia. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
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Sagittaria lancifolia is native to Mexico, Central America and northern South America, and grows 24–36 inches tall (60–90 cm). The plants are easy to propagate by dividing rhizomes or by seed and ﬂourishes in USDA Zone 5a (–20°F) to zone 11. Sagittaria graminea is native to the United States and Canada, and grows in USDA Zone 5a (–20°F) to zone 9b. The grass-like leaves grow 18–24 inches (45–60 cm) or more in water 2–4 inches deep (2–10 cm).
Pontederia Pontederia cordata (P. sagittata), Pickerel weed (Figure 7.32), is native and widely distributed in North and South America and is hardy in USDA zones 5–11. Pickerel weed grows 2–3 feet tall with large erect leaves emerging from the base of the plant. The 6–8 inches long, purplish-blue ﬂower spikes bloom from May to October. Propagation is by seed or division. To establish by seed, distribute 20–30 seeds per square foot. The plant forms a mat of rhizomes and roots just below or covering the surface of the soil. The root mat and sturdy plant make this a valuable erosion control species. It tolerates ﬂooding to 20 inches deep, but permanent inundation only 6–12 inches deep, and tolerates salinity of only less than three parts per thousand. Birds feed on the seeds and the young leaves are edible (Miller, 2012). Pontederia cordata has a demonstrated capacity to grow in a subsurface ﬂow wetland receiving wastewater from a molasses distillery with high concentrations of BOD (533 mg/L), COD (1,181 mg/L) and SO4 (75 mg/L). This wetland achieved a concentration reduction of over 80 per cent for BOD and COD and 69 per cent for sulphate. This species also accumulates total Kjeldahl nitrogen equalling or exceeding Phragmites (Common reed) and Scirpus (Bulrush) (Olguín et al., 2008).
Caltha palustris Caltha palustris, marsh marigold (Figure 7.33), grows 2–18 inches (30–45 cm) in USDA Zone 3a (–40°F) to zone 11, and is widely distributed throughout the northern hemisphere. It has attractive yellow ﬂowers 1–2 inches (2–5 cm) in diameter. It grows
Figure 7.32 The coarse texture and the attractive flower make Pickerel weed, Pontederia cordata, a good choice where aesthetics is important and where water is shallow. Photo: Joshua Mayer. License: CC-BY-SA-2.0.
122 PLANTS IN CONSTRUCTED WETLANDS Figure 7.33 Caltha palustris, Marsh marigold, creates mats of dark green foliage with contrasting yellow flowers. Photo: Wildfeuer. License: CC-BY-SA-3.0.
in water 0–6 inches deep and tolerates shade. It is propagated by seed or by dividing the root ball. There are several hybrids in the nursery trade. C. palustris is much more sensitive to high sulphide concentrations than J. effusus.
Canna Canna indica is a highly ornamental wetland plant due to its large leaves (Figure 7.34) and showy ﬂowers that have been emphasized through the development of many hybrids. It is native to tropical Central and South America but naturalized across much of the globe including the south-eastern United States. It is frost tender and appropriate for USDA hardiness zone 8. Depending on the variety, the plant grows between 1.5 feet and 7.5 feet tal (0.5–2.5 m). Canna grows along streams and on disturbed land, but is often planted as an ornamental species in gardens and parks. C. Indica (Figure 7.35) preferentially accumulates nitrates rather than ammonium (Zhang, Rengel and Meney, 2009). C. indica is often planted in horizontal subsurface wetlands and performs well, as it can utilize nitrate as its nitrogen source for rapid growth. However, the plant uses ammonium when nitrate is less available and is commonly planted in free water surface and vertical subsurface wetlands. A study of Canna’s growth in the tropics estimated the accumulation of nitrogen at 0.57 g/m2 per day of which 0.23 g/m2 per day was translocated to the aboveground portions of the plant. These high rates of nitrogen accumulation in the leaves and stems allow the removal of an estimated 85 grams of nitrogen per m2 per year through annual harvest (Wang et al., 2014). Canna is an excellent plant for treatment of wastewater due to the length of its roots (18–20 cm), large root biomass and high yield of aboveground leaves and stems. It grows well in both diluted and undiluted septic tank efﬂuent (Li et al., 2013). The roots are thin (about 70 per cent are less than 1 mm in diameter) and ﬁbrous but abundant (Figure 7.36). This results in a large root area (22,832 cm2 per plant after
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Figure 7.34 Two Canna hybrid varieties within a shopping area wetland.
Figure 7.35 Canna indica is attractive due to its coarse texture and flower colour.
Photo: Gary Austin, 2015.
Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
Figure 7.36 Canna indica has long fibrous roots and spreads rapidly. It is reported to overwhelm Scirpus validus in a mixed planting (Calheiros et al., 2015). Photo: Maja Duamt. License: CC-BY-2.0.
21 weeks of cultivation in containers). This growth occurred with a 50 per cent dilution of domestic wastewater (COD – 76.08 ± 11.09 mg/L, total nitrogen – 11.43 ± 1.68 mg/L, total phosphorus – 0.56 ± 0.21 mg/L, phosphorus – 0.47 ± 0.20 mg/L, nitrate – 1.11 ± 0.01 mg/L, ammonium – 5.14 ± 1.13 mg/L) (Chen et al., 2007). Canna generalis grows in USDA zones 7b: 5°F (14.9°C) to 11, and is also native to South and Central America but common as an introduced plant in other tropical and subtropical areas including southeast United States. It has been investigated according to its ability to accumulate solvents and petroleum reﬁnery wastes. Benzene, toluene, ethylbenzene and xylenes are accumulated in the roots and rhizomes, and
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translocated to the shoots. At typical contamination levels, C. generalis is able to remove about 80 per cent of these pollutants from the root zone in 21 days (Boonsaner, Borrirukwisitsak and Boonsaner, 2011). Canna species have also been shown to remove heavy metals and pesticides. In conclusion, Canna is one of the best choices for constructed wetlands treating domestic sewage (Li et al., 2013), where it thrives in tropical and subtropical climates (Figure 7.37). In addition, since the plant and its hybrids are ornamental due to their ﬂowers and large, attractive leaves, Canna is valuable where aesthetics is an important function (Kearney and Zhu, 2012). Canna indica and other ornamental wetland plants (Canna ﬂaccida, Zantedeschia aethiopica, Canna indica, Agapanthus africanus and Watsonia borbonica) were planted in a horizontal subsurface wetland at a resort in Portugal. In addition to excellent wastewater treatment, the wetland provided attractive and cut ﬂowers for the facility (Calheiros et al., 2015). Figure 7.37 Canna ﬂaccida is native to southeast United States, where it grows in wetlands and is hardy to USDA zone 10. Photo: Peter A Mansfeld. License: CC-BY-SA-2.0.
Figure 7.38 Canna ﬂaccida in Florida. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
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Cyperus Cyperus papyrus (Figure 7.39) is characterized by 5 inch long (12 cm) roots, moderate root biomass but relatively high above ground biomass production. Its removal of COD is high and its removal of BOD is moderate, compared to other common high performance plants such as Canna and Iris. The accumulation of nitrogen is high, but the accumulation of phosphorus is relatively low (Li et al., 2013). One study demonstrated that the plant grew well when dissolved oxygen was limited (0.53–0.98 mg/L) (Kyambadde et al., 2004). A number of other species in this genus are planted in constructed wetlands in tropical climates including C. involucratus, Umbrella papyrus (Figure 7.40), which grows 4–6 feet (1.2–1.8 m) (USDA Zone 8a: to 10°F, –12.2°C). This attractive plant Figure 7.39 Cyperus papyrus is a soft textured, graceful plant that forms dense stands. Photo: Hans Hillewaert. License: CC-BY-SA-4.0.
Figure 7.40 A Laysan Albatross nestled in Cyperus involucratus on Sand Island, Midway Atoll. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
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is noteworthy for its ﬁne, ﬁbrous root system and good treatment performance. One free water surface microcosm study in subtropical China found that this plant developed more biomass in monoculture and mixed stands than Phragmites (Qiu et al., 2011), although a different microcosm study found its total biomass production to be lower than Phragmites australis or Canna indica (Li et al., 2013).
Arundo Arundo donax is native to eastern Asia, although it is globally distributed in tropical and subtropical climates. It grows 15–20 feet (4.7–6 m) in ﬂoodplains, but it also grows along low gradient streams in Mediterranean climates. Arundo donax grows in USDA zones 6a: 10°F (–23.3°C) to zone 10b. Giant reed (Figure 7.42) is capable
Figure 7.41 Cyperus papyrus. Growth has occurred on the surface, but without enough vertical roots in this subsurface gravel wetland. This may cause the plants to fall over and not contribute to the treatment process. The new shoots are removed and replanted. Photo: Heike Hoffmann, 2008. License: CC-BY-SA-2.0.
Figure 7.42 Arundo donax growing in northern California. Photo: USDA. License: government work product, CC-BY-SA-ND-2.0.
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of growing in reduced oxygen conditions due to long periods of inundation. It is potentially valuable as a lignocellulosic feedstock for paper pulp and manufacture of nylon due to its rapid growth, high biomass and since it is a non-food crop that grows in areas unsuitable for food production (Pompeiano et al., 2015). For these reasons, it also has potential as a feedstock for biofuel production. Experiments demonstrate that biofuel and biochar production is feasible (Saikia et al., 2015). A. donax performed well when planted in a horizontal subsurface ﬂow wetland in Morocco (El Hamouri, Nazih and Lahjouj, 2007). A. donaciformis is an endangered species that could be valuable in stormwater wetlands, where it is native in southern Europe. This use could mitigate the loss of wetland habitat in urban areas (Hardion et al., 2015).
Thalia Two species of Thalia are speciﬁed for use in constructed wetlands. The most ornamental is Thalia dealbata, Powdery Thalia (Figure 7.43). This dramatic tropical and subtropical plant grows in USDA zones 6a: 10°F (–23.3°C) to zone 10b. It grows 4–6 feet (1.2–1.8 m) tall, has large blue-green leaves and attractive purple ﬂowers. This species can tolerate water depths of 1.5 feet during the growing season and deeper water during the dormant season. Propagation is by division of rhizomes and seed. Seedlings should be planted 24 inches apart for full coverage in one growing season. New plants should be established with 1–2 inches water depth (water should not cover more than 2⁄3 of the shoot) (Moss, 2011). The plants should be established before contaminated water is added. T. dealbata has a demonstrated ability to ﬂourish in polluted river water and pretreated domestic sewage.
Figure 7.43 Thalia dealbata is a striking and versatile plant for treatment wetlands in warm climates. Photo: Gary Austin, 2015.
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T. geniculata, alligator ﬂag (Figure 7.44), is native to Africa, Central America and occurs in southeast United States. This species is taller (8–10 feet) and grows in USDA zones 7a (0°F, –17.7°C) to zone 10b. In one study, this plant grew very rapidly when transplanted into both horizontal subsurface and free water surface wetlands treating domestic sewage in El Salvador (Katsenovich et al., 2009).
Zantedeschia aethiopica Zantedeschia aethiopica, Calla lily (Figure 7.45), is a widely distributed plant native to southern and eastern Africa. It grows in aquatic as well as in terrestrial settings and is a common ornamental and market ﬂower in warm climates (USDA zones 8–10). The famous ﬂowers are white, yellow or light pink, standing slightly above large leaves. The plants grow rapidly (to 24 inches, 50 cm tall) in pretreated domestic sewage, producing substantial biomass and roots that are 10 inches long (25 cm) within a few months (Belmont and Metcalfe, 2003). Calla lily grew more vigorously in a horizontal subsurface ﬂow wetland than in a vertical subsurface ﬂow wetland setting when exposed to the same concentration of domestic sewage (Zurita, De Anda and Belmont, 2009). Zantedeschia aethiopica and Canna indica in a mixed planting, in a horizontal subsurface ﬂow wetland, performed as well as Typha latifolia in treating domestic sewage after pretreatment.
Heliconia There are several species of Heliconia that might be suitable for use in treatment wetlands. Heliconia psittacorum (Figure 7.46) has been investigated and shown to grow well in a horizontal subsurface ﬂow constructed wetland used to treat domestic wastewater. While its aesthetic and economic contributions are positive, this species performs much less well as a treatment plant compared to Canna indica in terms of root length, biomass, nitrogen accumulation, etc. (Konnerup, Koottatep and Brix, 2009). Therefore, it might be included as a subordinate planting in a constructed wetland and located where its beneﬁts can be appreciated and managed effectively.
Figure 7.44 Thalia geniculata. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
PLANTS IN CONSTRUCTED WETLANDS 129 Figure 7.45 Zantedeschia aethiopica. Photo: Carrie Kellenberger Hillewaert. License: CC-BY-2.0.
Figure 7.46 Heliconia psittacorum is a tropical and beautiful wetland plant with economic value. Photo: Pinus Hillewaert. License: CC-BY-SA-3.0.
Figure 7.47 Acorus gramineus, Japanese sweet flag, has attractive grass-like leaves 6–14 inches long (15–35.6 cm). Photo: Daderot. License: CC-BY-SA-3.0.
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Acorus gramineus Acorus gramineus (Figure 7.47), Japanese sweet ﬂag (USDA Zones 6–9), is a commonly planted ornamental plant native to eastern Asia. It grows in water 3–6 inches deep (7.6–15 cm) and is not tolerant of drought. It is uncommonly grown in constructed wetlands but can contribute to treatment wetlands while providing a commercial horticultural product (rhizomes can be divided in the spring). There are several varieties that have been developed for the ornamental landscape. A. gramineus is highly tolerant of domestic wastewater that also contains signiﬁcant concentrations of heavy metals (Zhang et al., 2007).
Agapanthus africanus Native to South Africa, A. africanus (Figure 7.48) grows 24–36 inches (60–90 cm) and features umbels of fragrant violet ﬂowers that are attractive to bees, butterﬂies and birds. It is hardy in USDA Zone 8a: 10°F (–12.2°C) to zone 11. Agapanthus growing in a vertical subsurface ﬂow wetland treating domestic sewage produced more leaves and more long-lasting ﬂowers than when growing under the same conditions in a horizontal subsurface ﬂow wetland (Zurita, De Anda and Belmont, 2009). In one study, more aggressive wetland plants, such as Phragmites, quickly overtook the Agapanthus. The plant does not require inundation, so it might be planted at the margin or even outside the treatment wetland rather than mixed randomly where its height and slower growth puts it at a disadvantage.
Strelitzia reginae S. reginae, Bird of paradise (Figure 7.49), is native to South Africa but is widely distributed in warm climates around the world. It grows in USDA zones 9b: 25°F (–3.8°C) to zone 11. The plant grows 4–6 feet tall (1.2–1.8 m) and 3 feet (1 m) wide with bold leaves and ﬂowers.
Figure 7.48 Agapanthus is a very attractive plant that is commonly grown as an ornamental plant in warm climates.
Figure 7.49 The exotic flowers of the bird of paradise make it an attractive prospect for vertical flow wetlands in warm climates.
Photo: Dezidor. License: CC-BY-SA-3.0.
Photo: Martina Nolte. License: CC-BY-SA-3.0.
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Growing in a vertical subsurface ﬂow wetland treating domestic sewage, S. reginae produced more and healthier ﬂowers and bigger leaves than when growing under the same conditions in a horizontal subsurface ﬂow wetland (Zurita, De Anda and Belmont, 2009). As with Agapanthus, this suggests that the species does not tolerate low-oxygen environments as well as other wetland species.
Watsonia borbonica W. borbonica, bugle lily (Figure 7.50), is a long-ﬂowering plant that is native to South Africa that grows in USDA zones 9a (20°F) to 10b. The plant is 4–5 feet tall with 2.5-inch long fragrant ﬂower spikes. The iris-like leaves are 2.5 feet tall. This species was grown successfully in a horizontal subsurface wetland treating domestic sewage (Calheiros et al., 2015). However, in its native range, it is often located in seasonal wetlands, suggesting that it would be useful in stormwater bio-retention basins. Figure 7.50 Watsonia borbonica blooms during the wet season and is dormant during the dry season in South Africa. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
Figure 7.51 Hymenocallis littoralis is another tropical and subtropical plant with good treatment capacity and outstanding visual appeal. Photo: Vicki. License: CC-BY2.0.
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Hymenocallis littoralis Spider lily is native to Latin America but has been introduced or naturalized in many tropical and subtropical regions (Figure 7.51). There are species of Hymenocallis that are native to southeast United States. The plant grows 18–24 inches (45–60 cm) with 5–7 inches long (14–17 cm) fragrant ﬂowers. Hybrids have been developed for the ornamental market. Spider lily grows in USDA zones 6a: –10°F (–23.3°C) to zone 11, and its growth rate and accumulation of root and aboveground biomass make it competitive with Canna ﬂaccida. Staged planting might allow it to compete with Phragmites and other fast growing wetland species. One study demonstrated that this species was effective in removing contaminants from seafood processing wastewater that was high in organic matter and nitrogen when planted in a free water surface wetland in Thailand (Sohsalam, Englande and Sirianuntapiboon, 2008).
Bacopa monnieri Bacopa monnieri, water hyssop, is native to India and Asia, but is globally distributed in warm climates including the southern tier of states in the United States. It grows in USDA zones 8a (10°F) to zone 11. It is a creeping perennial (Figure 7.52) but can be grown hydroponically and is tolerant of brackish water. It attracts bees, butterﬂies and birds. Propagation is through stem cuttings.
Colocasia esculenta Colocasia or Taro grows to 8 feet tall and wide. The heart-shaped leaves are 2–3 feet long and 1–2 feet wide on 3-feet-long stems that all emerge from a corm that can weight 1–2 pounds (Figure 7.53). The corms, stems and the young leaves are edible and nutritious. There are more than 200 cultivars of Taro; some best suited to wetlands
Figure 7.52 Bacopa Monnieri, Water hyssop. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
PLANTS IN CONSTRUCTED WETLANDS 133 Figure 7.53 Colocasia esculenta grows in USDA hardiness zones 8a (10 °F, –12.2 °C) to 11. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
and others better suited to unﬂooded ﬁelds. Other cultivars highlight ornamental characteristics, such as foliage colour. In wetlands, Taro is planted 18 inches apart (45 cm) resulting in 20,400 plants per acre (49,000 per hectare). Taro is propagated by collecting the small corms with stems that form around the main corm. The small corms are planted 12 inches deep (30 cm). A number of insects and other pests attack the plants (Moore and Lawrence, 2003). The corms of Taro are known to accumulate arsenic, cadmium, lead and mercury from landﬁll leachate and mining wastewater (Madera-Parra et al., 2015). Colocasia has been grown successfully in horizontal subsurface ﬂow wetlands with domestic sewage with COD levels as high as 1650 mg/L.
Floating wetland plants This group of wetland plants ﬂoats freely on the surface of lakes, ponds and slow moving surface water. They have relatively short roots that take nutrients directly from the water column.
Eichhornia crassipes Water hyacinth is native to tropical America but is naturalized and invasive in the southeast United States and warm climates around the world. The glossy spoon-shaped leaves are attached to spongy stems with nodules (Figure 7.54) that keep the plant aﬂoat. The ﬁne roots hang a foot or more into the water. The showy ﬂowers are violet with yellow spots, and stand on 6-inch spikes above the foliage (attractive as cut ﬂowers) (Figure 7.55). Water hyacinth grows in full sun and requires at least 50°F to produce new growth. It survives freezing and grows in USDA zone 9a: –6.6°C (20°F) to zone 10b. Where it is invasive, it can spread with alarming swiftness, doubling or
134 PLANTS IN CONSTRUCTED WETLANDS Figure 7.54 Eichhornia crassipes has bladder-like nodules that make the plant buoyant. Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
Figure 7.55 The beautiful water hyacinth flower and attractive foliage complement the plant’s wastewater treatment effectiveness. Photo: Wouter Hagens. License: public domain.
quadrupling its population in as little as 2 weeks, creating signiﬁcant ecosystem impact. It can create 200 tons of biomass per acre. Laboratory and pilot scale studies demonstrate that water hyacinth and water lettuce (Pistia stratiotes) can be used in a recirculating, aerated system to treat domestic wastewater to secondary standards within 2 to 4.5 days (or 7–8 days without circulation and aeration) (Zimmels, Kirzhner and Kadmon, 2009). The plant absorbs nitrogen and phosphorus into its roots and leaves and is a very effective accumulator of heavy metals. Since E. crassipes increases biomass very rapidly, frequent harvesting is an effective way to remove nutrients and metals from wastewater (Marchand et al., 2010). E. crassipes is also capable of reducing industrial pollutants. The plant is more tolerant of cyanide than many plants. For example, Salix viminalis (willow) was killed by an 8 mg/L concentration. Water hyacinth was able to tolerate and entirely remove a 10 mg/L concentration of cyanide within a 23–32-hour treatment period (Ebel, Evangelou and Schaeffer, 2007). This capability makes the plant valuable for treating cyanide efﬂuent from small-scale gold mining efﬂuent.
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Naphthalene (a polycyclic aromatic hydrocarbon, PAH) is another industrial pollutant known to cause cancer. At a concentration of 13 mg/L, naphthalene was completely removed by water hyacinth during a 9-day treatment period (NesterenkoMalkovskaya et al., 2012).
Pistia stratiotes Pistia stratiotes, Water lettuce (Figure 7.56), is native to Africa but is now distributed in virtually all tropical and subtropical freshwater habitats. This plant forms 6-inch wide rosettes of leaves and has 50-cm-long roots. It grows only in warm climates (USDA Zone 9a: 20°F, –6.6°C). Water lettuce is a particularly effective accumulator of mercury and chromium from polluted water.
Lemna minor L. minor is native to the United States and Canada and widely distributed elsewhere (Figure 7.57). This tiny plant, just 1⁄4 inch in diameter (2–5 mm), grows in USDA zone 5a: –20°F (–28.8°C) to zone 11 and reproduces rapidly, although it is shortFigure 7.56 Pistia stratiotes, water lettuce, is an attractive free-floating plant common in warm climates Photo: Forest and Kim Starr. License: CC-BY-SA-3.0.
Figure 7.57 Lemna minor, duckweed, is a tiny but prolific floating plant. Photo: Barbarossa. License: CC-BY-SA-3.0.
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lived (about 30 days). There are even commercial Lemna farms, as it is possible to produce 10–30 tons of dried duckweed per hectare per year. The crop is high in protein and is used for cattle feed. The feed contains 25–45 per cent proteins (depending on the growth conditions), 4.4 per cent fat and 8–10 per cent ﬁbre, measured by dry weight. In natural and constructed wetlands Lemna is an important food for ﬁsh and waterfowl. From a distance, this plant can appear to be an algae mat, but is actually indicative of fairly good water quality, while an algae mat often indicates a eutrophic problem. A free water surface wetland with L. minor for tertiary treatment of domestic wastewater was compared in a 3-year Turkish study with a horizontal subsurface ﬂow wetland planted with Cyperus and surface ﬂow constructed wetland planted with Cyperus. The Lemna wetland achieved a comparable performance, although the required hydraulic residence time was more than twice as long (Ayaz, 2008). Lemna minor demonstrates the ability to grow in ethanol and citric acid production wastewater with COD as high as 1,400 mg/L, which could not be tolerated by Eichhornia crassipes (water hyacinth), Azolla ﬁliculoides (water fern), Salvinia Rotundifolia willd (water fern) and Wolfﬁa columbiana (duckweed) (Valderrama et al., 2002). It tolerates chromium at 2 mg/L and is an effective accumulator (Uysal, 2013). Lemna minor has also been studied for the treatment of distillery efﬂuent where COD and BOD concentrations were very high at 17,540 and 25,576 mg/L, respectively. Lemna provided better treatment than water hyacinth (Ran, Agami and Oron, 2004). Lemna gibba is very similar to L. minor but is distributed throughout Europe, Africa and South America.
Planting design Where treatment wetlands are constructed in a public setting, such as in the Bridged Gardens, Tianjin, China, or Houtan Park, Shanghai, China, the beauty of the planting design is nearly as important as the treatment effectiveness. For example, at a guest house in Portugal, a horizontal subsurface ﬂow wetland to treat domestic sewage was planted with ornamental ﬂowering plants (Canna ﬂaccida, Zantedeschia aethiopica, Canna indica, Agapanthus africanus and Watsonia borbonica). The ﬂowers were harvested for use as decoration inside the buildings. The Agapanthus grew slowly and was overwhelmed by the more vigorous species, suggesting the need for a staged installation of plants. The treatment performance was very good, although only the Canna is a common treatment plant. Removal of BOD and COD were more than 90 per cent, and removal of phosphorus, ammonium and total coliform bacteria were as much as 92 per cent, 84 per cent and 99 per cent respectively (Calheiros et al., 2015). Planting design examples are available for free water surface constructed wetlands (Figure 7.58), but much more research and many demonstration projects are required to apply effective methods to horizontal and vertical subsurface ﬂow wetlands. Generally, these have been planted as monocultures with very few of the many possible plants attempted. Similarly, the development of niches for wetland plants that are not part of the treatment system but adjacent to the treatment basins is a relatively unexplored opportunity to increase the diversity of the planting palette and target ecosystem restoration and enhancement goals. Again, habitat wetlands tangentially associated with wastewater treatment have been constructed in free water surface wetland sequences, but have not been created adjacent to the subsurface ﬂow types.
PLANTS IN CONSTRUCTED WETLANDS 137 Figure 7.58 High plant diversity with species organized in masses and according to water depth and frequency of inundation creates a maintainable and beautiful landscape. Attention to the texture, blossom colour and form of the plants establishes dynamic and attractive scenes. Photo: Gary Austin, 2015, Turenscape planting design.
See the Appendices for plant lists organized by continent and for lists of plants installed in projects in differing climates.
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8 Riparian wetlands Introduction This chapter begins a new section in which we review recently constructed wetlands intended to solve pollution, urban and environmental problems, in order to assess the wetlands’ successes and shortcomings. In every case, constructed riparian wetlands should achieve multiple objectives. This is most apparent when riparian wetlands are fashioned or restored in the urban environment (Figures 8.1 and 8.2). In these cases, every category of ecosystem service should be advanced, in addition to ecosystem health and biological diversity. The Millennium Ecosystem Assessment (Hassan et al., 2005) divided ecosystem services into provisioning, regulating, supporting and cultural categories. Ecosystem services are human beneﬁts. The beneﬁts ﬂow to humans only through viable biotic and abiotic networks. Therefore, planners and designers of constructed wetlands must generate, restore or sustain wetland ecosystem functions on-site and off-site in order to maximize human beneﬁt and ecosystem health. Despite the holistic imperative of the introduction above, the next few paragraphs will address individual objectives before the case studies illustrate how these can be integrated and mutually supportive. Riparian constructed wetlands are often employed to remediate polluted water. The source of pollution and the intended use of the repaired waters vary. Within agricultural landscapes, the removal of pesticides and other contamination associated with the application of artiﬁcial fertilizers may be undertaken to reduce impacts on aquatic ecosystems and to recover habitat previously lost due to ﬁlling and channelization. The Des Plains River wetland restoration in Illinois is a constructed wetlands project of this type (Kostel et al., 2012). Of course, the scale and length of rivers means that pollutants can be transported over long distances and can impact remote urban, natural and even oceanic environments. Another motivation for the creation of riparian wetlands is to improve the quality of water in rivers that serve as the drinking water source for downstream towns and cities. River water is always treated before use as drinking water, but the difﬁculty and cost of treatment to potable standards is far more difﬁcult and expensive if the inﬂuent is highly contaminated. The experience of New York City is a welldocumented example demonstrating that preventing pollution of the drinking water source is far less expensive than treating polluted water to create drinking water (New York City Department of Environmental Protection, 2012; DePalma, 2006). Water from mine tailings, uncontrolled industrial discharges, inadequately treated domestic sewage from wastewater treatment plants, or leaking septic tanks and drain
RIPARIAN WETLANDS 143 Figure 8.1 The Sanlihe River restoration project removed concrete channel walls, repaired the hydrological function by: routing some water from the larger Luan River, removing solid waste dumps, and preventing the inflow of poorly treated sewage and treatment of urban stormwater run-off before it entered the restored river. The creation of multiple channels allowed the retention of rows of existing trees while expanding the floodway. Photo: Kongjian Yu, 2014.
Figure 8.2 Before 2007, this river was a concrete channel. Polluted by industrial discharges and eventually depleted of water due to industry, agriculture and urban withdrawals, the river had become a wasteland and civic liability. The Sanlihe River Ecological Corridor Project by Turenscape reversed the history of pollution and transformed the river into an ecological and community resource. The restored river is 8.3 miles long (13.4 km), 330–980 feet wide (100–300 m) with a total area of 333 acres (135 hectares). Photo: Kongjian Yu, 2014.
ﬁelds can all contribute polluted water to streams and rivers. The degradation of rivers from these many discharges can produce pollution levels that challenge the technology and economics of removal for human use. While surface water quality standards for swimming, wading, ﬁshing, boating and other recreational contact are lower than the requirements for drinking water, rivers often fail to meet these standards. Of most concern are substances in the water that threaten to make people sick in the short or long term. Pathogenic bacteria from livestock operations, inadequately treated human sewage and urban stormwater run-off regularly require the closure of rivers, lakes and coastal beaches for recreational use.
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Finally, there are several contaminants and excess nutrients that ﬁnd their way to rivers through urban stormwater run-off. Many of these are associated with the pervasive use of the private automobile, which contributes polycyclic aromatic hydrocarbons (PAH), polychlorinated bi-phenyl hydrocarbons and other cancercausing substances. Heavy metals such as cadmium, lead, copper and zinc are also associated with automobiles and run-off from industrial land uses. Urban and suburban stormwater run-off also contains surprisingly large quantities of pathogenic bacteria, nitrogen and phosphorous, which compromise human health and the functions of aquatic ecosystems. Is the river margin really the best location for reducing water pollution in rivers? Absolutely not. A better strategy is to reduce pollution at its source, before it reaches natural streams and rivers. Unfortunately, rivers have served humans as convenient waste disposal systems for millenniums. Many energy, chemical, consumer product and commodity agricultural industries seek the water supply, waste disposal and transportation opportunities offered by rivers. Therefore, the use of riparian wetlands to treat river water is a remedial practice, suggesting the absence of comprehensive treatment policies for industrial discharge, municipal sewage efﬂuent and non-point source pollution. The broad range of contaminants from these diverse pollution sources makes the improvement of water quality more challenging than when engineering for a narrower range of substances associated with homogeneous land uses. However, the use of constructed riparian wetlands for treatment of point or nonpoint sources of contaminated water generated on adjacent parcels, such a stormwater run-off from a neighbourhood, is a preventative rather than remedial practice. This is the situation on the margins of the Sanlihe River, as illustrated in Figure 8.2.
Alteration of rivers Unfortunately, there are relatively few free-ﬂowing rivers in the world. Urbanization, agriculture and energy demands inspired channelization and damming rivers to control ﬂooding and provide local economic opportunities (Figure 8.3). During the last few centuries, these changes have sometimes been engineered without a comprehensive understanding of regional hydrology, resulting in adverse impacts, as illustrated by the history of the lower Mississippi River in the United States and the Yangtze River
Figure 8.3 The first image shows the existing condition of the Arroyo Secco River Channel at the confluence with the Los Angeles River. The second image is a photo simulation of a proposed revision of the same area. Photo: US Army Corps of Engineers. License: public domain.
RIPARIAN WETLANDS 145
in China. River control efforts have often resulted in unintended consequences, costing human lives and economic hardship. Historically, cities were located along rivers for defensive, transportation, agricultural and industrial purposes. More recently, rivers attract urban dwellers for the recreation and aesthetic advantages that they offer. Associated with this history of human use of rivers is their modiﬁcation for human purposes. The practice of ﬂood prevention through channelization, levees, dredging, dams and ﬂoodgates is a global activity. Similarly, the ﬁlling and hardening of the river edge to serve as development pads and docking infrastructure is common in all cities built along rivers. In most cities of this sort, much damage is done, and reversing it will take decades. For example, 35 million euros were spent to eliminate contaminants and debris left from World War II, improve ﬂood control and provide recreation and habitat along the Isar River in Munich, Germany (Figure 8.4) (RESTORE, 2013). We must avail ourselves of all opportunities to implement palliative and preventive measures if rivers are to be clean enough for human use and clean enough to support healthy aquatic ecosystems.
Achievable objectives Riparian constructed wetlands can signiﬁcantly improve the quality of water in rivers if they are frequent and extensive, but the water quality goals should not blind us to the many other achievable objectives. Flood hazard protection is a common secondary beneﬁt of constructed wetlands. A natural associated objective is ecosystem health and enhanced biological diversity. In urban areas, provisions for open space, recreation opportunities, social spaces and educational resources constitute the long list of
Figure 8.4 The Isar River flows through Munich, Germany. The city removed the walls channelizing the river. To fortify the riverbanks, sheet piles were installed at the edge of the floodplain. Soil was filled against these to establish a naturalistic bank while providing flood protection. Habitat by planting native vegetation and new recreation opportunities resulted from public access points and new beaches. Water quality is further improved by the more natural river. Photo: Bbb. License: CC-BY-SA-3.0.
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cultural services that could be generated. Important among these cultural services is the prospect of increased tourism and economic development. A less obvious objective might be provisioning ecosystem services. Fish, crayﬁsh and shellﬁsh are examples of foods that could be greatly expanded. In addition, we could include crops grown on the upland benches of the wetland. Even ﬁbre from poplar trees, willows or wetland vegetation, such as common reed, could be cultivated as feedstock for paper, biofuels or other products. Finally, as suggested earlier, elimination of disease-causing organisms, the cycling of nutrients, carbon sequestration, soil formation and other regulating and supporting ecosystem services should not be discounted processes and products of the constructed wetland.
Natural riparian wetlands Free-ﬂowing rivers exhibit a range of edge conditions depending on the gradient of the bed and the bed material. The amount of seasonal change in the water level also contributes to a range of edge characteristics. In nearly every case, there is a linear riparian habitat that extends some distance from the edge of the water (Figure 8.5). Greater humidity, access to groundwater or annual inundation all inﬂuence the vegetation communities, which differ from the adjacent upland vegetation associations. The vegetation along rivers is not necessarily wetland plants, but low-lying lands adjacent to a river that ﬂoods seasonally or where there is high groundwater develop into wetlands of various types. These are often associated with a historic route of the river that has been forsaken for a new main stem route (Figure 8.6). A natural linear wetland is the model for constructed riparian wetlands presented in this chapter.
General characteristics of riparian constructed wetlands In order to repair hydrological damage, restore habitat or treat polluted water, riparian constructed wetlands are increasingly necessary. The distinction between linear constructed wetlands and others is somewhat artiﬁcial. Broad wetlands, either natural or engineered, are commonly associated with rivers (Figure 8.7), but the linearity of constructed riparian wetlands presents particular opportunities and challenges.
Figure 8.5 Natural riparian vegetation. Photo: Dave Powell. License: CC-BY-SA-3.0.
RIPARIAN WETLANDS 147 Figure 8.6 Riparian wetlands along and within rivers and streams develop due to natural sedimentation and changes in the course of the river. Photo: P reIgor. License: CC-BYSA-2.0.
Figure 8.7 Wetlands along the Kobuk River, Alaska. Photo: Neal Herbert, NPS Alaska Region. License: CC-BY-SA-2.0.
Riparian constructed wetlands are formed by creating a side channel separated from the main stem of the river, similar to patterns seen in braided natural rivers. The main stem feeds the riparian constructed wetland, and the long narrow shape favours sedimentation and ﬁltration processes. In the developed urban or agricultural landscape, linear wetlands are often the most viable spatial option. For example, many urban rivers in the United States were engineered to ﬂow within concrete channels with a trapezoidal cross section (Figure 8.8). Restoring ecosystem values along these rivers often requires replacing the angled wall with a vertical wall to generate space along the edge of the water for wetland vegetation. Even removing the concrete bed often results in vegetation growth and improved biodiversity. In other cases, railroad corridors or highways following rivers have been relocated to recover narrow strips along the river for restoration efforts. Extending the width of the channel is also an important retroﬁt strategy for tidal inﬂuenced rivers subjected to increasing water level due to global warming. In fact, this technique is often necessary to adapt to increasing stormwater run-off volume associated with global warming for streams and rivers away from the coast (Figure 8.4).
148 RIPARIAN WETLANDS Figure 8.8 Efforts are underway to restore portions of the Los Angeles River in this condition to a more natural configuration. Photo: Downtowngal. License: CC-BY-SA-3.0.
Multifunctional riparian constructed wetlands For the reduction of pollution, the shape of the linear wetland is well suited for removal of suspended solids, and sequestration of heavy metals and petroleum aromatic hydrocarbons, but is less well suited for the removal of dissolved metals or nitrates, for example. However, special design measures can overcome this shortcoming. Recreation trails and gathering areas for small groups are easily accommodated along the linear wetland (Figure 8.9), but activities requiring more expansive space are less well served. Wetland habitat is particularly rich due to the presence of water and the heterogeneous mosaic created through the interaction with upland vegetation. However, the narrow strip will be inadequate for animal species that require large territories or those that are sensitive to the presence of humans, if the wetland is in the urban or suburban landscape. Again, urban biological diversity can be maximized through the application of design measures. Perhaps, most important is the role the constructed riparian wetland can play as a corridor that connects more expansive and more natural habitat within and beyond the city (Figure 8.1). Reducing ﬂood hazard is highly compatible with the other functions of constructed riparian wetlands, as illustrated in the Isar River (Figure 8.4) and the Houtan Park case studies.
Houtan Park case study Huangpu River The Huangpu River is 70 miles long with its headwaters in an agricultural area upstream from Shanghai, China. As it ﬂows toward the city, agriculture becomes mixed with residential and small manufacturing enterprises (Figure 8.10). It is within this reach that Shanghai diverts ﬁve million cubic metres of river water to treatment plants for puriﬁcation to drinking water standards. The quality of the water in the river is declining because of point and non-point source pollution. Agricultural run-off containing fertilizer, poorly treated sewage from small towns, industrial discharges and its location downstream from the polluted Lake Taihu all contribute to the poor water quality at the drinking water intake. At the intake, the concentration of total
RIPARIAN WETLANDS 149 Figure 8.9 Public health, ecosystem restoration and social opportunities are three of the many values evident in this photograph of the constructed wetland along the Tanghe River. Photo: Kongjian Yu.
Figure 8.10 Huangpu River upstream from Shanghai. Notice the high volume of shipping traffic. Image: Google Earth and DigiGlobe 11/13/2014, 30°8′47.31″ N 121°19′46.01″ E, image accessed: 18 February 2014.
suspended solids ((TSS) an indirect measure of pollution) is between 50 and 150 mg/L. A desirable level is less than 30 mg/L. Disinfection of the river water requires increasingly large amounts of chlorine, which interacts with the large amount of dissolved organic matter in the river water to create harmful compounds that are delivered with the drinking water to the residents of the city (Xu et al., 2007). Unfortunately, the quality of the river water continues to worsen as it ﬂows toward Shanghai. As the river approaches the city, energy and industrial plants burning coal are common along the banks (Figure 8.11), while highly impervious residential and commercial districts contribute non-point source pollution from locations further from the river. Toward the centre of the city, the industrial uses are being replaced by highdensity, mixed-use developments. Coal-ﬁred power plants discharge phenols, which accumulate in the bottom sediment of the river and are harmful to ﬁsh and people. Phenol is carbolic acid, a
150 RIPARIAN WETLANDS Figure 8.11 Coal-fired energy and industrial plants along the Huangpu River. Image: Google Earth and DigitalGlobe 9 February 2015, 31°03′33.58″ N 121°28′15.65″ E, image accessed: 18 February 2014.
common manufacturing chemical used to produce fertilizer and paint. It is a solvent and a product of coal tar. PAH have toxic, mutagenic and carcinogenic characteristics. About 40 per cent of the PAH in the Huangpu River are from coal combustion, while trafﬁc-related pollution and spills of oil products contribute 36 per cent and 24 per cent, respectively. Escherichia coli (E. coli), a human pathogen (and a commonly used indicator of the presence of many other pathogens), is present in high concentration near the centre of Shanghai. Here, there are between 3,000 to a little less than 30,000 colony-forming units (CFU) per 100 ml. This level can be compared to the US Environmental Protection Agency (EPA) standard of 126 CFU per 100 ml of E. coli for primary recreational contact (swimming). As contaminant levels in river water increase, a dynamic arises in which high levels of ammonium and organic material cause explosive growth of bacteria that reduce dissolved oxygen to levels that threaten ﬁsh and other aquatic species. Low oxygen levels also reduce the conversion of ammonia to nitrate and the transformation of nitrate into nitrogen gas and harmless by-products. These processes are critical to effective pollution mitigation (Dong Yue et al., 2013). Table 8.1 summarizes the compromised water quality of the Huangpu River in the area of the drinking water intake (upstream) (Figure 8.10) and in the area of Houtan Park (city centre) (Figure 8.12). The range of values in the table indicates seasonal variations due to increased dilution of pollutants during the rainy season.
RIPARIAN WETLANDS 151 Table 8.1 Huangpu River water quality
TSS BOD DO TN TP NH4 NO3 E. coli Phenol Oil
50–150 1.2–2.3 4–9 3.5–5 0.3–0.5 0.5–2 1–1.8 Meets Std 0.001–0.003 0.1–0.16
100–350 4.8 -9.8 1.2–3 3–6 0.23–0.38 1.8–4.8 0.2–0.6 3,000–30,000 0.001–0.006 0.18–1.2
30 (30) 30 (30) 6 (4–5) 0.5 (4) 0.1 0.5 (0.4) (10) (126*)
All units Mg/L, except E. coli. Standard – Chinese (US EPA). TSS – total suspended solids; BOD – biological oxygen demand; DO – dissolved oxygen; TN – total nitrogen; TP – total phosphorous; NH4 – ammonium; NO3 – nitrate. * colony-forming units meeting primary recreational contact.
Figure 8.12 Aerial view of Houtan Park along the bank of the Huangpu River near the centre of Shanghai. Image: Google Earth and DigitalGlobe 10 October 2015, 31°11′11.22″ N 121°28′08.93″ E, image accessed: 18 February 2014
The water quality improvement goals for Houtan Park should have targeted those contaminants posing the highest risk to human and aquatic health. Therefore, reducing the high concentrations of E. coli, TSS, total phosphorous (TP) and ammonium is most important, as is increasing the amount of dissolved oxygen in the river water. The levels of most of these contaminants are quite high, compared to levels in European rivers (European Environment Agency, 2015), for example.
The Houtan Park context Houtan Park is located in the Pudong area of Shanghai on Shibo Avenue and near the North-South Elevated Road (31°11′10.62″ N 121°28′12.25″ E). Houtan Park follows the bank of the Huangpu River, which is an average of 1,300 feet wide (400 m) and 30 feet deep (9 m), dividing Shanghai into two parts. Near the heart of the city, the area around the park is being rapidly redeveloped. Former industrial and warehousing operations are being replaced by high-density and mixed-use urban districts (Figure 8.13). The site of the park was formerly a steel factory and shipyard. Subsequent use of the parcel as a landﬁll and industrial staging yard continued a legacy
152 RIPARIAN WETLANDS Figure 8.13 Houtan Park along the bank of the Huangpu River near the centre of Shanghai. Photo: Kongjian Yu, 2014.
Figure 8.14 The industrial riverbank of the Huangpu River at the proposed location of Houtan Park. Note the vertical floodwall. This was removed when the new park was constructed. Photo: Kongjian Yu, 2008.
of soil and river contamination (Figure 8.20). A vertical ﬂood control wall separated the parcel from the river. In fact, the site of the future park and constructed wetland lay between the 20-year and 1,000-year ﬂood control structures. The Huangpu River is inﬂuenced by tidal ﬂows at this location, causing the water to ﬂuctuate 6 feet (2 m), establishing an inaccessible, muddy and littered river edge (Figure 8.14). The site is long and narrow, between 100 and 265 feet wide, and features an 18-foot elevation
RIPARIAN WETLANDS 153
change between the shoreline and the road. The total area of the park is 34.6 acres (14 hectares), and the length of the water treatment sequence is 1 mile (1.7 km).
Design programme There was an extensive programme for the project, as the purpose of the park was to change in emphasis over time. The initial impetus for the project was the Shanghai Exposition hosted by China in 2010. Many international pavilions were planned (Figure 8.15). Some of the thousands of visitors to the exposition would arrive by ferry. Therefore, the park includes a dock, embarkation structure and a ceremonial walkway to the pavilion area. The planners of the exposition followed the international tradition of highlighting technology and sustainable development, including a demonstration of the biological treatment of polluted river water (Figure 8.17). The treated water was to be used in the pools and fountains within the pavilion area (Figure 8.16). The park included structures for displays, restrooms, walking paths and gathering areas. The landscape architect adopted and extended the sustainability theme of the project to include the reuse of existing structures and materials, the creation of new habitat for birds, wildlife and aquatic organisms, and the cultivation of crops. This programme was in addition to providing ﬂood mitigation and reduction of stormwater run-off. The following sections document the design and performance of Houtan Park, beginning with a review of water quality and biodiversity improvements. Figure 8.15 The Chinese Pavilion at the 2010 Shanghai Exposition. Photo: Brücke Osteuropa, 2010. License: CC public domain.
Figure 8.16 The main axis of the Shanghai Exposition with pools filled with treated river water. Photo: Suzuki, 2010. License: CC-BY-2.0.
154 RIPARIAN WETLANDS Figure 8.17 This image illustrates the suspended solids in the water in the first and the last stage of the wetland. Photo: Kongjian Yu, 2010.
Table 8.2 Project calendar
Water introduced Initial planting Second planting First fish, shellfish and other aquatic organisms introduced Wetland establishment period Exposition open Maintenance assisted period with water quality testing Mature wetland (reduced maintenance) with water quality testing
6, 2009 6, 2009 10, 2009 10, 2009 6, 2009 to 12, 2009 5, 2010 to 10, 2010 6, 2009 to 10, 2010 11, 2010 to 10, 2012
Programme implementation The implementation of the wetland was conceptualized in three stages with stage one (Figure 8.18) located nearest to the head of the wetland and featuring plants and other organisms most resistant to high levels of pollution. Water was introduced for the ﬁrst time in June 2009 and followed by a 6-month start-up and stabilization period (Table 8.2). In October 2009, the ﬁrst ﬁsh, aquatic snails and shrimp were introduced. Twenty-eight species of wetland plants were planted in the wetland (Figures 8.19 and 8.22). Those adapted to living in polluted water were introduced ﬁrst. Thousands of plants from three species dominated the initial planting. Twenty-ﬁve thousand common reed (Phragmites australis), 15,000 eelgrass (Vallisneria natans), and 12,000 waterthyme (Hydrilla verticilata) were planted. The plants were carefully selected so that there were species active in every season with special attention to plants that would be actively growing during the winter. No invasive plants were included in the planting palette. Twenty-two species of aquatic organisms were introduced. The 1,000 Asian clams (Corbicula ﬂuminea) represented the greatest number of individuals for any species.
Water treatment This constructed wetland treats a small fraction of the water volume that ﬂows past the park (Figure 8.24). Nevertheless, riparian treatment wetlands mitigate existing pollution (Figures 8.19 and 8.22), and the huge volumes of polluted water in the river call for many more extensive riparian wetlands within the urban area. The daily ﬂow
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Figure 8.18 Constructed wetland plan with contours. The river water enters on the left and travels through a series of cells that target particular contaminants. Image: Kongjian Yu, 2009.
Figure 8.19 The planting design for Houtan Park is in contrast to the monocultures that characterize most constructed wetlands projects. This image shows a broad range of submerged, floating leaf and emergent plant species that contribute to the treatment of the polluted river water. Photo: Kongjian Yu, 2014.
into the wetland is 2,500 m3 (660,430 gallons), while the outﬂow is 2,400 m3. The difference represents a 100 m3 per day loss, due to evapotranspiration and inﬁltration. A study of the water quality performance of the constructed wetlands in Houtan Park was conducted between 2009 and 2012. The analysis included testing before and after the plants were established. The water quality testing was divided into an establishment phase (June 2009–October 2010) and a mature phase (November 2010– October 2011). The ﬁrst phase included more intensive maintenance of the plants, particularly harvesting of the wetland vegetation in autumn. During both phases, three water samples were collected every month from 10 different points distributed along the water route. The water quality was characterized according to an index that included un-ionized ammonia (NH3), chemical oxygen demand (COD), nitrite (NO2), nitrate (NO3), total nitrogen (TN) and TP (Dong Yue et al., 2013). Unfortunately, the index did not include measurements for biological oxygen demand (BOD), TSS, heavy metals, PAH or pathogenic bacteria, which are either important indirect or direct measures of water pollution in the United States. Using the composite measure of water quality, the constructed wetland results in a general water quality improvement (Figure 8.17) changing from the Chinese standard Class 5–4 to Class 3–2. There are ﬁve water quality standards deﬁned by the Chinese government (Table 8.3).
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• • • • •
Class 1: Consistent with protected natural landscapes. Excellent drinking water quality. Class 2: Surface water for drinking purpose (1st grade protection area), water for aquaculture (precious species). Class 3: Surface water for drinking purpose (2nd grade protection area), water for aquaculture (common species). Class 4: Suitable for industrial use. Class 5: Suitable for industrial use. Unsuitable for human contact (Wang et al., 2012).
When reviewing the individual constituents, it’s clear that some contaminants were more effectively removed than others. Nitrogen improved from Class 5 to 4–3; TP improved from Class 4 to 2; COD and ammonia met the Class 3 standard, while DO improved signiﬁcantly from Class 3 to 1. The 86.4 per cent reduction in nitrate was dramatic and accounts for the reduction in TN. COD is a water quality indicator often used for water that contains constituents from industrial land uses. The test for COD uses a chemical (such as potassium dichromate) to deﬁne the oxygen demand required for degradation of both organic and inorganic matter in the water sample. Since BOD measures only the oxygen demand to degrade organic matter and COD is a measure of both organic and inorganic demand, COD values are always higher than BOD values. When BOD is near 0, COD is approximately 50. If BOD/COD ratio is 0.5, then the wastewater is easily treatable by biological means. There was little reduction in the amount of ammonia, which explains the small reduction of TN (25 per cent). This result is consistent with free water surface wetlands (Kadlec, 2009). Vertical ﬂow constructed wetlands demonstrate as much as 80 per cent removal of ammonia, relying on bacteria rather than plant uptake, although this wetland type is also planted. Replacing some of the free water surface Table 8.3 Chinese water quality standards. All units = mg/L, except faecal coliform – number/litre
BOD5 COD ≤ TSS ≤ TP ≤b TN ≤ TOC Ammonium NH4 DO ≥ Faecal coliform Copper (Cu) Zinc (Zn) Petroleum Chlorine
China Class 1
3 15 20 0.02 0.2 20 15 7.5 200 0.01 2 50 75%) Impervious areas: Paved parking lots, roofs, driveways, etc. (excluding right-of-way) Streets and roads: Paved; curbs and storm sewers (excluding right-of-way) Paved; open ditches (including right-of-way) Gravel (including right-of-way) Dirt (including right-of-way) Western desert urban areas: Natural desert landscaping (pervious areas only) 4/ Artificial desert landscaping (impervious weed barrier, desert shrub with 1″–2″ sand or gravel mulch and basin borders)
68 49 39
79 69 61
86 79 74
89 84 80
98 83 76 72
98 89 85 82
98 92 89 87
98 93 91 89
Urban districts: Commercial and business Industrial
Residential districts by average lot size: 1 ⁄8 acre or less (town houses) 1 ⁄4 acre 1 ⁄3 acre 1 ⁄2 acre 1 acre 2 acres
65 38 30 25 20 12
77 61 57 54 51 46
85 75 72 70 68 65
90 83 81 80 79 77
92 87 86 85 84 82
Developing urban areas Newly graded areas (pervious areas only, no vegetation) 5/
Idle lands (CNs are determined using cover types similar to those in the table titled ‘Runoff curve numbers for other agricultural lands’). For curve numbers for agricultural and range land uses, see the Appendix.
186 STORMWATER MANAGEMENT
and have clayey textures. The saturated hydraulic conductivity of group D is less than or equal to 0.40 micrometres per second (0.06 inches per hour) (USDA, 2007). TR-55 also introduces the run-off curve number, which is very similar to the coefﬁcient of run-off (C) in the rational calculation method discussed above. Table 9.2 provides the curve numbers for various types of land uses (cover descriptions) with one of the four hydrologic soil groups. See the Appendices for tables with curve numbers for additional land uses. We will return to consideration of hydrologic soil groups and curve numbers in the discussion of inﬁltration later in this chapter.
Stormwater quality improvement Stormwater contaminants While the treatment of domestic sewage concentrates on the reduction of total suspended solids (TSS), biological oxygen demand (BOD), total nitrogen, ammonia, nitrate, phosphorus, disease-causing bacteria and pharmaceuticals, stormwater often contains heavy metals, hydrocarbons, phenols and other toxins, some of which are known carcinogens. Typical concentrations of pollutants in urban stormwater are TSS – 54.5 mg/L, total phosphorus – 0.26 mg/L, total nitrogen – 2.0 mg/L, copper – 11.1 g/L, lead – 50.7 g/L, zinc – 129 g/L, faecal coliforms – 1.5 colony-forming units (CFU)/100 mL (Kadlec, 2009). However, these levels vary considerably depending on the type of land use that generates the stormwater. Some land uses contribute high concentrations of particular stormwater contaminants (Table 9.3). Most of the concentrations of nutrients, bacteria and metals from the highlighted land uses are far above the US Environmental Protection Agency (EPA) standards for surface water. All of the land uses listed in Table 9.3 contribute all the listed pollutants, but the table displays only pollutant concentrations for the land uses contributing the highest levels. This helps us select the type of treatment wetland best suited for the removal of the most problematic contaminants.
Table 9.3 Stormwater run-off pollution concentration and land uses making the greatest contributions of pollutants (Kadlec, 2009)
Contaminant Land use Lawns Commercial streets Auto recyclers Industrial parking Landscaping Residential streets Driveways Urban highways Rural highways Industrial roofs Heavy industrial land Water quality standard
E. coli CFU
602 468 335 228
TN mg/L 9.1
94,000 37,000 2.1 3 22 30
.55 .56 .32
62 148 13
43 290 65
1,390 1,600 120
Kadlec, 2009. CFU = colony-forming units per 100 mL; mg/L = milligrams per litre; g/L = micrograms/L; TSS = total suspended solids; E. coli = pathogenic bacteria; TN = total nitrogen; P = phosphorus.
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Species of pathogenic bacteria, in addition to E. coli, noted in Table 9.3, are also present in high concentrations in storm run-off. Faecal coliform, total coliform and E. coli bacteria are highly correlated with one another and with turbidity and suspended solids concentrations (Peters, 2009). Total nitrogen listed in Table 9.3 includes organic nitrogen, ammonium, nitrite and nitrate. While there are no water quality standards for total nitrogen, concentrations of 0.2 mg/L for nitrite and 1 mg/L for nitrate are generally accepted maximums (Li and Davies, 2009). The contaminants in urban and suburban stormwater accumulate on surfaces through atmospheric deposition during dry periods, through vehicle emissions from burning fossil fuel, through the wear and disintegration of tyres, brakes, engine and other components, through animal waste from pets, and through fertilizers, pesticides and other chemicals applied to the landscape, buildings and paving. However, diesel oil, concrete, asphalt, undercoating, exhaust and antifreeze contribute contaminates also. Rain run-off washes these contaminants into surface waters. The concentration of contaminants is especially high after periods with no rain and during the initial ﬂow from a storm. About the ﬁrst 25 per cent of run-off is particularly polluted and is called the ‘ﬁrst ﬂush’. Therefore, it is particularly important to capture this portion of run-off and remove as much of the pollution as possible.
Parking lot contaminants Table 9.4 shows the levels of metals, suspended solids and 25 types of polycyclic aromatic hydrocarbon (PAH) from parking lot run-off after simulated rain in a southern California city (Long Beach). PAHs are formed from burning coal, oil, gas and garbage, when combustion is incomplete. It also enters the environment through pavement-sealing coats made from coal tar (common in the eastern United States) (Mahler et al., 2012). Breathing PAH-polluted air or consuming contaminated water or food creates human health risks, including cancer. The compounds are long-lasting and most are insoluble in water. PAHs are associated with high levels of TSS in urban run-off. The California study revealed that a rainfall intensity of at least 0.24 inches per hour (6 mm/hour) is required to wash contaminants from the paving surface. The
Table 9.4 Levels of parking lot contaminants after a 28-day antecedent dry period. Long Beach, California (Tiefenthaler, Schiff and Bay, 2001)
Dissolved metals Aluminum (g/L) Cadmium (g/L) Chromium (g/L) Copper (g/L) Iron (g/L) Lead (g/L) Mercury (g/L) Nickel (g/L) Silver (g/L) Zinc (g/L)
131.7 (62) 1.3 (1.2) 2.3 (1.1) 28.5 (13.4) 286.7 (140.0) 22.8 (14.0) 0 (0) 16.2 (7.7) 0 (0) 131.7 (62)
Suspended solids (mg/L) 51.8 (14.1)
Total metals Aluminum (g/L) Cadmium (g/L) Chromium (g/L) Copper (g/L) Iron (g/L) Lead (g/L) Mercury (g/L) Nickel (g/L) Silver (g/L) Zinc (g/L) Total PAHs (g/L)
533.3 (119.2) 2.5 (1.4) 3.6 (0.5) 40.3 (7.2) 810.0 (174.4) 41.8 (10.6) 0 (0) 20.7 (2.4) 0 (0) 620.0 (60.4) 82.4 (33.7)
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concentration of contaminants increased approximately 600 per cent during a 28-day antecedent dry period, but was lower than this maximum after 2- and 3-month antecedent dry periods. All loose particles were washed from the paving surface during the ﬁrst 15 minutes of simulated rainfall. The highest concentration of pollutants was found in samples collected after the ﬁrst 10 minutes of light simulated rainfall (6 mm/hour). Higher intensity rainfall (13 and 25 mm/hour) diluted the concentration of pollutants (Tiefenthaler, Schiff and Bay, 2001). The toxicity of the stormwater run-off was characterized according to its impact on sea urchins (Strongylocentro purpura), ocean bacteria (Vibrio ﬁscheri) and mysids (Americamysis bahia, marine crustaceans). All stormwater samples, whether taken during the ﬁrst ﬂush or later in the storms, were toxic to these organisms. The ﬁrst ﬂush samples were twice as toxic as other samples. All three organisms died or were affected in reproduction or growth. The primary factors in this toxicity were heavy metals, particularly zinc. Street sweeping and the intensity of parking lot use did not signiﬁcantly change the contamination levels. Notice in Table 9.4 that the proportion of total metals which are in the dissolved state is high. This is of concern since this pollution form is more difﬁcult to remove from stormwater than metals in particulate form (Tiefenthaler et al., 2001).
Roadway contaminants Like parking areas, roads are particularly potent sources of pollutants. Annually, highway stormwater run-off at the concentration of 0.71–1.07 mg/L contributes 4.76–7.64 pounds per acre per year of nitrate to the adjacent landscape and receiving waters, while total phosphorus at the concentration of 0.10–0.33 mg/L generates 0.72–1.76 pounds per acre per year (Hunt, 2003). Table 9.5 shows data from a Texas study of highways with three levels of daily vehicle use (>50,000, >43,000, >35,000) and the pollutants that washed off the pavement surfaces during storms. This data helps us predict the concentration of pollutants that will require treatment. This data is conﬁrmed by other studies, but the values vary considerably according to continent and within continents. Higher
Table 9.5 Mean contaminant concentration for six roads in Texas, with an average daily traffic count of 35,000 to more than 50,000. Units mg/L (Li et al., 2008)
TSS mg/L 116 172 124 TKN mg/L 2.131 1.940 1.786 NO3+2 mg/L 0.37 1.064 0.897 Total phosphorus mg/L 0.217 0.238 0.216 Dissolved phosphorus mg/L 0.119 0.112 0.126 Total copper g/L 14 17 16 Dissolved copper g/L 6 6 6 Total lead g/L 7 9 6 Dissolved lead g/L Below detection limits Total zinc g/L 117 118 112 Dissolved zinc g/L 48 44 45 COD mg/L 73 71 92
118 1.130 0.434 0.132 0.040 27 6 13
124 1.510 0.340 0.130 0.050 22 6 10
173 1.760 0.220 0.280 0.090 30 5 14
167 57 64
140 49 81
175 50 100
TSS = total suspended solids; TKN = total Kjeldahl nitrogen; NO3+2 = nitrite and nitrate; COD = chemical oxygen demand.
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contaminant levels are reported for Europe and Asia than for the United States. There are strong correlations between TSS, total dissolved solids, total organic carbon and iron and 13 other constituents and parameters (turbidity, oil and grease, total petroleum hydrocarbons, total Kjeldahl nitrogen (TKN), electrical conductivity, chloride, cadmium, copper, chromium, nickel, lead and zinc). Therefore, TSS and the other three indicators can be used as general assessments of the presence and removal of the other 13 contaminants (Kayhanian et al., 2012).
General urban contaminants The negative impact on the ecosystem of stormwater from parking and roads is conﬁrmed by studies of general urban run-off where heavy metals, bacteria and excessive nutrients are present and contribute to the impairment of water bodies. For example, over 7,200 water bodies in California are deﬁned as impaired and about 1,200 of these are impaired due to excessive levels of bacterial pathogens (Kayhanian et al., 2012). Although it is diluted as it ﬂows into streams and rivers, the level of pollution in urban stormwater degrades streams and rivers. A study of the effects of urbanization on streams was conducted from 2003 to 2007 on watersheds with 69–93 per cent imperviousness. Twenty stream watersheds (Figure 9.9) near Atlanta, Georgia, were analyzed for a range of contaminants, including metals that are common in highway run-off. The ﬁrst 25 per cent of stormwater run-off from impervious surfaces (the ﬁrst ﬂush) resulted in high concentrations of copper, lead and zinc, but high levels sometimes occurred later in the storms. Copper and zinc in most of the streams exceeded Georgia’s chronic and acute standards (chronic levels damage aquatic organisms when exposure exceeds 4 days; acute levels damage aquatic organisms when exposure exceeds 1 hour). Lead was often detected at chronic levels. Copper, lead and zinc concentrations are highly correlated with each other and are present at high levels due to run-off from impervious surfaces (Peters, 2009).
Figure 9.9 The urban and suburban watersheds in the study of water quality in streams near Atlanta, Georgia. Photo: Google Earth, 33°44′44.83″ N 84°23′57.21″ W image date: 8 February 2013, image accessed: 7 June 2015.
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The Atlanta stream water quality study showed that faecal coliform bacteria levels exceeded the US EPA standard (200 most probable number (MPN)/L) for recreation uses in more than 90 per cent of the test samples taken from urban watershed streams. Faecal coliform, E. coli and total coliform bacteria were highly associated with suspended solids levels in the streams. Alkalinity, sodium, calcium, magnesium and potassium concentrations in the urban streams were four to ten times higher than in streams in more natural watersheds. This is probably due to the weathering of concrete. Generally, nutrient levels in the streams were high compared to streams in natural areas, but lower than EPA maximum standards for streams. For example, most of the urban streams had much less nitrate than 10 mg/L (EPA drinking water standard), and less than 10 per cent of the streams had more than 0.1 mg/L of phosphate (EPA limit causing algae blooms). High levels of chlorine were associated with combined storm and wastewater sewer outﬂow treated with sodium hypochlorite, as well as drainage from swimming pools and road de-icing salts (CaCl2) (Peters, 2009).
Contaminants from the ornamental landscape Insecticides, herbicides, pathogenic bacteria and fertilizers containing nitrogen and phosphorus are stormwater contaminants generated in large quantities by the ornamental landscape.
Phosphorus Phosphorus occurs naturally from the weathering of rock, but is present in the urban environment largely due its distribution as an artiﬁcial fertilizer. It is highly reactive, forming compounds with oxygen, iron, aluminium and calcium. Phosphate is the most common form and the simplest form of phosphate is orthophosphate (PO4) (phosphorus and 4 oxygen atoms). Phosphorus occurs in organic, inorganic, soluble and particulate forms. It is most available to plants and microorganisms in the soluble form. Phosphorus is added as fertilizer to turf to create about 25 mg/L of soil phosphorus for optimum growth. However, only 25 g/L (a quantity 1,000 times smaller) can promote excessive algae growth in lakes; 50–70 g/L of phosphors cause signiﬁcant and frequent algae blooms and the eutrophication of lakes. The decomposition of grass clippings and tree leaves from the ornamental landscape releases phosphorus. About 0.13 pounds of phosphorus (0.3 pounds P2O5) per 1,000 square feet is included in grass clippings during the growing season, and a tree canopy of 50 per cent coverage results in about 0.5 mg/L of phosphorus in street stormwater run-off (Spetzman, 2004). The target for phosphorus is 0.1 mg/L or less to avoid excessive algae growth, but many streams have this problem even at concentrations lower than this (US Environmental Protection Agency, 2010). The typical total phosphorus concentration in urban stormwater run-off in the United States is 0.26 mg/L.
Nitrogen Nitrogen is also a nutrient that causes growth of algae in aquatic systems, especially when phosphorus is also in excess (Figure 9.10). A survey of streams in the United States revealed that 40 per cent had high levels of phosphorus and 28 per cent had high levels of nitrogen. These excess nutrients contribute to aquatic conditions
STORMWATER MANAGEMENT 191 Figure 9.10 The rapid growth and subsequent death and decomposition of algae, as seen in this California urban stream, have devastating effects on the ecosystem, as this process depletes the oxygen in the water, causing damage or death to aquatic organisms. Photo: University of California, Davis. License: CC-BY-SA_2.0.
harmful to macro-invertebrates (US Environmental Protection Agency, 2013). Nitrogen enters aquatic systems through atmospheric deposition (as a product of burning fossil fuels), the decomposition of organic matter and the use of artiﬁcial fertilizer. In the urban environment, pet waste and treated sewage are signiﬁcant sources of excess nitrogen entering streams, rivers, lakes and oceans. The amount of nitrogen from fertilizer present in stormwater run-off varies according to the amount and type of fertilizer (quick or slow release), the soil inﬁltration rate, the slope of the land, storm intensity and density of vegetation. Streams not impacted by human activities have total nitrogen levels ranging from 0.12 to 2.2 mg/L (US Environmental Protection Agency, 2010). The typical total nitrogen concentration in urban stormwater run-off in the United States is 2.0 mg/L. Nitrate above approximately 5 mg/L causes algae blooms, loss of dissolved oxygen and eutrophication. The nitrate drinking water standard for adults is 10 mg/L. Ammonia (a form of nitrogen) is toxic to aquatic organisms, but toxicity varies by species, pH and temperature. However, the EPA acute (1 hour) criterion standard for freshwater is 17 mg total ammonia nitrogen/L and the chronic (30-day average) criterion is 1.9 mg/L (at pH of 7 and temperature of 20°C). These maximum levels are intended to protect sensitive species such as salmon and mussels (US Environmental Protection Agency, 2013).
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Nitrogen is present in the form of organic or inorganic compounds. The inorganic forms (ammonia and nitrate) of nitrogen are readily available to plants.
Stormwater treatment landscapes The overview of stormwater contaminants above reveals a great diversity in the pollutants generated by transportation, urban and suburban land use. High contaminant levels, coupled with the episodic nature of storms and run-off makes reducing the concentration and total amount of pollutants before they enter natural waterways a challenge. The conventional use of detention basins that temporarily store stormwater is ineffective for water quality improvement. Conventional wastewater treatment infrastructure similar to that used to treat municipal sewage could certainly improve the quality of stormwater, but the cost is prohibitive. Therefore, biological, landscape and multifunctional solutions have been sought. Many of these have been designed, constructed and monitored at the ﬁeld scale. They provide us with reliable models that we can adjust to respond to particular pollution problems, soil types, rainfall intensities, etc. Below, three treatment landscapes are presented with the information that planners, engineers and landscape architects require for master planning, sizing and construction detailing. The treatment performance of each system is also presented. The initial concentration of contaminants is presented for each case study, and this can be compared to the data in the tables above that characterize non-point source pollution from stormwater run-off. The treatment of pesticides and run-off from agricultural and industrial activities are presented in separate chapters. Pesticides used in the ornamental landscape are of the same classes as pesticides used in agriculture, and respond to similar treatment measures. This chapter concludes with a case study of the Qunli National Wetland Park to emphasize the multifunctional advantages and sustainable development potential of stormwater treatment landscapes.
JEL Wade Park case study Context Free water surface wetlands are the most common types of constructed wetlands for stormwater treatment. The JEL Wade wetland was designed and constructed to mitigate the impacts of non-point source pollution from suburban development on Hewletts Creek, a tidal creek, located in the city of Wilmington, North Carolina. Wilmington receives about 57 inches of rainfall per year. Figure 9.11 shows that the watershed is 19 per cent impervious due to the mix of urban and residential development. The wetland in JEL Wade Park has a 589-acre (238 hectares) catchment area. The size of the wetland (including the upland recreation area of the park) represents less than 1 per cent of its drainage area, but treats 47 per cent of its potential run-off. Historically, faecal coliform bacteria and excess nitrogen contaminated the creek causing algae blooms and the closure of shell ﬁshing areas nearby. The wetland (Figure 9.12) was designed to treat a 1-inch (2.5 cm) water quality storm, but it can contain and convey 100-year, 24-hour rainfall storms (Mallin et al., 2012).
STORMWATER MANAGEMENT 193 Figure 9.11 Approximately 20,200 people live in the watershed of the JEL Wade Park wetland. Photo: Google Earth © Google 2015 © TerraMetrics 2015. 34°10′39.96″ N 77°52′40.43″ W, image date: 3 January 2015, image accessed: 25 April 2015.
Figure 9.12 JEL Wade Park was constructed in 2007. It contains the 11.5-acre (4.7 hectare) wetland and 3.4 acres (1.4 hectare) of parkland. The area around the wetland includes park buildings, picnicking areas and a 0.75-mile (1.22 km) pedestrian loop trail including a boardwalk across the wetland (Li and Davies, 2009). Photo: Google Earth © Google 2015, © TerraMetrics 2015. 34°10′39.96″ N 77°52′40.43″ W, image date: 3 January 2013, image accessed: 25 April 2015.
Design The design of the JEL Wade free water surface wetland illustrates several recommended design elements. The stormwater enters the wetland at one end through two inlets, and ﬂows into two sedimentation basins. These are deep basins where the heaviest particles settle to the bottom. The sedimentation basin or forebay must be cleaned out after several years for continued water quality performance of the wetland. The 6-feet-deep, 30-feet-long sedimentation basins (item F, Figure 9.13) are graded to provide a relatively gentle vegetated entering slope for the ﬁrst two-thirds of their length. This encourages the growth of vegetation that slows and distributes stormwater, causing sediments to settle to the bottom of the basin. Capturing the sediment is beneﬁcial for extending the life of the wetland, easy excavation of the accumulated soil, and removal of heavy metals and disease-causing bacteria attached to the soil particles (especially small particles) (Mallin et al., 2012). Notched weirs at the outlet of each sedimentation basin evenly distribute the stormwater across the wetland width, while the water drops 6 inches (15 cm) into the wetland. Two of the weir notches contain ﬂash board risers that slow the ﬂow of water from the sedimentation basin. Two additional weirs that cross the wetland collect and redistribute water, as it drops in elevation at these low walls. The wetland contains two low-ﬂow streams that are fed by groundwater (Mallin et al., 2012).
194 STORMWATER MANAGEMENT
Figure 9.13 Plan view of the design for JEL Wade Park and wetland. A – play area; B – playground; C – restrooms; D – park building; E – vegetated area of sedimentation basin; F – sedimentation basin; G – weirs; H – low-flow streams; I – boardwalk and overlook; J – wetland with emergent and submerged marsh vegetation; K – outlet structure; L – by-pass channel; M – existing trees; N – shoreline vegetation. Image: Gary Austin based on design by Stewart Engineering.
Healthy, dense vegetation is a critical feature of a stormwater wetland. In the Wilmington case, the groundwater is high enough that it provides sufﬁcient water to sustain healthy wetland vegetation during the dry periods. The wetland and the sedimentation areas are dominated by cattail (Typha latifolia), Eastern bureed (Sparganium americanum), pickerelweed (Pontederia cordata), soft rush (Juncus effusus), giant cutgrass (Zizaniopsis miliacea), alligatorweed (Alternanthera philoxeroides) and parrot feather (Myriophyllum aquaticum) (Mallin et al., 2012). The complete plant list for the wetland is available in the Appendices. The water quality storm ﬂow is shallow and moves slowly through the wetland to receive maximum contact with the stems of the wetland plants and bottom sediment. The microorganisms and bacteria growing on the plants, sediment and decaying vegetation establish an ecosystem that utilizes the organic material, ammonium, nitrate, phosphorus and even complex and toxic organic compounds, such as petroleum hydrocarbons (Mallin et al., 2012). Treatment wetlands should be constructed with a ﬂat or minimal slope (0.5–1 per cent), and the JEL Wade wetland maintains the level areas by dropping elevation at the weirs (Figure 9.14). Water ﬂowing through the wetlands commonly seeks preferential routes across the wetland, which decreases the treatment effectiveness. Therefore, redistribution of the water at weirs and a roughly circular or square shape for the wetland, rather than long and narrow, are recommended. Both of these features are present in the Wilmington example. The water depth should vary from 6 to 18 inches deep for the water quality storm. In the Wilmington example, the sinuous route of the low ﬂow channels extends the length of the ﬂow pathway through the wetland and crosses the storm ﬂow to encourage distributed ﬂow through the vegetation.
STORMWATER MANAGEMENT 195 Figure 9.14 The JEL Wade wetland sedimentation basin and its outlet weirs are shown in the foreground of this image. The outlet is the concrete structure in the background. Photo: City of Wilmington, NC: reproduced with permission.
Sometimes deeper (4 feet) trenches are placed across the ﬂow path to encourage mixing and redistribution of water, and to provide cooler water for ﬁsh habitat. There is a small pool adjacent to the concrete outlet structure of the JEL Wade wetland, where a discharge pipe and overﬂow weirs control the normal depth of water in the wetland and the depth for storms greater than the water quality storm. The entire wetland is contained by a berm that prevents stormwater from ﬂowing into the basin except at the inlet, and contains the 100-year storm (Mallin et al., 2012).
Water management Although the JEL Wade wetland is intended primarily for water quality improvement, the basin has a positive effect on the peak run-off rate and time, and permanently stores a portion of each storm. Eight storms consistent with the magnitude of the water quality storm, ranging from 0.4 to 1.4 inches (1 cm to 3.5 cm), were monitored for 6-hour durations. The data shows that the wetland dramatically reduced both the rate and volume of the stormwater run-off from these storms. The wetland retained 50.3–74.5 per cent (63 per cent average) of the storm inﬂow. This is signiﬁcant since the volume retained in the wetland receives water quality treatment until it is removed by the subsequent storm, base ﬂow, inﬁltration or evapotranspiration. The average inﬂow of 15,185 cubic feet (430 m3) per hour was reduced by the wetland to an outﬂow average of 4,944 cubic feet (140 m3) per hour (Mallin et al., 2012).
Water treatment The primary water quality deﬁcit in the stormwater was pathogenic bacteria. Historically, high pathogenic bacteria levels caused the closure of shellﬁsh harvesting in the downstream tidal reach of Hewletts Creek. Stormwater inﬂow greatly exceeded the North Carolina standard for human contact for faecal coliform (200 CFU/100 mL), but the average level in the outﬂow, after treatment in the wetland, was well below this standard (Table 9.6). The stormwater wetland decreased an average of 99
196 STORMWATER MANAGEMENT Table 9.6 Pollutant mean concentrations entering and exiting the wetland (Mallin et al., 2012)
Inflow 1 reduction %
Inflow 2 reduction %
Total suspended solids, mg/L 9.8 ± 10.5
15.2 ± 7.2
4.1 ± 1.2
143 ± 65
43 ± 32
123 ± 42
159 ± 39
TKN, g/L g L
Total nitrogen, g/L
1,210 ± 1109
871 ± 374
529 ± 114
20 ± 21
93 ± 25
Total phosphorus g/L
59 ± 44
150 ± 53
43 ± 41
14.12 ± 7.562
44.12 ± 11.000
11.0 ± 6.80
‡ CFU, colony-forming units; CFU per 100 mL, geometric mean. Eight sampling events. TKN: Total Kjeldahl nitrogen (organic nitrogen and ammonia). ± standard deviation; g/L = micrograms per litre.
per cent of the faecal coliform bacteria. The average concentration of coliform bacteria in the wetland outﬂow was 42 CFU/100 mL. Removal of coliform bacteria in the wetland was highest when the inﬂow concentration was also high and during the warmest weather. The warm weather effect is probably due to increased predation of bacteria by microorganisms (Mallin et al., 2012). Removal of bacteria pathogens in free water surface and other wetland types is highly dependent on residence time and internal ﬂow patterns. Rotifers and protozoa are microorganisms that prey on bacteria. Rotifers are abundant in the outﬂow of treatment wetlands. They are commonly about 10 rotifers in each millilitre of water in a treatment wetland. At this concentration, rotifers can disinfect stormwater detained for 1.2 hours in a marsh wetland (Kadlec, 2009). The TSS concentrations ﬂowing into the wetland were generally low. However, when the TSS concentrations were highest in the inﬂow, the wetland removed 98.8 per cent of them. The Wilmington wetland was quite effective in the removal of ammonium and nitrate, which is important for the improvement of the shellﬁsh area downstream. The wetland removed more that 90 per cent of the ammonium and orthophosphate, and 89 per cent of the total phosphorus. Nitrate removal was very high, especially in the warmer months. Nitrate removal was 68–83 per cent when water temperatures were less than 53.6°F (12°C), but 90–97 per cent when the water temperature exceeded 59°F (15°C) (Mallin et al., 2012). In the case of the JEL Wade wetland, it was important to remove nitrate from the stormwater, as it sustains pathogenic bacteria and causes algae blooms, which could compromise the shellﬁshery downstream. Total nitrogen removal ranged from 66 to 96 per cent. Heavy metals concentrations in the inﬂow were low with the
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occasional exception of zinc. The level of zinc in the outﬂow was always well below the state standard (Mallin et al., 2012). The performance of the JEL Wade wetland is conﬁrmed by comparison to the Dye Branch wetlands located in Mooresville, North Carolina. This wetland watershed is 60 per cent impervious with a run-off curve number of 87.5. Completed in 2006, this 0.81-acre stormwater wetland is composed of three treatment cells. The removal of contaminants is even better than in the JEL Wade wetland, with the exception of phosphorus, although this was still a very high removal percentage: TSS – 88 per cent, total phosphorus – 67 per cent, total nitrogen – 58 per cent, organic nitrogen – 36 per cent, total ammonia – 90 per cent, TKN – 48 per cent, nitrite and nitrate – 85 per cent. The removal of organic nitrogen is fairly low. This is probably because free water wetlands simultaneously remove and add organic nitrogen to the water, so it may not be possible to improve this signiﬁcantly unless a different type of wetland is added to the treatment sequence (Hathaway and Hunt, 2009). In fact, there was only a small improvement in the quality of the water after the second treatment cell. A different kind of wetland, such as a horizontal subsurface ﬂow cell, might have made more signiﬁcant improvement in some parameters. Other examples of stormwater treatment wetlands show performance much lower than in the JEL Wade and Dye Branch examples. This points to the need for careful evaluation of site conditions, target contaminants and good design.
Other benefits of the JEL Wade wetland The example of JEL Wade Park shows the multifunctional character of stormwater wetlands for water quality improvement, open space, recreation and habitat. Although the park is primarily dedicated to stormwater capture and treatment, there are several additional uses. A mundane one is the electrical transmission line corridor that shares the space. There are also public amenities including a restroom, a park building, playgrounds, turf play areas, a pedestrian/bicycle trail, a boardwalk and even educational panels (Figure 9.13). In addition, the preservation of many groves of existing trees and the planting of many other trees, shrubs and wetland vegetation generate ecosystem and aesthetic beneﬁts. Urban biological diversity is enhanced due to the size of the park and types of vegetation planted. There is a wide range of ecosystem elements and recreation and educational amenities that are normally expensive for the city to provide. The combination of the water management, treatment and these other ecosystem and human beneﬁts reduces the cost of providing them, compared to creating parks dedicated to each category (Mallin et al., 2012).
Off-line stormwater treatment wetlands The JEL Wade stormwater wetland combines the stormwater management and treatment functions into a single facility. However, this may not be the optimal design, as during storms larger than the water quality storm, it can result in scouring of the wetland soil, high water velocity, and deep and lengthy inundation of the vegetation. Instead, parallel basins provide a better opportunity to control the treatment landscape that is independent of the stormwater management function. Figure 9.15b illustrates a design where the water quality storm volume is routed to the treatment cells, while the larger volume of more intense storms is routed to a pond for detention.
198 STORMWATER MANAGEMENT Figure 9.15a Plan view of stormwater management and treatment cells that operate in parallel. In the plan, the sedimentation basin is at the upper left. Water flows to the large stormwater management basin. A reverse flow pipe delivers the water quality storm to the first treatment basin (lower left). Image: Austin adapted from Virginia Department of Environmental Quality (2013).
Figure 9.15b Perspective view of stormwater management and treatment cells. In the perspective, the sedimentation basin is at the lower left and the treatment basins are at the top. Since only the water quality volume enters the treatment cells, the vegetation is protected from excessive inundation depth, duration and other negative impacts of managing large storms. The first treatment basin contains deep and shallow marsh sections. Image: Austin adapted from Virginia Department of Environmental Quality (2013).
The sedimentation basin (holding 15 per cent of the water quality storm) serves the treatment cells and an extended detention basin, which is sized to contain the 10- or 25-year storm as required by local ordinances. The extended detention basin water level might ﬂuctuate several feet, while the inundation level in the treatment cells is limited to 12 inches above the normal water level. A reverse slope pipe from the extended detention pond controls the water levels within the treatment cells (Figure 9.15b). A volume of water equal to one half of the water quality storm is permanently retained in the extended detention basin and is correctly assumed to be part of the water quality treatment system. Ideally the extended detention basin is well vegetated with plants tolerant of deep water and deep inundation, such as cattail or common reed. The limited inundation depths within the treatment cells better preserves abundance and diversity of plants. The treatment wetland is designed to hold at least one water quality storm volume below the normal water level and one above it during storm events (Virginia Department of Environmental Quality, 2013). The treatment cells can be graded to include benches with water depths consistent with deep, normal and shallow marsh plant groups as well as ephemeral wet meadows or other zones, such as habitat mud ﬂats.
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Horizontal flow stormwater treatment basin The treatment landscape presented here combines features of the free water surface and the horizontal subsurface ﬂow wetland types. This design was created, constructed and tested by the University of New Hampshire, Stormwater Center, USA. It treats a 1-inch water quality storm (3,300 cubic feet) from a 1-acre parking lot (Roseen, Ballestero and Houle, 2009).
Pretreatment The water from the parking lot is discharged by a pipe into a sedimentation basin that contains 10 per cent of the water quality storm (Figure 9.18). This basin could be preceded or replaced by a bio-swale or other technique to remove particulates before water enters the treatment cells. All berms and basin edges have maximum slopes of 3h:1v (33 per cent) for safety and ease of maintenance. The accumulated sediment should be removed when 12 inches has been deposited (about every 4 years), and vegetation should be harvested annually (Roseen, Ballestero and Houle, 2009).
Treatment basins The treatment basins are rectangular and each is sized to contain 45 per cent of the water quality storm (Figure 9.16). The basins were excavated and then backﬁlled with ﬁlter media and a wetland soil layer. The minimum width of the basins is 15 feet (4.6 m) and the length to width ratio is 0.5 or greater (Figure 9.17). From top to bottom, the basins include a 6-inch freeboard, temporary pool, 8-inch thick (20 cm) wetland soil layer, 3-inch thick (8 cm) gravel transition layer and 24-inch deep (0.6 m) gravel ﬁlter layer. The top and bottom surfaces of the basins are level (Figure 9.20) (Roseen, Ballestero and Houle, 2009).
Flow sequence Water enters the sedimentation basin where it loses velocity before it overﬂows into the ﬁrst stage of the treatment wetland (Figure 9.17). The stormwater ﬂoods the surface of the ﬁrst basin. The sedimentation basin and temporary pools of the basins are aerobic treatment zones. The temporary pool drains into the gravel ﬁlter on the upstream end, through vertical perforated pipes (Figure 9.19). The central pipe is 12 inches in
Figure 9.16 This perspective of the subsurface flow gravel wetland shows two treatment cells in series. A sedimentation basin (Figure 9.17) discharge is on the left, in red. Image by Austin based on design by the University of New Hampshire Stormwater Center. Image: Gary Austin, 2016.
200 STORMWATER MANAGEMENT Figure 9.17 The three-basin subsurface gravel wetland at the University of New Hampshire. The sedimentation basin is in the background. The top of the basin is much higher than the intermediate berms due to its location on a slope below the parking lot. Note that the three vertical pipes on the upstream side of the treatment cells distribute water to the subsurface gravel filter. Photo: Tom Ballestero, UNH Stormwater Center: reproduced with permission.
Figure 9.18 The sedimentation basin of the subsurface gravel wetland at the University of New Hampshire supports dense wetland vegetation 4 years after planting. The inlet into the first treatment cell is on the right. Photo: Tom Ballestero, UNH Stormwater Center: reproduced with permission.
diameter; all others are 6-inch diameter perforated PVC pipes (Roseen, Ballestero and Houle, 2009). These vertical drains are spaced 15 feet apart and connect to a horizontal 6-inch diameter perforated PVC pipe that distributes the stormwater evenly across the width of the wetland (Figure 9.19). Water ﬂows horizontally (15 feet, 4.6 m, minimum) and slowly through the gravel ﬁlter. This is the anoxic (oxygen limited) treatment zone. At the downstream end of the gravel bed of the ﬁrst treatment basin, the water is collected by another horizontal 6-inch diameter perforated PVC pipe (at least 15 feet, 4.6 m, away). This is connected to a horizontal, solid, 6-inch PVC pipe that delivers the water to the next treatment basin. The piping in the second basin is the same as in the ﬁrst stage, until the water drains into the outlet structure. Solid vertical PVC clean-out pipes are connected to the ends of the horizontal collection pipes (Roseen, Ballestero and Houle, 2009).
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Figure 9.19 This schematic perspective of the piping system for the gravel wetland shows the sequence from the sedimentation basin on the left. The red colour indicates inlet and overflow pipes, green indicates perforated pipes, yellow shows the solid clean-out and transfer pipes, and the violet is the outlet structure. Notice the elevated yellow pipe exiting the outlet structure. It maintains the permanent saturation of the gravel bed. Image: Gary Austin.
The outlet elevation is set at 4 inches below the surface of the wetland soil layer (Figure 9.20). This assures that a volume of water is held in the basin after the storm ends, and provides anoxic or anaerobic conditions for the removal of nitrates (denitriﬁcation) (Roseen, Ballestero and Houle, 2009). When the inﬂow is high enough, the ﬁrst temporary pool overﬂows into the second treatment basin. Although the University of New Hampshire gravel wetland contains only the water quality storm. The basin can be designed to detain and covey the storms larger than the water quality storm by increasing the height of the berms and adding weirs to the outlet structure as required by local stormwater ordinances (Roseen, Ballestero and Houle, 2009).
Wetland and subgrade soil The native subsoil below the ﬁlter bed should have a hydraulic conductivity less than 0.03 feet per day (0.9 cm per day). If it does not, then a 6–12 inch (15–30 cm) layer of clay soil, a layer of bentonite or a 30 ml high density polyethylene liner should be used to prevent inﬁltration (Roseen, Ballestero and Houle, 2009).
Figure 9.20 This is a section through the gravel wetland. From top to bottom, the layers are: the temporary pool, the 8-inch deep wetland soil, the pea gravel transition layer, the gravel filter bed, the impermeable liner and the compacted native soil. The water is maintained at the centre of the wetland soil layer. Image: Gary Austin.
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Materials The berms of the sedimentation basin and the treatment basins should have a low inﬁltration rate or be composed of clay or a ﬁne mesh geotextile fabric, or a combination of these (Roseen, Ballestero and Houle, 2009). The wetland soil can be created from loam and 15 per cent mulch, such as shredded wood, and less than 15 per cent clay and silt. The resulting soil should have a saturated hydraulic conductivity of 0.1–0.01 feet per day (3.05–0.305 cm/day) (Roseen, Ballestero and Houle, 2009). The transition gravel layer should be 1⁄4 inch in diameter (pea gravel) to prevent migration of silt and clay into the gravel ﬁlter. A thin layer of coarse sand could be added above this transition layer, if desired, to further guard against migration of clay and silt into the ﬁlter media. Geotextile fabric should not be substituted for the gravel transition layer. The gravel ﬁlter bed should be composed of graded and washed gravel 3 ⁄4 inch (2 cm) in diameter. Spillways and swales and pools receiving water from pipes should be covered in gravel 11⁄2–3 inches (4–8 cm) in diameter, to dissipate energy and prevent erosion. The plants should be native species. The sedimentation basin may hold enough water to support emergent macrophytes, such as cattail (USA) (Figure 9.18) or
Figure 9.21 This image is of a subsurface gravel wetland at Greenland, New Hampshire, that is based on the design developed at the University of New Hampshire Stormwater Center. The receiving stream is degraded with high levels of TSS – 53 mg/L, total nitrogen – 1.35 mg/L and total phosphorus – 0.145 mg/L. Water discharged from the gravel wetland has a much lower concentration of pollutants than stream (TSS – 3 mg/L, total nitrogen – 0.50 mg/L, total phosphorus – 0.005 mg/L). Photo: Robert Roseen, UNH Stormwater Center: reproduced with permission.
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common reed (Europe and Asia). However, wet meadow plants are more likely to thrive in the treatment basin (Roseen, Ballestero and Houle, 2009) as shown in Figure 9.21. An application of the University of New Hampshire design to a shopping centre project shows meadow vegetation in the treatment basin (Figure 9.21).
Outlet structure The outlet structure can be designed in various ways to comply with local ordinances. These might require that the 25-year, 24-hour storm be detained and released at predevelopment rates, for example. Similarly, the oriﬁce that controls the release of the water treated in the gravel bed should be sized to conform to local codes that often require that the temporary pool be drained within 24–48 hours. This prepares the basin to receive inﬂow from subsequent storms. The invert (outlet elevation) of the outﬂow pipe should be set 4 inches (10 cm) below the top of the wetland soil to maintain a saturated gravel bed and make water available between storms to the wetland plants (Roseen, Ballestero and Houle, 2009). An adjustable riser on the outlet pipe is recommended to allow adjustment of the water level within the wetland. This is valuable during plant establishment and subsequent maintenance. A secondary discharge drain, that is normally closed, is an optional but valuable addition to the system. This allows rapid draining of the wetland and gravel bed for maintenance and allows the system to be ﬂushed at a higher water velocity.
Treatment performance The University of New Hampshire subsurface gravel wetland has been monitored for a number of years to assess its stormwater management, treatment performance, maintenance requirements and longevity. It has proved to be highly effective and reliable. Therefore, the design is being increasingly installed in both the private and public sectors.
Stormwater management The stormwater peak ﬂow from the New Hampshire wetland was greatly reduced and the time of the peak ﬂow was greatly delayed. Both of these characteristics are signiﬁcant beneﬁts to the receiving streams within urbanizing watersheds. The peak ﬂow was reduced by an annual average of 81 per cent (85 per cent in the winter and 77 per cent in the summer). The time of the peak ﬂow was delayed 315 minutes on average.
Stormwater quality improvement Each treatment basin of the subsurface gravel wetland ﬁlters the entire water quality storm volume for small frequent storms. The water treatment for water quality improvement is effective because this design takes advantage of sedimentation and sequestration, physical ﬁltration, biological transformation, plant uptake and even chemical process that bind pollutants to soil. Hydrocarbons, heavy metals and bacteria in the polluted inﬂow are captured in the sedimentation basin and the wetland pools. Organic material captured in these locations also decomposes to create ammonia and
204 STORMWATER MANAGEMENT Table 9.7 Horizontal subsurface flow gravel wetland pollution removal performance (from parking lot catchment area), 6 years of data
Total petroleum hydrocarbon mg/L Total nitrogen mg/L Ammonia, nitrite and nitrate mg/L TSS mg/L Total zinc mg/L Total phosphorus mg/L Ortho phosphorus mg/L
644.0 1.1 0.3 57 0.04 0.07 0.02
6.44 0.44 0.075 1.14 0.007 0.031 0.005
99% 56% 75% 98% 83% 56% 75%
Robert Roseen; Thomas Ballestero; James Houle; University of New Hampshire Stormwater Center.
nitrate as this is an oxygen-rich environment. The removal of nitrates depends on the oxygen-limited environment provided in the subsurface gravel ﬁltration bed. This combination of pollution reduction pathways results in outstanding water quality (Table 9.7). The average annual reduction in the concentration of nitrate in the subsurface gravel wetland is more than 75 per cent (33 per cent in the winter and 85 per cent in the summer) with an average concentration of less than 0.05 mg/L (Roseen et al., 2012). This is a fraction of the 5 mg/L that can cause algae blooms. The average annual total nitrogen removal is good at 58 per cent. The removal of TSS and petroleum hydrocarbons is excellent. Phosphorus removal is moderate (56 per cent) and might be improved through the use of gravel with higher calcium content. Nevertheless, the 0.031 mg/L concentration of total phosphorus in the outﬂow is below the 0.1 mg/L target for protection of streams and lakes. The vegetation within the treatment basins should be harvested at least every 3 years for best treatment performance (Roseen, Ballestero and Houle, 2009).
Retrofit Conventional stormwater detention basins have little water quality beneﬁt. However, they can be modiﬁed to perform both their intended stormwater management functions while incorporating all of the elements of the New Hampshire subsurface gravel wetland described above for greatly improved treatment performance. Since the subsurface gravel wetland is intended to have no bottom slope, and no separation from ground water is required, the system is easily adapted to conventional detention settings. The hydraulic pressure requirement for the gravel wetland is only 4 inches (10 cm) (Roseen, Ballestero and Houle, 2009). Converting detention basins to subsurface gravel wetland is a low cost manner for municipalities to upgrade their infrastructure and meet more stringent water quality requirements and restore polluted streams and lakes.
Conclusion This installation of a subsurface gravel wetland focused on the technology, construction speciﬁcations and testing of the system performance for water management and treatment only. However, as these systems are incorporated into the public landscape,
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additional design considerations are necessary to improve their appearance and their contribution for wildlife habitat. Municipal master planning to incorporate the wetlands into a green infrastructure network, good planting design and integration of user facilities will make the basins positive contributors to the open space networks as well as essential tools for sustainable development.
Bio-retention basins for stormwater treatment Stormwater treatment wetlands, such as the marsh landscape and the subsurface gravel wetland, presented above, are suited to the scale of the neighbourhood or large parcel, but smaller stormwater treatment landscapes are needed for the scale of residential or commercial sites. In this setting, the emphasis on aesthetics often increases. The bio-retention basin is a treatment landscape based on design and experience with vertical subsurface ﬂow constructed wetlands developed to treat domestic sewage. However, the design is adapted to treat non-point source pollution with a fraction of the organic nitrogen content, intermittent stormwater ﬂow and with a different ﬁlter media capable of supporting plants more common to the forest and ornamental landscape. Rain gardens are similar to bio-retention basins. Rain gardens are simply shallow depressions in the ornamental landscape intended to hold 6 inches or less of stormwater from roof downspouts or other impervious surfaces. They are planted with water-tolerant trees, shrubs and herbs. Rain gardens are valuable low impact development measures that address stormwater volume, run-off rate and treatment. Bio-retention basins are more robust versions of rain gardens, sharing the set of appropriate plants and small-scale application. However, the bio-retention basin is engineered to improve the quality of stormwater. Like the vertical subsurface ﬂow constructed wetlands, bio-retention beds are intended to dry (and renew their oxygen content) between storms (Figure 9.22). Filtration, chemical and biological processes all contribute to the removal of contaminants in the stormwater. This full set of treatment processes makes the bio-retention basin much more effective in the removal of contaminants than detention or retention (wet pond) stormwater basins. In fact, typical stormwater basins have little, or even a negative, water quality improvement beneﬁt (Davies, 2001; Mallin, 2002; Hathaway, 2009).
Figure 9.22 Bio-retention basin at Tabor School in Portland, Oregon. Photo: Gary Austin, 2012.
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Design criteria Government design standards for bio-retention basins are either unavailable or outdated in most states. Initially, guidelines were established based on very little research data and a limited set of goals. Monitoring of installed bio-retention basins over the last 10 years provides more reliable criteria, installation and performance expectations.
Pretreatment When bio-retention basins fail to perform as intended, it is most often due to construction errors and clogging of the ﬁlter media. Therefore, a sedimentation basin, bioswale or tank is recommended to remove as much sediment and suspended organic material as possible, before it can enter the treatment basin. When a sedimentation basin is used, it should be sized to contain 25 per cent of the water quality storm volume. A wide grass ﬁlter strip, upstream of the bio-retention basin, was initially required by the regulations of some government agencies. This transition area was intended for sheet ﬂow of stormwater to capture sediment and was related to the single circumstance of bio-retention basins along roads. This technique is effective, but it is only one alternative for capturing sediment and TSS.
Treatment basin The relationship between the drainage area and the area of the bio-retention basins is typically 5–8 per cent of the catchment area (sometimes this is limited to the size of the impervious area of the catchment), but the size varies with the stormwater strength and water quality goals set for the basin. Suggested maximum widths for bio-retention basins (25 feet) are based on the ability to excavate the basin with heavy equipment located outside the basin, to avoid compaction of the bottom soil. However, this does not apply to bio-retention basins, where inﬁltration of the treated stormwater is not desired. Even where inﬁltration is a goal, the basin width could be expanded with post-excavation measures such as ripping the soil, installing boreholes or inﬁltration trenches. A bucket with teeth should excavate the ﬁnal 12 inches of a basin intended for inﬁltration, in order to limit compaction of the basin bottom. Research shows that inﬁltration into loamy sand subsoil is 2.6 inches per hour when the basin is dug with a rake bucket, as compared to 1.2 inches per hour for a basin dug with a ﬂat-edged bucket. This translates into a basin drawdown of 12 hours and 27 hours for the rake and ﬂat edge bucket, respectively. Similarly, inﬁltration will be higher if the basin is dry when dug (Brown, 2010). The basin includes a portion above the soil surface to temporarily contain a pool equal to 75 per cent of the water quality storm volume (Figure 9.23). The maximum depth of ponding is a matter of some debate. Most states with regulations set the maximum surface pond depth between 6 and 18 inches. If the ﬁlter media and subsoil have a high inﬁltration rate or the basin has an under-drain, the deeper surface pond is more acceptable. The depth of the surface pond should drop at about 1 inch per hour due to inﬁltration or outﬂow to draw down the temporary pool in several hours and the entire basin in 24–48 hours. A 6- to 12-inch freeboard above the maximum water level is a necessary safety factor. The surface of the basin should be covered with 3–4 inches of wood chips or
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Figure 9.23 Bio-retention basin preceded by a vegetated swale to reduce sediment and heavy metals and delay the storm peak. A – Earth berm with spillway or piped overflow; B – 6–18-inch ponding depth; C – 4-inch wood chip mulch; D – Vegetated swale; E – Weir to retain water in swale. Image: Gary Austin, 2016.
other mulch. This appears to be particularly important if hydrocarbons are targeted for removal, as bacteria in mulch rapidly decompose absorbed hydrocarbons, such as toluene and naphthalene (Davis et al., 2009). The basin should be deep enough to contain 24–48 inches of sandy ﬁlter media. Underneath the ﬁlter media, a 6–16 inch depth of sand or gravel is sometimes speciﬁed to improve inﬁltration. However, this is probably not beneﬁcial for a correctly designed and constructed basin. Metals and suspended solids are reduced signiﬁcantly in the top 8 inches (20 cm) of the media, which is where much of the pathogenic bacteria are also removed. However, removal of hydrocarbons, total nitrogen and phosphorus seems to beneﬁt by depths of at least 30 inches (Davis et al., 2009). When the subsoil has an inﬁltration rate below 0.5 inches per hour, an underdrain in a bed of coarse gravel (1–2-inch diameter) is recommended (Figure 9.24). As a transition layer to prevent the migration of ﬁne soil particles, the coarse gravel should be separated from the ﬁlter media by a 2–4-inch gravel layer of 1⁄4-inch diameter (pea gravel). Some installations even include a coarse sand transition between the ﬁlter media and the pea gravel (University of New Hampshire, 2007).
Flow sequence Stormwater from impervious surfaces or the ornamental landscape is directed through bioswales, a sedimentation basin or other pretreatment before ﬂooding the treatment basin. The water drains vertically through the sandy ﬁlter media and into the subsoil or into under-drains. Under-drains are used when the inﬁltration rate of the native soil is less than 0.5 inches per hour or when the groundwater is seasonally within 3 feet of the bio-retention basin bottom. When there is limited inﬁltration, perforated PVC under-drains in a coarse gravel drainage layer discharge the treated stormwater to the surface waters (Figure 9.24).
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Figure 9.24 Underground view of a bio-retention basin with a flooded sub-basin (internal water storage). Total depth is about 4 feet. A – Sandy loam filter (80 per cent sand, less than 3 per cent silt and clay); B – 2 inch depth of 1⁄4-inch diameter gravel transition; C – 3-inch depth of 3⁄4-inch diameter gravel transition; D – 11⁄2-inch diameter gravel sub-basin; E – Perforated drain pipes connected to a turned up discharge line. Image: Gary Austin, 2016.
When reduction of nitrate is an important goal, then a permanently saturated 24inch-deep layer of gravel is included below the main ﬁlter media. This creates an anaerobic zone that encourages the growth of bacteria that use carbon instead of oxygen as an energy source. In the process, nitrate is converted to harmless nitrogen gas that escapes to the atmosphere. In Figure 9.24, the elevated discharge pipe, E, will cause water to be retained in the gravel beds, C and D. Inﬂow from the subsequent storm causes the retained water to be discharged. Therefore, a volume of water is held, after the storm ends, for longer treatment. Within about 1 hour, oxygen in the retained water will be depleted by microorganisms, creating anaerobic conditions that are suitable for denitriﬁcation by bacteria. This is the ﬁnal step in a complex sequence including organic matter > ammoniﬁcation > nitrite > nitrate > denitriﬁcation > nitrogen gas.
Subgrade soil Inﬁltration of water treated in a bio-retention basin may be desirable for groundwater recharge, to maintain base ﬂow in the soil or to reduce stormwater run-off volumes. Where groundwater recharge is implemented, high water quality should be achieved before inﬁltration. Nitrates are poorly removed from bio-retention basins constructed without a water impoundment below the media. Nitrates are also not held in the soil and, therefore, are likely to drain into groundwater especially if it is within a few feet of the surface. Therefore, agricultural drainage areas, brownﬁelds or current industrial
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land are poor locations for bio-retention basins with inﬁltration due to elevated levels of nitrates or toxic chemicals. If inﬁltration is desired, then the character of the soil below the bio-retention basin is important. Generally, a subsoil inﬁltration rate of 0.5 inches per hour is required to drain the saturated basin. The saturated hydraulic conductivity of loam is 0.52 inches per hour, while for silty loam and sandy loam it is 0.27 inches per hour and 1.2 inches per hour, respectively. Hydraulic soil groups A and B, as deﬁned by the US Natural Resources Conservation Service, are most suitable, but silty loam soil (type C) might be suitable under certain design conditions. A silty loam soil below 13 inches of ponded water in a bio-retention basin will be eliminated in 48 hours, while in a loam soil this takes only 24 hours. A sandy loam soil will draw down 24 inches of ponded water in 24 hours. It is important to reduce the standing water in the bioretention basin steadily so that capacity is available for storms occurring at short intervals. However, an excessive inﬁltration rate of more than 3 inches per hour is not desirable, as this reduces treatment time and also indicates a soil unsuitable for most plants. If 0.5–1 inches of water from every storm is inﬁltrated to recharge groundwater, this typically meets or exceeds preconstruction inﬁltration rates (Davis et al., 2009).
Materials Filter media Originally the bio-retention basin was planted with a mix of shrubs, ground cover and trees to resemble a native forest. Concern that using coarse sand or gravel, as in a vertical subsurface ﬂow wetland, would be too infertile and dry too quickly, led to initial speciﬁcations for loam soil. This caused the bio-retention basins to clog quickly, as did the use of ﬁlter fabrics to separate the media layers in the basin (University of New Hampshire, 2007). Most speciﬁcations today require 80–88 per cent sand for the main ﬁlter layer. Small amounts of shredded bark, mulch and loam soil are generally speciﬁed, but ﬁnes (silt and clay) are limited to 7 per cent. However, an effective bioretention basin with a sandy clay loam soil (54 per cent sand, 26 per cent silt, 20 per cent clay) and 12.2 per cent of organic matter performed better in removal of most pollutants than a basin with sandy loam soil (80 per cent sand, 13 per cent silt, 7 per cent clay, 5.7 per cent organic matter). In this study, performance testing over 14 months began only 1 month after the basin was completed, so the long-term inﬁltration rate is not known. Compost should be used with caution, as it is likely to increase the amount of nitrogen and phosphorus in the efﬂuent. Where organic matter, ammonium or nitrates are in high concentrations, such as in agricultural run-off, solid carbon (wood chips) in a horizontal subsurface ﬂow bed has proven to be very effective for removal of nitrates from agricultural run-off (Schipper et al., 2010). A laboratory study demonstrated an 87 per cent reduction of nitrate when carbon was added to the media of a saturated bioﬁlter (Yang, 2010). This is a topic requiring additional research. Speciﬁcations should require that all gravel be triple washed and media with a low phosphorus index be used. A bio-retention basin at Villanova University in Pennsylvania has been in operation for 7 years with no reduction in the inﬁltration rate. Its ﬁlter media is composed of 50 per cent sand and 50 per cent existing (well drained) site soil (Council, 2009).
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Plants The high sand content of the ﬁlter media necessary to maintain porosity of the ﬁlter bed creates a fairly difﬁcult growing environment for plants. However, there are ecosystems where sandy soils and high rainfall have resulted in plants’ adaptation to alternating periods of excess water followed by drought conditions (Figure 9.25). Specifying these plants for bio-inﬁltration basins that are native to the region will lead to sustained porosity of the ﬁlter media, better growth, lower maintenance and better habitat for native species of insects, birds and mammals. In a Seattle, Washington (a climate with a long, dry period in the summer) study, bio-retention basins with longer drawdown times (24–72 hours) supported a different set of plants than basins that drew down in 24 hours. In the basins with more moisture (and longer inundation), the three most successful plants were Scirpus atrocinctus, Scirpus microcarpus, and Scirpus acutus, while in the drier basin Carex stipata, Carex pachystachya, Juncus tenui, Rubus spectabilis and Rosa pisocarpa grew well. Juncus effusus grew well under both moisture conditions (Reiners, 2008). See the Appendices for regional lists of plants suitable for bio-retention basins and rain gardens.
Treatment performance Stormwater management Assessment of several bio-retention basins conﬁrms that they are effective in reducing run-off volume, run-off rate and delaying the time of peak run-off. The Hal Marshall bio-retention basin (Figure 9.26) in Charlotte, North Carolina, was designed to capture storms of 1 inch or less. However, for rainfall depths of 1.65 inches (42 mm), the peak storm outﬂow decreased by 96 per cent even though the entire catchment
Figure 9.25 Plants can be treated formally, as in this Portland, Oregon, bio-infiltration basin, or more naturally to respond to the project context. This basin receives run-off from the street and sidewalk areas. Photo: Gary Austin, 2012.
STORMWATER MANAGEMENT 211 Figure 9.26 Hal Marshall bio-retention basin with spring growth of vegetation. Photo: North Carolina State University, Biological and Agricultural Engineering, William Hunt.
area was impervious. During the monitoring period, the mean storm was 1.08 inches (Hunt, 2008). This performance is conﬁrmed by a study of a bio-retention basin constructed at Villanova University in Pennsylvania. Its catchment area is 50,000 square feet and is 52 per cent impervious. The 4-feet-deep inﬁltration basin consistently removes 50–60 per cent of the storm run-off from the surface waters. In fact, for storms 1.95 inches and less, there is rarely any outﬂow from the basin at all. This is partly because there is inﬁltration into the subsoil during the entire storm. Even during a 6-inch storm, the retention basin reduced the storm peak run-off rate (Council, 2009). A University of New Hampshire bio-retention basin comprised of a 30-inch top layer of sandy media, and a 16-inch bottom layer of gravel, displayed an 82 per cent reduction in peak stormwater ﬂow and a 92-minute delay in the storm peak (University of New Hampshire, 2007).
Stormwater quality improvement The example below illustrates the water quality improvement data (Table 9.8) for the bio-retention basin at the Hal Marshall Municipal Services Building (Figure 9.26). It is designed to treat 1 inch (25.4 mm) of rainfall (the 2-year, 24-hour storm is 3.36 inches). The basin receives water from a 0.92-acre (0.37 hectare) parking lot. The surface of the inﬁltration bed is 2,480 square feet (229 m2), which represents 6.2 per cent of the catchment area. The bed is composed of 4-feet deep (1.2 m) loamy sand (silt/clay = 5.7 per cent) with a 6-inch diameter corrugated under-drain. The subsoil permeability is 0.43 inch per hour, and the basin is planted with a variety of water tolerant species (Hunt, 2008). The bio-retention bed reduces contaminants signiﬁcantly with one exception (Table 9.8). The low total nitrogen removal was due to low organic matter in the run-off. The increase in nitrite and nitrate to 0.43 mg/L indicates that the bed provides aerobic conditions for the conversion of ammonium to nitrite and nitrate. However, the removal of nitrate requires an oxygen-depleted environment, which is not a feature of this design. A very similar bio-retention bed was installed in Greensborough, North Carolina, but the bottom 2 feet was saturated with water to form an anaerobic zone. This bed performed better with nitrate removal at 75 per cent and total nitrogen removal of 40 per cent.
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The Charlotte bio-retention basin signiﬁcantly reduced faecal coliform bacteria (89 per cent) and E. coli (92 per cent). The bio-retention basin outﬂow met EPA recommendations for primary recreation contact for E. coli and almost met the standard for faecal coliform bacteria concentration (Hathaway and Hunt, 2012). Drying of the soil between storms reduces pathogenic bacteria. As drainage through the soil media is rapid, even the temporary pool above the soils drops about 1 inch per hour after a storm. High oxygen levels return to the soil volume quickly, and drying is due, in part, to evapotranspiration of bio-retention beds (Hunt, 2008). A University of New Hampshire bio-retention basin (similar in design to the one in Figure 9.23) featured a 99 per cent removal effectiveness for zinc, which is better performance than the basin data shown in Table 9.8. The New Hampshire study also reported total hydrocarbon removal of nearly 60 per cent for a 30-inch-deep ﬁlter bed and 99 per cent for a 48-inch-deep bed (University of New Hampshire, 2007). Another study of PAH removal in a bio-retention basin reported an annual average PAH mass load reduction of 87 per cent (DiBlasi et al., 2009). A laboratory experiment that tested 125 ﬁlter media conﬁgurations, varied the plant, ﬁlter media, media depth and pollutant concentrations typical of urban stormwater. The signiﬁcant difference in the best performing conﬁguration was the presence of Carex appressa, which is characterized by deep and ﬁne roots. Under various media and ﬂow conditions, the best ﬁlter removed 99 per cent of TSS, 93 per cent of ammonium, 85–96 per cent of nitrite and nitrate, 71–79 per cent of total nitrogen, 93–96 per cent of total phosphorus and 87–98 per cent of particulate phosphorus. These are signiﬁcant improvements in performance compared to the Charlotte bioretention basin. The Australian study indicates that using sandy loam ﬁlter media, specifying plants that are known to remove ammonia and nitrate at accelerated rates (some plants actually increased total nitrogen in the efﬂuent), and avoiding compost or mulch in the media mix could lead to signiﬁcant improvements in water quality in full-scale ﬁeld applications (Bratieres et al., 2008). Phosphorus removal in bioretention basins is generally poor, ranging from 5 to 30 per cent. Mulch in the ﬁlter media and sands or gravel high in phosphorus cause low removal rates, or sometimes an increase in phosphorus in the outﬂow. Sedimentation and adsorption are the primary removal mechanisms for phosphorus. Using media with high levels of calcium, aluminium or magnesium results in good removal of phosphorus. Eventually the adsorption sites in the ﬁlter media will be ﬁlled, and removal rates will drop. Aluminium-based drinking water treatment residuals (a waste product) as an Table 9.8 Hal Marshall bio-retention basin (Charlotte, NC) pollution removal performance (Hunt, 2008) (from parking lot catchment area)
Outflow Removal (%)
Total nitrogen TKN Ammonium Nitrite and nitrate TSS BOD Total phosphorus
1.68 1.26 0.34 0.41 49.5 8.54 0.19
1.14 0.70 0.10 0.43 20.0 4.18 0.13
Faecal coliform E. coli Zinc Copper Lead Iron
14,700 4,500 69 938 273 71 72 17 77 12.8 5.9 54 4.85 3.33 31 1,110 4,710 330
32 44 73 –5 60 63 31
Outflow Removal (%)
(Hunt, 2007. City of Charlotte, Pilot BMP Monitoring Program, Hal Marshall Bio-retention) Units = mg/L, except for coliform and E. coli, which are CFU/100 ml.
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amendment to the bio-retention ﬁlter media improve adsorption of phosphorus in laboratory and ﬁeld studies (Stone, 2013). A laboratory scale study demonstrated 84–100 per cent removal of the common pesticide, atrazine, in bio-retention systems with and without an anaerobic stage (Yang, 2010).
Hybrid bio-retention basins When advanced water quality is the project goal, a sequence of treatment techniques is likely to provide better results than a single type. The alternation of oxygen-rich and oxygen-depleted environments often treats the widest range of contaminants. Ohio State University built and tested a three-stage bio-retention basin that demonstrates outstanding water quality improvement for both urban and agricultural contaminants. The system is designed to contain 1.76 inches (44.7 mm) of run-off from a 748-squarefeet (69.5 m2) paved surface, resulting in 3.1 m3 of run-off. This is equivalent to the 10-year, 1-hour storm (Yang et al., 2013). The system consists of three cells operated in series. The ﬁrst cell is a 1.2-m-deep vertical subsurface ﬂow basin that is always saturated with water. The second is a vertical ﬂow, free draining cell and the third is a gravel inﬁltration bed. The vertical ﬂow cells have an 8-inch (0.2 m) temporary pool, are planted and have a mulch layer. The ﬁrst cell (saturated) contains 2.8-feet-deep (0.85 m) ﬁlter media (90.6 per cent sand, 6.9 per cent silt, and 2.5 per cent clay with 0.7 per cent organic matter, 3.1 meq/100 g of cation exchange capacity, 12.0 cm/h of saturated conductivity). On top of this ﬁlter is a 0.5-foot-deep (0.15 m) layer of ﬁne gravel (3.2–12.7 mm diameter). With an area of 73 square feet (6.8 m2), the saturated cell can contain 56 cubic feet (1.58 m3) of water (1-inch rainfall from the paved surface). The area of the saturated basin is 9.6 per cent of the catchment. The plants in this basin are boneset (Eupatorium perfoliatum), spiderwort (Tradescantia ohiensis) and culver’s root (Veronicastrum virginicum) (Yang et al., 2013). The second cell can contain 1.34 m3 of water. The basin is 20 inches (0.5 m) deep and composed of ﬁlter media (0.35 m deep) above a 0.15 m depth of ﬁne gravel. The plants in this basin are purple love grass (Eragrostis spectabilis), Indian grass (Sorghastrum nutans) and purple coneﬂower (Echinacea purpurea) (Yang et al., 2013). Similar to Hal Marshall basin, the hybrid basin has good hydraulic performance. It reduces peak ﬂow 84 per cent and 88 per cent for medium rainstorms (6–12 mm/24 hours) and heavy rainstorms (more than 12 mm/24 hours). It reduces 59 per cent and 54 per cent of storm run-off volume, respectively, for medium and heavy rainstorms, and delays the time of peak ﬂow 180 minutes and 80 minutes, respectively, for medium and high intensity storms (Yang et al., 2013).
Table 9.9 Net mass removal (%) of pollutants from sequential urban run-off storms (Yang et al., 2013)
Average influent (mg/L) Maximum effluent (mg/L) Net mass removal (%)
Nitrate (NO3-N) Phosphate (PO4-P) Dicamba (C8H6Cl2O3) Glyphosate (C3H8NO5P) 2,4-D(C8H6Cl2O3)
20 10 0.09 2.0 0.3
6.9 2.5 0.05 0.08 0.25
78–91 94–99 84–92 98–99 81–90
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When tested with very high concentrations of common urban pollutants under simulated rainfall, the hybrid bio-retention basin removed as much as 91 per cent of the nitrate, 99 per cent of the phosphorus and 90–99 per cent of three pesticides common in urban run-off (Table 9.9). The tested pesticides were glyphosate (N-(phosphonomethyl)glycine), dicamba (3,6-dichloro-2-methoxybenzoic acid) and 2,4-D(dichlorophenoxyacetic acid) (Yang et al., 2013).
Base flow and ground water The traditional goals of ﬂood and channel protection are increasingly expanded with requirements for water quality improvement, and most recently with stipulations that post-development inﬁltration of rainwater shall approach the pre-development inﬁltration volume. This third phase of stormwater regulations is intended to preserve the base ﬂow of local streams and rivers. This is important to preserve minimum water levels required and ecosystem health. In addition, bio-retention with inﬁltration can be used to correct historic damage (channelization) to streams by reducing storm ﬂows and delaying storm peak ﬂows. Base ﬂow is the discharge of water into receiving streams by water moving through the soil volume. Declining base ﬂow volumes are known to reﬂect the increase of impervious surfaces within the watershed. Sufﬁcient base ﬂow is critical to the ecology of aquatic environments during the dry seasons. The volume, water quality and temperature of the base ﬂow are factors important to the health of streams. Regulations generally require that a portion of the pre-development inﬁltration volume is inﬁltrated after development. For example, the Wisconsin Department of Natural Resources requires that 25 per cent or 10 per cent of the 2-year, 24-hour, pre-development storm is inﬁltrated by residential and non-residential projects, respectively. Alternatively, the required inﬁltration volume may be calculated as 60 per cent (non-residential) or 90 per cent (residential) of the average annual predevelopment inﬁltration volume. The calculations exclude undisturbed natural areas.
Figure 9.27 The Street Edge Alternative project in Seattle demonstrated the effectiveness of bioretention for the dual purpose of mitigating high stormwater volumes that had damaged a stream and local flooding of the basements of homes in a residential district. The project reduced annual run-off from the neighbourhood by 99 per cent and eliminated basement flooding. Although some streets in the neighbourhood are fairly level, the linear infiltration basin shown here demonstrated techniques for steeper terrain (about 6 per cent). Photo: Gary Austin, 2011.
STORMWATER MANAGEMENT 215 Table 9.10 Reduced curve number and depth of rainwater to infiltrate
Hydrologic soil group B %I 0 1 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
RCN 61 63 65 67 68 70 72 74 75 78 80 81 83 85 87 89 91 92 94 96 98
55 60 64 65 66 66 68 70 71 73 75 77 79 81 82 84 87 89
55 61 62 63 63 66 67 68 70 72 74 76 78 79 81 84 86
55 58 59 60 60 62 64 65 67 69 71 73 75 76 78 81 83
55 56 56 58 60 61 63 65 67 69 71 72 74 77 80
55 58 60 62 65 66 67 70 73 76
55 57 59 61 62 65 69 72
55 59 63 66
55 57 59
I= Imperviousness. RCN = Runoff curve number. RE= Rainfall target.
Exemptions to the rule include areas with existing toxic soil and high seasonal ground water (Bannerman and Barras, 2004). Other agencies have similar methods of determining the volume of rainwater that must be inﬁltrated. For example, Prince George’s County, Maryland, determines the required inﬁltration volume in a more site-speciﬁc manner. Table 9.10 shows the values for areas with hydrologic soil type B. The table is used to determine the rainfall depth from impervious areas that are to be inﬁltrated after development, to mimic inﬁltration for native forest in good condition. One enters the chart in the left-most column (per cent imperviousness of the proposed development). From the per cent impervious cell, move right until the ﬁrst green cell is encountered, then read the rainfall depth in inches at the top of the column. For example, 50 per cent imperviousness yields 1.8 inches. This is adjusted by adding a coefﬁcient. The coefﬁcient is calculated with the formula: 0.05 + (0.009 × per cent impervious cover). For our example with 50 per cent imperviousness, this is 0.05 + (0.009 × 50) = 0.05 + (0.45) = 0.5. This coefﬁcient is multiplied by the rainfall depth 1.8 inches × 0.5 = 0.9 inches. Therefore, the inﬁltration that would be required to comply with the regulation is 0.9 inch of rainfall depth from the impervious area. If the impervious area of the proposed development was 10,000 square feet, then 750-cubic-feet volume of water would require inﬁltration, 10,000 × (0.9 inches/12 inches) = 750 cubic feet (Maryland Department of the Environment, 2009). Other methods of determining the volume of water use the difference between the TR-55 curve number for pre- and post-development. For example, a wooded site slated for low-density residential development might typically have a pre-development
216 STORMWATER MANAGEMENT Figure 9.28 Stormwater collection and infiltration can be accommodated in the urban landscape. Landscape architects are beginning to explore the multifunctional and aesthetic potential of stormwater landscapes. This courtyard is one of several that are designed to receive stormwater in a park in Tianjin, China. These are beautiful as well as intriguing places for children and adults. Photo: Kongjian Yu, 2014.
Figure 9.29 This Oregon City bio-retention basin receives stormwater runoff from a highway. Note the steel grate over the channel that delivers water from the gutter to the basin (lower left). The steel panels in the basin are sculptural elements that contrast the plants, which range from drought tolerant upland species to water tolerant plants in the bottom of the basin. The design is by Greenworks. Photo: Gary Austin, 2013.
curve number of 55. If after development, the wooded site had a curve number of 70, then 15 per cent more water is expected to run-off. An inﬁltration of 0.22 inches of run-off volume from the developed site would be required to match pre-development conditions for a storm with a 2-inch rainfall depth (Department of Environmental Resources, 2007). For a 1⁄2 acre site, this would equal approximately 400 cubic feet for a 2-inch storm, and could be accommodated in a 20-feet by 20-feet bio-retention basin.
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Conclusion Bio-retention basins are effective landscapes for the treatment of pollutants, stormwater management and groundwater recharge. The basin design must be adapted to site conditions and the primary implementation goal, but are more effective than stormwater detention and retention basins (Figure 9.29). Lower than desired removal of nitrates, phosphorus and chloride requires design modiﬁcation or additional treatment methods. Use of a saturated volume within the bio-retention basin improves nitrate removal. Even higher performance might be achieved (as it is in the treatment of wastewater) if a sequence of treatment stages is implemented (Guenter Langergraber and Roland Rohrhofer, 2009). This might be conﬁgured as a lined aerobic bio-retention basin followed by a lined anaerobic horizontal subsurface wetland and then an inﬁltration bed (Austin, 2010).
Qunli stormwater wetland case study Case studies, including this one of the National Urban Wetland Park in Qunli, expose the challenges and realities posed by context, diverse goals, budget, hydrology, soils, maintenance, construction quality, etc. This masterwork combines stormwater technology with innovative landscape architectural design, to demonstrate that multifunctional landscapes can simultaneously be beautiful social places (Figure 9.37), engineering infrastructure and regenerative ecosystems.
Context Qunli is a new town district located east of Harbin in northeast China (45°43′46.77″ N 126°33′45.29″ E). Figure 9.30 shows the Qunli area of Harbin in relationship to the Songhua River and the project site. At the centre of the developing urban district, the project site was an 84-acre (34 hectares) degraded wetland. The hydrological isolation created by the new development and declining ground water levels was causing the wetland to decline. The climate of Harbin is relative dry. The city receives as much
Figure 9.30 Aerial view of the context for the stormwater park. The Songhua River is north of the park site (red asterisk). Photo: Google Earth and CNES Astrium, 45°43′46.77″ N 126°33′45.29″ E, image date: 15 September 2014, image accessed: 2 April 2015.
218 STORMWATER MANAGEMENT Figure 9.31 Aerial view of site. Longest dimension about 2,000 feet (650 m). Photo: Google Earth and CNES Astrium, 45°43′32.81″ N 126°32′53.38″ E, image date: 15 September 2014, image accessed: 2 April 2015.
Figure 9.32 The land-use plan of the Qunli New Town shows the distribution of high-density residential (yellow), commercial mixed-use (red), residential mixed-use (orange) and open space (green). Image: Kongjian Yu, 2009.
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as 70 per cent of its 22 inches (567 mm) of annual precipitation from June to the end of August, although snow is a signiﬁcant complication in this temperate climate. The aerial image of the site (Figure 9.31) and the land-use plan (Figure 9.32) graphically illustrate the high population density of both workers and residents around the parcel. The Qunli New Town is an example of an emerging district (6,753 acres, 2,733 hectares) that will be the home and workplace for a population of approximately 350,000 people. However, the product of high-density urban districts is the creation of a highly impervious urban environment. At Qunli, nearly 344 million square feet (32 million m2) of building ﬂoor area and impervious infrastructure will consume all but 16.4 per cent of the permeable landscape (Saunders and Yu, 2012).
Design The parcel had been originally set aside as future parkland. The simultaneous need for public open space and the need to preserve and restore the existing wetland was resolved by the designer, Kongjian Yu. His plan invites the public to participate along the perimeter, while preserving most of the ecosystem at the centre of the parcel. The designer established a pattern of birch forest wedges (Figure 9.33) separated by shrub masses and stormwater ponds and wetland vegetation (Figure 9.34).
Figure 9.33 The plan view of the design for the stormwater park shows the mound (green) and pond perimeter landscape connected by paths and elevated boardwalks (red line). Image: Kongjian Yu, 2009.
220 STORMWATER MANAGEMENT Figure 9.34 Water basins in series collect water from the urban catchment. The transfer from the sedimentation basins (brown) to second stage (light blue) and third stage (dark blue) remove progressively more sediment and pollutants before the water is discharged into the recovering wetland. The light green wedges represent the upland mounds planted with tree groves. Image: Kongjian Yu, 2009.
Figure 9.35 Elevated walkways and pavilions create opportunities for dramatic views and places where groups can gather in the sun or shade. The design includes four pavilions with unique designs and materials. Photo: Kongjian Yu.
STORMWATER MANAGEMENT 221 Figure 9.36 One of the two viewing towers in the Qunli wetland park differ greatly in character, but are striking and provide wonderful views of the wetland and human activities. Photo: Gary Austin, 2015.
A network of paths and elevated boardwalks (about 2,500 feet, 762 m) punctuated by four pavilions (Figure 9.35) and two viewing towers (Figure 9.36) connects the stormwater and upland landscapes. The plan view of the project (Figure 9.33) shows an active and diverse perimeter dedicated to human uses, while the interior is dedicated to ecosystem functions without the disruption of paths and other human activity or facilities (with the exception of an electrical transmission line).
Stormwater management and treatment The increase in stormwater run-off volume and rate caused by urban development could pose signiﬁcant ﬂooding hazards to the new residents and those downstream, as saturated soils and ﬂooding were already a historic problem in the ﬂat plain of the Songhua River where Qunli New Town is being constructed. Furthermore, the inﬁltration of rainwater is required to restore a depleted groundwater volume. The project is designed to store and treat a water quality year storm in addition to the normal volume of water in the wetland. Larger storm ﬂows bypass the wetland through a conventional storm sewer (Figure 9.43) leading to the river. The catchment area for the wetland is about 111 acres (45 hectares) where the stormwater is collected in a conventional system of catch basins and stormwater pipes. These distribute the
222 STORMWATER MANAGEMENT Figure 9.37 This image shows the sedimentation basins at work as well as the mounds forested with birch trees (Betula pendula). Photo: Kongjian Yu, 2011.
Figure 9.38 Birch groves (Betula pendula) on hillocks are a counterpoint to the sedimentation and treatment ponds that prepare the stormwater for entrance into the wetland. The stormwater collection areas vary in size, depth and vegetation. Photo: Gary Austin, 2015.
Figure 9.39 Frequency and depth of inundation determine the range of species around or within each treatment basin and in the core wetland. Photo: Kongjian Yu, 2011.
STORMWATER MANAGEMENT 223 Figure 9.40 The stormwater flows from basin to basin via an underground pipe in order to maintain a low peak flow rate. However, emergency spillways are provided between the sedimentation and treatment basins, and require careful site grading and sizing of culverts. Photo: Gary Austin, 2015.
stormwater evenly to more than 50 sedimentation ponds along the perimeter of the park. Water from the sedimentation basins overﬂow into more than 80 secondary and tertiary treatment basins. These in turn overﬂow into the 50-acre (20.2 ha) core wetland. Figure 9.38 illustrates a second tier sedimentation and treatment pool and a birch grove, formed through a balanced cut and ﬁll earthwork to create a pool and mound landscape along the perimeter of the park. The wetland park has proven to be very effective for both ﬂood management and water quality improvement. It is estimated that under normal conditions, the wetland contains 58 acre feet (72,000 m3) of water, while at maximum storage it holds more than 111 acre feet (138,000 m3) of water (Yan, 2013). Water ﬂows via gravity from the sedimentation basins to the treatment basins (Figure 9.40) and to the core wetland. Low velocity inﬂow and sufﬁciently sized sedimentation basins allow particles to settle. A rule of thumb is to accommodate 10–25 per cent of the water quality storm in the sedimentation basins. Controlling erosion on-site is a critical issue, as the removal of sediment before it reaches the core wetland and even the sedimentation basins, if possible, will prolong the life of both. Figure 9.41 shows that the water from slopes is intercepted in slotted drains covered with coarse gravel. Using erosion control blankets or mulch on slopes is particularly important until the vegetation on the slope can completely cover the soil. Similarly, the velocity of water entering the sedimentation basins must be moderated to allow settling of the heavier sediments before the water overﬂows into the next treatment basin. Figure 9.42 shows ponds after a storm, and water further away that receives the ﬂow after much of the sediment has been deposited. The sediment in the basins can
224 STORMWATER MANAGEMENT Figure 9.41 Sediment and velocity control on-site. Photo: Gary Austin, 2015.
be periodically removed to avoid ﬁlling the wetland and shortening its life. Cleaner water ﬂows from the sedimentation pools into the wetland, restoring the natural hydrology and native vegetation (Yan, 2013). However, since the groundwater level has dropped, restoration of the natural wetland requires supplemental water during the dry season. This is provided by water pumped from the river (Figure 9.43). This practice might be suspended if projects similar to this one recharge the aquifer. The visual character of the wetland changes dramatically with the season. Specifying plants that bloom (Figures 9.44 and 9.39) in different seasons maintain colour and detail in the park for many months (Figure 9.46). The enormous increase in biomass during the growing season conceals the water with tall green growth. In autumn, the wetland landscape is golden and, in winter, it is ice and snow covered (Figure 9.45). The ﬁlling and draining of the sedimentation and treatment basins is another temporal aspect of the design. This makes stormwater (and the monsoon rains) visible to the user and creates an ever-changing scene. As water in the basins inﬁltrate or evaporate, capacity for the subsequent storm is created. The sedimentation and treatment pools on the perimeter of the wetland capture sediment and the attached heavy metal and bacteria.
Figure 9.42 Sedimentation basins connect to treatment pools and then to the core wetland. Photo: Kongjian Yu, 2011.
STORMWATER MANAGEMENT 225 Figure 9.43 Water from the nearby river supplements the wetland during the dry season. In the wet season, this structure conducts overflow to the river. Photo: Gary Austin, 2015.
Figure 9.44 Siberian iris blooming in May. Photo: Gary Austin, 2015.
Figure 9.45 Texture and colour of the wetland vegetation provides terrific aesthetics even after the first frost of autumn. Photo: Kongjian Yu, 2014.
226 STORMWATER MANAGEMENT Figure 9.46 The Qunli wetland and park offer great seasonal variety. Photo: Kongjian Yu, 2011.
Ecosystem services The designer adopted a strong ecosystem service perspective as the foundation for the application of design and technology. The wetland park provides ecosystem beneﬁts to humans. The stormwater and wetland restoration goals are met through the use of regenerated hydrology and the planting of native plants. The vegetation extends the efforts of the landscape architect by organizing itself according to tolerance to saturated soils. This is key to the low maintenance of the park. Critical ecosystem services are the stormwater storage (ﬂood protection), cleansing of non-point source pollution and inﬁltration of the treated water through a recovered wetland to augment the ground water supply (Figure 9.47). Three methods of providing water to restore the damaged wetland were investigated. Pumping groundwater into the wetland is problematic due to the cost, poor water quality and the fact that groundwater depletion is one of the reasons for the decline of the natural wetland. Pumping water from the Songhua River also comes with an energy cost. The use of urban stormwater is the least expensive option, and the quality of the water is intermediate between water from the river and groundwater (Yan, 2013). Related human beneﬁts are the stimulation of high-value urban development and the provision of open space, recreation and social opportunities. These are in great demand due to the very high population density. Therefore, the design creates a range of opportunities and experiences for individuals and groups. Although city views are highlighted at times, the wetland park is a sanctuary for people and a dramatic contrast to the street, plaza and ornamental landscape environment that surrounds the park. Literally steps away from towering residential buildings, a family can ﬁnd a cosy deck enclosed by native trees (Figure 9.48). The several pavilions are beautifully and creatively designed with local materials. The contrast of the cordwood, stone (Figures 9.49, 9.50 and 9.51), metal, brick and bamboo material makes each pavilion a destination and unique experience. Each structure is a unique setting that features a shady space and a commanding view. The two towers provide the most dramatic viewing opportunities (Figures 9.36 and 9.53) (and good exercise).
STORMWATER MANAGEMENT 227 Figure 9.47 The restored hydrology supports the low maintenance cost of managing the vegetation and provides seasonal diversity. Photo: Kongjian Yu, 2011.
Figure 9.48 There are many spaces for small groups. Photo: Gary Austin, 2015.
Figure 9.49 This pavilion provides shade to the user with a novel use of native stone contained in a wire frame. The extension into the landscape provides wildlife viewing and views of the surrounding city buildings. Photo: Gary Austin, 2015.
The landscape and habitat diversity is even greater than the variety of human settings. Gradients between upland and wetland vegetation, shallow and deep water create niches for many species. Limiting human activity to the perimeter of the wetland provides wildlife with a refuge from disturbance that so often limits the variety of species that might share the urban landscape with people. As the native plant species respond to the restored hydrology and cleaner water, and grow to provide a vertical as well as horizontal distribution of niches, the number and variety of species present will grow. The great production of plant biomass is responsible, in part, for the energy available for long food chains that begin with herbivores (Figure 9.52).
228 STORMWATER MANAGEMENT Figure 9.50 A pavilion made of bamboo screen. Photo: Kongjian Yu, 2011.
Figure 9.51 Winter scene of the pavilion made from cord wood. Photo: Kongjian Yu, 2011.
Figure 9.52 The high production of biomass by the wetland plants transfers energy to other tropic layers. This creates a highly diverse ecosystem of plants, herbivores, predators and even decomposers. Photo: Gary Austin, 2015.
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Conclusion The urban design team, led by Turenscape, devised a sustainable plan that provides ecosystem services in every category through careful planning and design. The project goals include aesthetic, social, recreational, engineering and ecological dimensions, which the designer conceptualizes as ecosystem services, following the 2005 Millennium Ecosystem Assessment framework of regulating, supporting, provisioning and cultural categories. The planning and design masterfully create values in each of these ecosystem service categories. In the regulating category, we ﬁnd carbon sequestration in the biomass of the wetland vegetation and tree groves as well as in the reduction in the urban heat island temperature. In the supporting category, we ﬁnd the development of soil and recycling of nutrients and water. In the provisioning category of ecosystem services, we ﬁnd water cleaned and returned to the groundwater or river. The many beneﬁts in the cultural category include economic development, recreation, open space and aesthetic values (Figure 9.53). We can correctly describe this as a regenerative project, leading to better urban sustainability. The multifunctional mission of this project increases the complexity of planning, programming, design and implementation, but not necessarily increased complexity of materials or forms. Public open space, recreation and social space are needed to mitigate population density and the absence of private open space. The aspects of the design that restore or preserve ecosystem health mitigate the widespread and sometimes devastating impacts of rapid urbanization on adjacent natural and rural areas.
Figure 9.53 This image shows a variety of user amenities as well as a dramatic seasonal display of perennial flowers. Photo: Kongjian Yu, 2011.
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health, and stormwater management,” Environmental Science and Technology, vol. 46, no. 6, pp. 3039–3045, March 2012. Mallin, M. “Pollutant removal efﬁcacy of three wet detention ponds,” Journal of Environmental Quality, vol. 3, pp. 654–660, 2002. Mallin, M. A., McAuliffe, J. A., McIver, M. R., Mayes, D. and Hanson, M. A. “High pollutant removal efﬁcacy of a large constructed wetland leads to receiving stream improvements,” Journal of Environmental Quality, vol. 41, no. 6, p. 2046–2055, 2012. Maryland Department of the Environment, “2000 Maryland stormwater design manual, vol. 1, 2009 revision.” Maryland Department of the Environment, 2009. National Oceanic and Atmospheric Administration, “Atlas 2, Volume 5, Precipitation Frequency Atlas of the Western United States, (1973),” 1973. [Online]. Available: http://hdsc.nws.noaa. gov/hdsc/pfds/other/id_pfds.html. [Accessed: 12 July 2016]. Peters, N. E. “Effects of urbanization on stream water quality in the city of Atlanta, Georgia, USA,” Hydrological Processes, vol. 23, no. 20, pp. 2860–2878, 2009. Reiners, J. “Vegetation growth and success as a function of soil moisture conditions in bioretention cells,” 2008. Roseen, R. M., Ballestero, T. P. and Houle, J. J. “UNHSC subsurface gravel wetland design speciﬁcations,” 2009. Roseen, R., Ballestero, T., Houle, J. and Loram, A. “Subsurface gravel wetlands for stormwater management,” Stormwater Report, 2012. [Online]. Available: http://stormwater.wef.org/ 2012/07/subsurface-gravel-wetlands-for-stormwater-management/. [Accessed: 12 July 2016]. Saunders W. S. and Yu, K. eds., Designed ecologies: The landscape architecture of Kongjian Yu. Basel: Birkhäuser, 2012. Schipper, L. A., Robertson, W. D., Gold, A. J., Jaynes, D. B. and Cameron, S. C. “Denitrifying bioreactors – An approach for reducing nitrate loads to receiving waters,” Ecological Engineering, vol. 36, no. 11, pp. 1532–1543, 2010. Spetzman, J. “Phosphorus in lawns, landscapes and lakes,” Minnesota Department of Agriculture, 2004. State of Delaware, “DelDOT Road Design Manual.” State of Delaware, 2008. Stone, R. “Evaluation and optimization of bioretention design for Nitrogen and Phosphorus removal,” Civil Engineering, University of New Hampshire, 2013. Tiefenthaler, L. L., Schiff, K. and Bay, S. “Characteristics of parking lot run-off,” Southern California Coastal Water Research Project, Long Beach, California, SCCWRP Technical Report #343, 2001. University of New Hampshire, “Annual report,” CICEET, Durham, NH, 2007. US Environmental Protection Agency, “Aquatic life ambient water quality criteria for Ammonia – Freshwater,” Ofﬁce of Science and Technology, Washington DC, EPA 822-R-13-001, 2013. US Environmental Protection Agency, “National Pollutant Discharge Elimination System (NPDES) permit writers’ manual,” EPA-833-K-10-001, 2010. US Environmental Protection Agency, “National rivers and streams assessment 2008–2009: A collaborative survey,” US Environmental Protection Agency, Washington DC, DC 20460 EPA/841/D-13/001, 2013. US Environmental Protection Agency, “Nitrogen and phosphorus in streams in agricultural watersheds,” February 2010. [Online]. Available: http://cfpub.epa.gov/eroe/index.cfm? fuseaction=detail.viewInd&lv=list.listbyalpha&r=219683&subtop=200. [Accessed: 8 June 2015]. USDA (US Department of Agriculture), “Part 630 hydrology national engineering handbook,” US Department of Agriculture, 210–VI–NEH, 2007. USDA (US Department of Agriculture), “Urban hydrology for small watersheds,” Technical Release 55, 1986.
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Virginia Department of Environmental Quality, “Virginia stormwater design speciﬁcation No. 13, Version 2.0,” 2013. Yan, L. “Evaluation of ﬂood regulation and storage capacity in Harbin Qunli National Urban Wetland Park,” Modern Landscape Architecture, vol. 10, no. 1, pp. 43–50, 2013. Yang, H. “Dissolved nutrients and atrazine removal by column-scale monophasic and biphasic Rain Garden Model Systems,” Chemosphere, vol. 80, pp. 929–934, 2010. Yang, H., Dick, W. A., McCoy, E. L., Phelan, P. L. and Grewal, P. S. “Field evaluation of a new biphasic rain garden for stormwater ﬂow management and pollutant removal,” Ecological Engineering, vol. 54, pp. 22–31, May 2013.
10 Increasing the sustainability of agriculture Introduction Generally, the objective of ‘sustainable development’ is applied to the design and construction of urban buildings and infrastructure within in cities and towns. Failure to implement sustainable practices in the enormous land areas that support these urban centres ignores the impacts with regional or global implications. This is the reason for this review of agricultural practices and the application of constructed wetlands to reduce the amount of toxic chemicals and excess nutrients that compromise human and environmental well-being. Agriculture consumes more water than any other economic sector. Most of this comes from surface waters and may be nearly potable, if the source has not been greatly contaminated by poorly treated sewage, agricultural run-off or industrial discharges. Some of the water used by agriculture is pumped from aquifers. Therefore, the issue of water supply and its allocation is the ﬁrst sustainability concern. The amount of water withdrawn from either groundwater or surface water must be limited to the recharge rates of aquifers and the minimum requirements of healthy aquatic ecosystems. In some cases, such as at dairies and aquaculture operations, process water can be cleaned by constructed wetlands and reused to conserve potable supplies. Where this is possible, it is irresponsible to use precious potable water for non-potable uses. The agricultural sector is diverse. It can be divided conveniently into animal and ﬁsh operations and plant crop operations. Each of these is characterized by different point and non-point source pollution by-products that can be reduced by treatment wetlands (Figure 10.1). There are tremendous opportunities to improve the sustainability of agricultural operations due to their diversity and the enormous quantities of organic material, fertilizers and pesticides that currently mix with process water or stormwater and drain to natural water bodies.
Application of constructed wetlands in plant operations Introduction The production of commodity crops, such as corn, rice, wheat and cotton, is supported by large quantities of fossil fuels, insecticides, herbicides and artiﬁcial fertilizers.
234 INCREASING THE SUSTAINABILITY OF AGRICULTURE Figure 10.1 This is a constructed wetland at a field edge that receives agricultural drainage water to capture excess nutrients and pesticides. When designed in concert with tile drainage systems, the water in the wetland can be used to irrigate fields during drought years. Photo: Peggy Greb, USDA, Agricultural Research Service. License: government work product.
Stormwater run-off, wind and inﬁltration into groundwater transfer these pesticides and fertilizers to the aquatic environment. Often, the quantities of these pollutants overwhelm the capacity of the ecosystem to sequester or transform them into less harmful substances. In this case, engineered wetlands can restore the balance through treatment of contaminates near the source. The ﬁrst example of this is a natural wetland that was targeted to receive ﬁeld run-off decades ago. The wetland provides a model that we can use to design and locate constructed wetlands to make agriculture more sustainable.
Free water surface wetland for pesticide and nutrient reduction The use of a linear riparian wetland to remove total suspended solids (TSS), nitrogen, phosphorus and three common agricultural pesticides was extensively studied in Mississippi, USA. The site is along the Coldwater River (34°40′04.93″ N, 90°13′38.09″ W), where the ﬂoodplain has a low gradient resulting in many backwater channels and wetlands (Figure 10.2). In this case, the linear wetland is naturally severed from the main stem of the river. However, approximately 865 acres (350 hectares) of agricultural ﬁelds drain ﬁrst into drainage ditches leading to an intermittently wet slough, which discharges into the wetland. The riparian wetland was modiﬁed through
INCREASING THE SUSTAINABILITY OF AGRICULTURE 235 Figure 10.2 The field run-off enters the wetland at the left and flows toward the Coldwater River on the right. Photo: Google Earth, 34°40′04.93″ N 90°13′38.09″ W, image date: 10/15/2014, image accessed: 12/5/2015.
the construction of two adjustable crest weirs for research purposes. The upstream weir serves as a dam to create an upstream pool and the inlet to a linear wetland that is 1,640 feet long (500 m), 66 feet wide (20 m), with an average depth of 11 inches (28 cm) (Figure 10.3) (Lizotte et al., 2012). A simulated storm event equivalent to about a 1 cm rainfall from a 39.5-acre (16 hectares) ﬁeld and with a very similar hydrograph to a measured natural storm hydrograph was routed through the riparian wetland by lowering the upstream weir and injecting contaminants to match concentrations measured in the slough when water was present. The peak ﬂow into the wetland was 1,350 gallons per minute (85 litres per second) and the volume was 161,409 gallons (611 m3). The simulated storm did not result in outﬂow from the downstream weir. However, the inﬂow resulted in a pulse through the wetland. Results from a chemical tracer study revealed that within about 5 hours, the pulse reached the outlet (500 m). Outﬂow occurred 22 days after the simulated storm due to a local thunderstorm (Lizotte et al., 2012). Before the simulated storm was applied, the concentrations of contaminants were measured at six points along the wetland (0, 10, 40, 100, 300 and 500 metres from the inlet). The concentrations were: TSS – less than 100 mg/L at each location, total phosphorus – less than 1 to 3.4 mg/L, soluble phosphorus – 0.02 to 0.16 mg/L, ammonia and nitrite – less than 0.02 mg/L at each location, nitrate – 0.03 to 0.05 mg/L, total nitrogen – 2 to 6.7 mg/L and the target pesticides – below detection at all locations. During the ﬁrst 1.3 hours of the simulated storm, the following amounts of contaminants were introduced into the ﬂow: 270.8 kg sediment, 3.6 kg P2O5, 6.1 kg NH4NO3, 6,600 milligrams of a. i. atrazine + 5,220 milligrams of a. i. S-metolachlor (Bicep II Magnum®) and 630.4 milligrams of a. i. permethrin (Hi Yield 38®). A tracer of 200 grams NaCl allowed the movement of the contaminants within the wetland to be followed over time and distance (Lizotte et al., 2012). The simulated storm added TSS at a concentration of 375 mg/L (higher than the natural inﬂow concentration of about 325 mg/L). The water quality parameters were measured at a point 100 m from the wetland inlet at 1, 1.5, 2, 2.5, 3, 3.5, 4 and 5 hours and at 28 days after the beginning of the simulated storm (Table 10.1). Through ﬁltration and sedimentation, the wetland removed 90–98 per cent of TSS within
236 INCREASING THE SUSTAINABILITY OF AGRICULTURE Figure 10.3 Biologist Charles Bryant and Richard Lizotte measured water quality in the linear wetland. Pesticides entering upstream degraded quickly in the wetlands before reaching the downstream areas. Photo: Richard Lizotte, USDA, Agricultural Research Service. License: government work product.
48 hours. Total phosphorus declined from a concentration of 3.94 mg/L at 3 hours, to 1.33 mg/L at 5 hours and 1.05 mg/L at 28 days. Soluble phosphorus declined from a peak concentration of 3.44 mg/L at 2 hours, to 0.25 mg/L at 5 hours. Ammonia peaked at 2 hours at 0.42 mg/L, and declined to 0.06 mg/L at 5 hours. Nitrate levels were quite low, peaking at only 0.06 mg/L at 1 hour, and declining to 0.03 mg/L 4 hours before rising again to 0.05 mg/L at 5 hours. Total nitrogen peaked at 7.14 mg/L at the 2-hour measurement, and declined to 2.36 mg/L at 4 hours before rising again slightly to 2.81 mg/L at 5 hours. Overall the treatment effectiveness of the linear wetland was very high (Lizotte et al., 2012). The pesticides measured in this study are commonly applied to crops in the United States. Atrazine is one of the most widely used herbicides in the United States and is the herbicide most often encountered in drinking water supplies. Atrazine disrupts the endocrine system and was banned in the European Union in 2004 due to high levels in drinking water. S-metolachlor is a herbicide that accumulates in ﬁsh. Permethrin is a common synthetic, broad-spectrum insecticide that is used on crops, such as cotton, alfalfa, maize and wheat and on ornamental turf. It is a likely carcinogen and is highly toxic to ﬁsh and cats. All of the pesticides reached their peak concentration at the 100-m point 1.5 hours after the beginning of the simulated storm. Atrazine peaked at 145.66 g/L, and declined to 19.69 g/L at 5 hours, and was undetectable at 28 days. S-metolachlor
INCREASING THE SUSTAINABILITY OF AGRICULTURE 237 Table 10.1 Sediment (mg/L), nutrient (mg/L) and pesticide (g/L) concentrations in the wetland at 100 m from the inlet (Lizotte et al., 2012)
TSS Total PO4–P Soluble PO4–P NH4+–N NO3–N NO2–N Total nitrogen Atrazine S-metolachlor cis-Permethrin trans-Permethrin
Time (h) 1
159 2.77 0.71 0.12 0.06 0.01 4.18 53.14 48.0 2.6 2.1
142 4.00 3.06 0.40 0.06 0.01 6.75 145.66 114.9 7.2 4.5
76 3.94 3.44 0.42 0.05 0.01 7.14 77.95 65.2 3.1 2.5
103 2.86 2.02 0.27 0.05 0.01 5.58 54.5 42.0 1.7 1.3
69 2.22 1.15 0.16 0.04 0.01 2.98 36.62 26.7 1.0 0.7
93 2.13 0.51 0.08 0.04 0.01 2.52 26.80 18.9 0.8 0.6
68 1.46 0.43 0.08 0.03 0.01 2.36 20.84 14.5 0.6 0.4
112 1.33 0.25 0.06 0.05 0.01 2.81 19.69 13.9 0.4 0.3
160 1.05 0.43 Ua 0.07 0.02 4.07 Ub Uc 0.1 0.1
Ua Below detection limit of 0.02 mg/L Ub Below detection limit of 0.01 g/L Uc Below detection limit of 0.1 g/L
also peaked at 114.9 g/L, then declined to 13.9 g/L at 5 hours, and to undetectable levels at 28 days. Cis-Permethrin peaked at 7.3 g/L, and declined to 0.04 g/L at 5 hours. Trans-Permethrin peaked at 4.5 g/L, and declined to 0.3 g/L at 5 hours (Lizotte et al., 2012).
Field edge free water surface constructed wetland The example below is a more common situation where a constructed wetland is created at the edge of a ﬁeld to protect receiving streams and rivers. Red River Research Station in Louisiana constructed an agriculture run-off treatment system including sedimentation basins, a 4.5-acre (1.82 hectares) shallow wetland cell 18 inches deep (0.53 m) and a 10-acre (4.04 hectare) pond with a maximum depth of 9 feet (2.3 m) (Figure 10.4). The deep pond can hold about 18,000 m3. The wetland receives run-off from 400 acres (162 hectares) of farmland (3.6 acres of wetland per 100 acres of run-off) (Millhollon and Dans, 2010). Water samples taken at the ﬁeld edge and in the shallow wetland and deep pond reveal a reduction in the average concentrations of organic nitrogen and ammonia (65 per cent, to about 1 mg/L), total phosphorus (59 per cent, to about 1mg/L), soluble reactive phosphorus (45 per cent, to about 0.7 mg/L) and TSS (90 per cent). Nitrate was reduced to less than 0.5 mg/L. The wetland reduces pollutants entering the nearby, impaired Flat River, which the US Environmental Protection Agency (EPA) targets with a 30 per cent reduction in nitrogen and 62 per cent reduction in phosphorus (Jeong, Girouard and Colyer, 2015). These examples demonstrate that riparian free water surface wetlands can sequester or degrade contaminants common in agricultural run-off during small to moderate rainfall events. These events generally account for the greatest concentrations of contaminants. Although the example of the wetland along the Coldwater River was a natural wetland, it had been modiﬁed to receive agricultural run-off from a large watershed. The addition of weirs allowed the hydrology of the wetland to be controlled seasonally or for contaminant treatment purposes. Constructed wetlands
238 INCREASING THE SUSTAINABILITY OF AGRICULTURE
Figure 10.4 The Red River Research Station constructed wetland features a deep pool (foreground), shallow wetland and sedimentation basins. Photo: Google Earth 32°24′57.78″ N 93°37′48.74″ W, image date: 10/29/2104, image accessed: 9/15/2015.
could be designed based on this model, to achieve similar outstanding treatment results. The Coldwater River study demonstrated that 40–80 per cent of nitrogen and phosphorus, and 80–98 per cent of the target pesticides were removed within 300 m of the wetland inlet. Capturing or degrading these contaminants protects the main stem of the river from agricultural non-point source pollution (Lizotte et al., 2012). Figure 10.3 shows a highly diverse landscape that is well structured vertically. It is certainly a regional wildlife refuge. The Red River Research Station example shows that similar results can be achieved in edge-of-ﬁeld free water surface wetlands.
Horizontal subsurface flow wetlands for nitrate reduction in field run-off Dead zones In the examples above, the concentration of nitrate entering the wetland was low. This is often not the case. High nitrogen levels, primarily due to agricultural run-off, in rivers are largely responsible for the oxygen-depleted (hypoxic) zones in coastal waters, although concentrated livestock feeding operations and treated municipal sewage efﬂuent also contribute nitrogen to rivers. It is quite certain that agricultural sources are the primary cause of the dead zones due to a natural large-scale experiment. A 15,400 square mile (40,000 km2) dead zone in the Black Sea developed, as the use of artiﬁcial fertilizer and the presence of livestock operations (especially pig farms) doubled the amount of nitrogen and phosphorus entering the sea. The result was the collapse of the ecosystem and shellﬁsh populations. When the Soviet Union collapsed in 1989, artiﬁcial fertilizers were too expensive for farmers to purchase and many of the huge swine farms failed. The abrupt decrease in nutrient rich run-off resulted in a dramatic reduction in the area of the dead zone and the eventual recovery of the shellﬁsh ecosystem (Mee, 2006).
INCREASING THE SUSTAINABILITY OF AGRICULTURE 239
The concentration of dissolved oxygen in the water in hypoxic areas is often so low that aquatic organisms cannot survive. The nitrogen-rich water from the river causes explosive growth of phytoplankton (Figure 10.5) in the coastal areas. When these die, bacteria decompose the organic matter and consume almost all of the dissolved oxygen in the process. The drop in oxygen causes mass deaths in populations of ﬁsh and other organisms. The number (now more than 400) and size of the dead zones are increasing and are particularly problematic in the temperate waters of the northern hemisphere (Figure 10.6). The dead zone near the Mississippi River occupies 5,000–6,000 square miles and is well known, but hypoxic zones are emerging on both coasts of North America, Europe and China. These zones are clear indications of ecosystems out of balance and the imbalance is caused by unsustainable human development. Capturing and removing phosphorus and nitrogen, especially in the form of ammonia and nitrate, are urgently needed measures to restore ecosystem health and long-term human wellbeing.
Denitrifying wetlands Especially where stormwater and residual water from irrigation are drained from ﬁelds through underground drain-tile networks, nitrates from artiﬁcially fertilized soil are problematic and drain via surface water to pollute rivers and coastal areas. Since nitrate
Figure 10.5 Phytoplankton bloom in the Bay of Biscay, France. Photo: Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC, 2004. License: government work product.
240 INCREASING THE SUSTAINABILITY OF AGRICULTURE
Figure 10.6 This image shows the distribution and size of dead zones along with ocean carbon content and human population density. Dark blue indicates high carbon content, while the brown hue indicates high human population density. The pink hue indicates dead zones with the largest circles indicating zones 3,860 square miles (10,000 square km2). The black dots show the location of dead zones of unknown size. Image: NASA Earth Observatory, 2008. License: government work product.
is soluble, it can inﬁltrate through the soil to reach ground water. Edge-of-ﬁeld constructed wetlands have been developed to remove nitrate from the drainage system efﬂuent. These are horizontal subsurface ﬂow wetlands that use carbon (usually in the form of wood chips) as the ﬁlter media, instead of gravel, as in the treatment of domestic sewage. The principle is the same, however. Nitrate-rich water ﬂows through the ﬁlter media where oxygen is depleted. This environment encourages the growth of bacteria that uses nitrate as its energy source, resulting in nitrogen gas as a harmless by-product (Schipper et al., 2010). Figure 10.7 illustrates that the denitrifying wetlands are simple to construct and require little or no maintenance. The porosity of the ﬁlter material is quite high so ﬂow-through is rapid. The wetland should be lined with clay or a synthetic liner if there is a chance that the water can inﬁltrate into the groundwater. Since the wood chips are under saturated, oxygen-depleted conditions, they decay slowly, resulting in a lifespan of as much as 15 years. Overﬂow spillways or pipes can be added to the wetlands if necessary. Similarly, large denitrifying wetlands can be divided into cells to improve uniform distribution of the polluted water and to increase retention time (Schipper et al., 2010). Denitrifying wetlands can be located along ﬁeld edges to limit the displacement of crops and operate via gravity and very little maintenance. Studies of installed denitrifying wetlands show a reduction of 2 to 22 grams of nitrogen per m3 of ﬁlter material per day. The higher removal rates are associated with higher concentrations of nitrate in the inﬂow and higher seasonal temperatures. At temperatures as low as
INCREASING THE SUSTAINABILITY OF AGRICULTURE 241 Figure 10.7 In this transparent perspective of a denitrifying wetland, the water enters from drain tiles at the left and is distributed across the wetland. The polluted water flows through the wood chip filter and is collected and discharged to the right. The wetland can be vegetated (with reed canary grass, for example) and harvested. It is best if fully nitrified run-off enters the wetland as the last stage in a treatment sequence, as neither phosphorus nor ammonia are removed well by this wetland. Image: Gary Austin after Schipper (Schipper et al., 2010).
1–5°C, removal of about 2 grams of nitrogen per m3 per day is still evident. It appears that a range of high nitrate concentrations (3.1–49 mg/L) results in a consistent nitrate removal rate by the denitrifying wetland. At lower concentrations, as in urban stormwater, the removal efﬁciency may increase with increasing nitrate concentration (Schipper et al., 2010). At an inﬂuent temperature of 19°C and greater and a nitrate concentration of 66 mg/L, nitrate is reduced to nearly 0 mg/L within 7.5 feet of the inlet (Haunschild, Leverenz and Darby, 2010). A denitrifying wall is similar to the horizontal ﬂow wetland discussed above, it is situated to intercept groundwater along its side rather than top surface to remove nitrate that has already contaminated the groundwater basin. See the section on dairy operations for an example of a denitrifying wetland applied to livestock waste.
Application of constructed wetlands in animal operations Commercial scale production of livestock generates staggering amounts of organic waste and contaminated water (Figure 10.8). The quantities vary according to the type of animal production and whether it is concentrated, as in feedlots and dairies, or dispersed, as in pasture operations. Constructed wetlands of all types have been applied to the treatment of wastewater and stormwater from concentrated animal operations including dairies, feedlots, swine and chicken operations.
Feedlots and dairies Feedlots Although feedlots do not produce much wastewater, extremely high levels of nitrogen, phosphorus and other substances are part of the stormwater run-off from these facilities (Figure 10.9). Stormwater run-off from concentrated animal feeding operations can be dramatically cleaner after treatment by constructed wetlands before discharge into receiving streams and rivers.
242 INCREASING THE SUSTAINABILITY OF AGRICULTURE Figure 10.8 12 per cent of the phosphorus load in the Town Brook watershed in New York is from dairy cow dung deposited directly in pasture streams. This watershed is a major source of drinking water for New York City. Photo: Stephen Ausmus, USDA Agricultural Research Service. License: government work product.
The Beef Nutrition Farm at Iowa State University is an example of a four-stage treatment system (Figure 10.10), which treats stormwater from a farm with about 380 cattle. The ﬁrst stage is a shallow level concrete trough that receives run-off from the barn and outdoor feeding area. The feedlot is 56 by 756 feet. Although narrow, the settling basin width allows equipment to recover and compost the sediment. Liquid from the settling basin ﬂows through a pipe to a vertical subsurface ﬂow wetland planted with reed canary grass. Run-off from outdoor pens (34 inches by 110 feet) and additional farm area is also collected and delivered to the vertical ﬂow wetland. The third stage is a free water surface wetland, and the fourth stage is a vegetated swale and wet meadow. The area of the vertical ﬂow wetland (120 by 350 feet) is 20 per cent of its catchment area. The basin’s 2-feet high berm contains the 25-year, 24-hour storm. The detained water inﬁltrates through 5 feet of porous soil and is collected by three perforated pipes 4 inches in diameter. The efﬂuent from the subsurface wetland empties into a 90 by 150-feet free water surface wetland, 18 inches deep, which discharges into a vegetated swale and wet meadow and ﬁnally to Onion Creek (Lorimor, 2003). Table 10.2 illustrates the outstanding performance of the treatment sequence. The levels of all contaminants entering the vertical ﬂow wetland (settling basin efﬂuent) are very high. The vertical ﬂow wetland removes 80 per cent of the organic and ammonia nitrogen and 77 per cent of the phosphorus (Lorimor, 2003). The large
INCREASING THE SUSTAINABILITY OF AGRICULTURE 243 Figure 10.9 Stormwater drainage from a feedlot pen overflows into a basin where sediments can settle. Photo: Kongjian Yu.
Figure 10.10 Iowa State University Beef Nutrition Farm. A – Barn and feeding area; B – Concrete settling basin; C – Cattle pens; D – Vertical subsurface flow wetland; E – Free water wetland; F – Vegetated swale to stream. Photo: Google Earth, 42°03′23.70″ N 93°40′57.28″ W, image date: 11 June 2012, image accessed: 16 September 2015.
decrease in ammonia and the simultaneous increase in nitrate indicate very high nitriﬁcation and some denitriﬁcation, as the increase in nitrate is modest. The cost of the vertical ﬂow wetland was very low in this case, because the soil is porous; in other situations, excavation and replacement of clay soils would be necessary. Although the vertical ﬂow wetland area is excluded from grazing, the reed canary grass is harvested and fed to the cattle (Lorimor, 2003). The free water surface wetland further reduces contaminant concentrations as does the vegetated swale and meadow, with the exception of a large increase in nitrate.
244 INCREASING THE SUSTAINABILITY OF AGRICULTURE Table 10.2 Feedlot wetland performance (Lorimor, 2003). Five year averages except for Onion Creek data, which is a 2-year average. All units are mg/L
Effluent from settling basin Wetland inflow Wetland outflow Edge of Onion Creek Onion Creek upstream
Total Kjeldahl Nitrate and nitrogen nitrite
196.1 39.6 30.7 9.7 3.3
109 20.7 19.5 3.7 0.5
46.6 10.5 8.2 5.4 4.1
3,294.1 1,149.6 964.8 614.4 782.0
0.09 1.7 1.3 9.2 15.3
This suggests that the remaining ammonia is being converted to nitrate, but that conditions are inadequate for the conversion of nitrate to nitrogen gas. The addition of a nitrifying wetland as discussed earlier would eliminate most of this nitrate. The nitrate levels upstream of the farm indicate even higher levels of nitrate that would cause eutrophication in lakes. Although the treatment sequence dramatically reduced the amount of phosphorus, it is also at levels that would encourage eutrophication. Nevertheless, the overall reductions in Kjeldahl nitrogen (organic nitrogen and ammonia), ammonia and phosphorus of 95 per cent, 97 per cent and 88 per cent, respectively, are outstanding (Lorimor, 2003).
Dairies Dairies are similar to concentrated animal feeding operations (feedlots), as the density of animals is high, but dairies use a much greater volume of water to keep the animals, milking ﬂoors and equipment clean. At feedlots and dairies, manure accumulates rapidly. The solids are managed through composting, but the piles are generally open. Rainstorms cause leachate from the piles and run-off from the pens that is highly contaminated with sediment, excess nutrients and often with hormones and antibiotics (Figure 10.9). Dairy wastewater can be polluted with as much as 5,000 mg/L of BOD compared to the 4 mg/L of unpolluted streams. The BOD concentration of dairy wastewater is about three times higher than in swine wastewater. Concentrations of ammonia and nitrate and pathogenic bacteria are also particularly high. The US Clean Water Act speciﬁes that run-off from these facilities must be collected and disposed of responsibly. The requirements differ depending on the size of the operation. Generally, wastewater from livestock operations is collected in sewage lagoons, which are not very efﬁcient and often emit noxious odours. Land-based disposal systems, where stormwater run-off from the pens and process water is collected and then sprayed over a large, vegetated land area, are effective (Figure 10.11), but sometimes not permitted if the water table is high or the soil highly permeable. The depth of the sprayed efﬂuent is controlled by federal regulations to protect groundwater from contamination. Of course, if efﬂuent saturated soils receive rainstorms, this could result in contaminated run-off. If a large land area is not available, then other nutrient removal measures are necessary.
Horizontal subsurface flow treating dairy wastewater A Vermont, USA, study demonstrates that horizontal subsurface ﬂow wetlands are effective for achieving secondary quality efﬂuent from dairy stormwater run-off from
INCREASING THE SUSTAINABILITY OF AGRICULTURE 245 Figure 10.11 Sheet flow of stormwater across the feedlot pen is collected in a swale to allow solids to settle out. In this case, the water is then sprayed on adjacent pastureland. Photo: Stephen Ausmus, USDA. License: public domain.
Figure 10.12 Diagram of the treatment sequence for a Vermont dairy. A – Inflow from feedlot catch basin; B – Settling pond; C – Screened outlet; D – Two settling tanks; E – Inflow from milking parlour; F – Settling tank; G – Settling tank; H – Mixing and dosing tank; I – Horizontal subsurface flow wetland; J – Disposal tank. Image: Gary Austin after Tunçsiper (Pelissari et al., 2014).
pens and wastewater from the milking parlour. This is signiﬁcant as Vermont experiences very cold winters, making treatment in open water wetlands limited. Over a 4-year period, the dairy tested the performance of four constructed wetland cells: one vegetated (Scirpus ﬂuviatilis, river bulrush) and aerated, one vegetated and not aerated, one not vegetated and aerated, and one not vegetated and not aerated. Each cell was 2,422 square feet (225 m2) and 24 inches deep (60 cm). All cells featured 2-cm diameter gravel for the ﬁrst one-third of their length and 1-cm diameter gravel for the remainder. The vegetated and aerated cell produced slightly better water quality than the other cells. Figure 10.12 illustrates that stormwater run-off from the outdoor pens was collected in a catch basin and directed to a lagoon for sedimentation. After
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the lagoon, the stormwater was screened and directed to two settling tanks in series before ﬂowing into a tank where it joined wastewater from the milking parlour. The wastewater from the milking parlour was directed to a settling tank and then to the common tank (Tunçsiper, Drizo and Twohig, 2015). The combined wastewater was directed to the wetland. The wetland cells were designed to contain the 2-year 24-hour storm volume (37.5 m3). The hydraulic loading rate was between 10.44 and 14.42 cm per day, which is higher than common. The organic loading rate varied widely but averaged 0.21 kg per m2, which is much higher than common. Despite the high organic load, the wetland cells produced no clogging symptoms during the 4-year study. The inﬂow varied greatly between 132 and 2,642 gallons (500–10,000 litres) per day, depending on the weather and the milking parlour operation. The hydraulic residence time varied from 3 to 60 days depending on the inﬂow rate. The long resting periods may be important for the removal of organic material and may account for the capacity of the wetland to tolerate high organic loading rates at other times. The four cells operated in parallel. Aeration improved the performance of the cells. Performance also improved over time with the fourth year demonstrating the highest removal of BOD and TSS. The vegetated and aerated cell removed 86 per cent and 94 per cent of the BOD and TSS, respectively. The water entering this cell had an extraordinarily high average BOD concentration of 2,445 mg/L, which was reduced by the wetland to 278 mg/L. The initial TSS concentration was 829 mg/L, which was reduced to 40 mg/L (Tunçsiper, Drizo and Twohig, 2015). Although the BOD removal percentage is fairly high, the 278 mg/L average concentration is far above the 30 mg/L maximum permitted for discharge by municipal wastewater treatment plants. When the wetlands were operated in a two-stage sequence, performance also increased. BOD removal increased by 12 per cent and TSS removal increased by 16 per cent with two cells in series. This experiment demonstrates the outstanding treatment capability of horizontal ﬂow constructed wetlands in a cold climate. The performance of the wetland varied only slightly between winter and summer seasons. The wetland cells were covered with a layer of mulch to insulate them in winter. While BOD and TSS are basic indirect measures of water quality, excess ammonia, nitrate and phosphorus might still overwhelm receiving waters. The vegetated cells were much more effective in capturing phosphorus than cells with no vegetation. The wetland cell that was planted and aerated removed an average of 48.4 per cent of dissolved reactive phosphorus. This was 2.4 times more than the cell that was not aerated but planted. During the ﬁrst 21⁄2 years of operation, the treatment wetlands showed high efﬁciency in dairy efﬂuent treatment. The efﬂuent from the four horizontal ﬂow wetlands showed a 75 per cent average reduction in organic matter, 90 per cent in TSS, 90–99 per cent in E. coli and 80 per cent in ammonium (Tunçsiper, Drizo and Twohig, 2015).
Comparison of horizontal and vertical flow wetlands for dairy wastewater treatment As both nitrate and ammonia are generally high in feedlot and dairy wastewater efﬂuent, constructing a hybrid wetland should lead to better tertiary treatment results. A study in Brazil collected dairy wastewater from the milking parlour. It received primary treatment in a pond. A horizontal subsurface ﬂow wetland and a vertical
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subsurface ﬂow wetland, operating in parallel, allowed assessment of the treatment performance of each wetland type. The inﬂow to the wetland was high in nitrogen particularly ammonia: organic nitrogen and ammonia – 69 mg/L, ammonia – 55 mg/L and nitrate – 5 mg/L. The efﬂuent concentrations were consistent with the expected performance of each wetland type. The vertical ﬂow wetland removed more ammonia than the horizontal ﬂow wetland. Conversely, the horizontal ﬂow wetland removed more nitrate than the vertical ﬂow system. This conﬁrms that a two-stage treatment system with the ﬁrst stage using the vertical ﬂow distribution to convert ammonia to nitrate and a second horizontal ﬂow stage to convert the nitrate to nitrogen gas would be more effective for reducing all species of nitrogen (Pelissari et al., 2014). In order to reduce nitrate in efﬂuent from feedlot and dairy operations, a denitrifying wetland can be included in the treatment sequence to form a hybrid wetland. An example of this is a denitrifying wetland constructed on a dairy farm in Dargaville, New Zealand. Wash water from the dairy building and stormwater from outdoor pens ﬂowed to a lagoon and were then treated in a membrane biological reactor. After this secondary treatment (converting organic nitrogen and ammonia to nitrate), the water was treated in the denitrifying wetland. The carbon source was 50 per cent wood chips and 50 per cent sawdust from Pinus radiata. The wetland received an annual load of 68 pounds (31 kg) of nitrogen. The hydraulic ﬂow rate varied greatly and the total nitrogen was as high as 250 g of nitrogen/m3 of ﬁlter material. The amount of nitrate was as high as 200 g/m3 but was generally below 100 g/m3. The outﬂow from the wetland contained less than 1 g/m3 of nitrate. As expected, the denitrifying wetland did not reduce the amount of ammonia or organic nitrogen (Schipper, Cameron and Warneke, 2010).
Removal of endocrine disruptors by constructed wetlands Endocrine-disrupting compounds from dairies are signiﬁcant pollutants that can impact ecosystem and human health when discharged into the water supply. The 2.2 million dairy cattle in Britain excrete three times more oestrogen than the human population of 59 million. Free water surface wetlands treating dairy wastewater effectively remove endocrine-disrupting pharmaceuticals. One study demonstrated that 95.2 per cent of oestrogen hormones and 92.1 per cent of androgen hormones were removed by a free water surface treatment wetland at a dairy (Cai et al., 2012). A test of a hybrid treatment wetland (vertical subsurface ﬂow, horizontal subsurface ﬂow and free water surface cells operated in series) treating human wastewater revealed high removal of oestrogen and antimicrobial substances (Ávila et al., 2014). This sequence might also be applied to agricultural wastewater where animals receive regular doses of hormones and antibiotics.
Swine wastewater treatment with a vertical flow constructed wetland The Iowa Beef Nutrition Farm discussed earlier included a vertical subsurface ﬂow wetland. This example of a swine facility uses a composting step but also a vertical subsurface ﬂow wetland applied to the treatment of efﬂuent from swine. Vertical subsurface ﬂow wetlands have also been used to treat wastewater from concentrated chicken farms producing eggs. The swine application is interesting because a manure
248 INCREASING THE SUSTAINABILITY OF AGRICULTURE Figure 10.13 A – Manure slurry; B – Compost of manure and poplar wood chips (1:2) in two rows; C – Two leachate tanks, one for each compost row; D – Recirculation and dosing tank; E – Vertical flow wetland; F – Recirculation; G – Effluent discharge. Image: Gary Austin after Vazquez (Vázquez et al., 2013).
composting facility generates the wastewater and the wetland includes a recirculation feature in order to dilute the inﬂow with treated efﬂuent (Figure 10.13) (Vázquez et al., 2013). The vertical ﬂow wetland was a fairly standard design planted with Phragmites. The wetland received 360 litres of water from the recirculation tank every 6 hours for a hydraulic loading rate of 240 mm per day. The recirculation tank received a dose (100–300 L) of compost leachate once each week. The concentrations of nitrogen in the compost leachate were high (459 mg/L of NH3, and 904 mg/L of TKN). Unfortunately, the concentration of TSS was also very high at more than 3,000 mg/L during some operating periods. When the areal loading rates in grams per m2 per day were 9.2 – TSS, 17.9 – total COD, 4.8 – BOD and 1.9 – TN, the concentrations were reduced by more than 93 per cent by the vertical ﬂow constructed wetland (Vázquez et al., 2013). This study lasted 200 days, and the performance of the wetland varied during that period with respect to ammonia and nitrate removal. Initially, the nitrate concentration in the wetland efﬂuent was extraordinarily high at 178 mg/L, but after the wetland matured, the concentration dropped to 10 mg/L. Both nitriﬁcation and denitriﬁcation occurred, since the ammonia concentration was 16 mg/L during the last part of the testing period. This suggests that the wetland developed regions of anoxic conditions in, at least, portions of the weekly treatment cycle. Generally, vertical ﬂow constructed wetlands are characterized by high oxygen levels. Since a sedimentation basin or other pretreatment step to remove some TSS and nitrogen did not precede this wetland, the long-term performance is uncertain. The potential for clogging or reduction in the areal application rate is likely. A more deliberate design for TSS removal in pretreatment and for nitriﬁcation in the upper portion of the bed and a denitriﬁcation ﬂooded sub-basin, as presented in the chapter on vertical ﬂow constructed wetlands, might lead to more stable long-term performance (Vázquez et al., 2013).
Application of constructed wetlands in aquaculture operations The commercial production of ﬁsh and shrimp generate efﬂuent that is high in excess nutrients. As the concern for the health of streams and rivers has grown, regulations requiring treatment have been enacted. Systems are being developed where ﬁsh and plant production contribute to an efﬁcient use of nutrients and water (Figure 10.14). Treatment of efﬂuent from ﬂow-through systems and treatment to allow recirculation
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of production water are options dependent on the species being farmed and availability of water. Trout and Salmon require very cold, clean water, so ﬂow-through treatment is most common, although treatment of sludge removed from growing or hatchery tanks are additional treatment circumstances. Other species are more tolerant of some contaminants and lower dissolved oxygen. Low concentrations of contaminants and great volumes of water characterize aquiculture efﬂuents, whether ﬂow-through or recirculation is adopted. The typical concentrations are: BOD5 – 15 mg/L, COD – 12 mg/L, ammonia – 1.3 mg/L and total phosphorus – 0.3 mg/L. Hydraulic loading varies from an aerial loading of only a few centimetres per day to more than 29 m. Consequently, the hydraulic residence time also ranges widely from 3 hours to 4 days (Vymazal, 2014). Generally, the highest hydraulic loading rates result in ineffective removal of nitrate, although removal of ammonia and nitrite might be acceptable for the culture of ﬁsh and shrimp (Figure 10.15).
Figure 10.14 Will Allen illustrates that tilapia production can be combined with plant production for a holistic approach to using excess nutrients in pond water to irrigate plants and improve water quality of the fish. Photo: Grifray. License: CC-BYSA 2.0.
Figure 10.15 Concentrated populations of fish can create low water quality in the rearing ponds. Catfish are somewhat more tolerant of poor water quality than many other species. Here, mature brood fish catfish are inspected in a fish farm at the Warmwater Aquaculture Research Unit in Stoneville, Mississippi. Photo: Les Torrans, USDA, Agricultural Research Service. License: government work product.
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There are generally two treatment goals. The ﬁrst is producing water quality high enough to produce optimal growth if the water is re-circulated. The second is complying with discharge regulations to protect the quality of receiving waters. Nitrite and ammonia are particularly toxic to ﬁsh, whereas they are more tolerant of higher nitrate and phosphorus concentrations. All of the types of constructed wetlands have been successfully applied to treatment of aquaculture wastes. Free water surface wetlands have been used to treat water from channel catﬁsh and salmon farms. Horizontal subsurface ﬂow wetlands have been used to treat efﬂuent from trout and tilapia farms, while vertical ﬂow wetlands have treated efﬂuent from tilapia production. Finally, several combinations of the wetland types have been conﬁgured as hybrid wetlands and applied to a range of species.
Hybrid wetland for tropical fish production Tropical aquaculture of ﬁsh for commercial markets is a potent source of point source of pollution. This is due to the weekly or daily (or even more frequent) discharge of the ﬁsh pond water to the rivers and streams. Production using this model adds about 47.3 kg of nitrogen to receiving water for every ton of catﬁsh produced. Using constructed wetlands to clean and recycle the production water has the potential to avoid the discharge of tens of thousands of tons of nitrogen into every river where aquaculture is signiﬁcant, as it is in Vietnam, China and many other countries (Konnerup, Koottatep and Brix, 2009). Fish waste, uneaten ﬁsh food and the growth of algae and phytoplankton generate large quantities of organic nitrogen, ammonia and nitrate. The use of hybrid wetlands to treat these pollutants is necessary to create the aerobic conditions for nitriﬁcation and the anoxic conditions for removal of nitrite and nitrate. Hybrid treatment wetlands make possible recirculation of pond water with water quality sufﬁcient for the rapid growth of ﬁsh species. In contrast to treating domestic wastewater, aquaculture efﬂuent has a low concentration of contaminants but a very high volume of water to be treated. Therefore, devising a treatment system with a high hydraulic loading rate is important to minimize the size of the treatment wetlands (Konnerup, Koottatep and Brix, 2009). A study in Vietnam established a lined ﬁsh pond 8 by 8 m and 1 m deep, resulting in a volume of 40 m3. The pond was stocked with 15 km of Tilapia (125 km were harvested after 41⁄2 months). Two horizontal subsurface ﬂow wetlands operating in parallel and two vertical ﬂow subsurface wetlands operating in parallel composed the treatment system. The horizontal wetlands were 3.7 m long, 0.85 m wide and 0.3 m deep. They were ﬁlled with gravel (30–50 mm diameter) and planted Canna generalis. The vertical ﬂow wetlands were 1.25 m in diameter and 0.6 m deep, and planted with Canna generalis. The layers of gravel, from top to bottom, in this wetland were: a 0.2 m depth of 10–20 mm diameter gravel, a 0.4 m depth of 20–50 mm diameter gravel and a 0.1 m depth of 50–100 mm diameter gravel. The vertical ﬂow wetland received pulses of water for 30 seconds followed by a 2–10-minute resting period. The horizontal ﬂow wetland received water continuously (Konnerup, Koottatep and Brix, 2009). The treatment system was operated at hydraulic loading rates of 750, 1,500 and 3,000 mm per day. The highest loading rate yielded adequate water quality for ﬁsh production. At the 3,000 mm/day loading rate, dissolved oxygen was greater than
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1 mg/L, BOD was less than 30 mg/L, total ammonia was less than 1 mg/L and nitrite was less than 0.07 mg/L. The wetlands reduced BOD by 50 per cent, but the primary concern was the concentration of ammonia and nitrite. The toxic limit of nitrite for Tilapia is 0.5 mg/L compared to 0.07 mg/L produced by the wetland system. Ammonia is also toxic to Tilapia but the concentration produced by the treatment wetlands was well below harmful levels (Konnerup, Koottatep and Brix, 2009). As expected, the horizontal ﬂow wetlands removed more nitrate, while the vertical ﬂow wetlands removed more ammonia. Performance was the same in the wetlands for total nitrogen, nitrite, total phosphorus and phosphate, although all of these increased in concentration with increases in the hydraulic loading rate. Dissolved oxygen was 2–4 mg/L in the efﬂuent from the horizontal ﬂow wetland and 5.3– 6.1mg/L for the vertical ﬂow wetland (Konnerup, Koottatep and Brix, 2009). The hydraulic loading rate of this system is many times greater than in previous aquaculture operations. The high loading rate minimizes the land used and the construction cost of the treatment wetland. However, the high hydraulic loading rate did result in a steady increase in nitrogen and phosphorus over time. Most of the nitrogen increase was organic nitrogen rather than ammonia or nitrate. Nevertheless, the water quality was sufﬁcient for ﬁsh production. The design and performance of the treatment system would be improved by the inclusion of a settling tank to capture algae and particles. This would protect the wetland ﬁlter media from clogging problems. Algae grew rapidly in the pond and 45 species were identiﬁed. The algae caused high dissolved oxygen (12–13 mg/L) in the pond during the day but low levels (as low as 1 mg/L) at night (Konnerup, Koottatep and Brix, 2009). Signiﬁcantly, there was no discharge of polluted water during the 41⁄2-month dry season. Water was discharged only during the heavy rains of the wet season. If widely adopted, the use of constructed wetland would transform aquaculture from an unsustainable and damaging agricultural model to a sustainable one (Konnerup, Koottatep and Brix, 2009).
Hybrid wetland for tropical shrimp production Shrimp aquaculture is another opportunity for high rate recirculation of production water to establish a sustainable aquaculture industry. In this example, the hybrid wetland is composed of a free water surface wetland and a horizontal subsurface ﬂow wetland. The efﬁciency of this sequence allowed a much higher hydraulic loading rate than common, as it did in the hybrid wetland in Vietnam. In this case, the size of the treatment wetland was 43 per cent of the size of the production pond, compared to previous designs for shrimp aquaculture where the wetlands occupied 70–270 per cent of the pond area. A sedimentation cell before the free water surface wetland is an important component of the treatment system, and the horizontal ﬂow wetland showed no clogging symptoms. The hydraulic loading rate in the wetlands is 1.95 m per day, and the hydraulic residence time is 3 days. The treatment wetland reduced BOD from 7.1 to 2.5 mg/L, total ammonia from 0.18 to 0.06 mg/L and nitrite from 0.25 to 0.06 mg/L. However, nitrate increased to 40.1 mg/L and phosphorus increased to 3.8 mg/L. The concentration of nitrate and phosphorus was much lower when the hydraulic loading rate was 1.54 m per day rather than 1.95 m per day (Lin et al., 2005).
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Horizontal wetland for trout production The production of trout or salmon for commercial sale or in hatcheries for release to natural streams and rivers differs from ﬁsh production in tropical climates. Trout and salmon require very clean, cold water to ﬂourish (Figure 10.16). An example of a trout farm with a ﬂow-through system in Germany illustrates the application of a horizontal subsurface ﬂow constructed wetland to treat process water and efﬂuent from tank cleaning. The wetlands were conversions of six previously existing concrete sedimentation basins. These were divided into a sedimentation area and a wetland treatment area. The gravel (4–8 mm grain size) wetland was 1 m deep with Phragmites communis and Phalaris arundinacea equally dominant. The hydraulic loading rate during the cleaning operations was very high at 13.6 m per day and the wetland removed 68 per cent of the TSS. During normal operation, the hydraulic loading rate was 10.6 m per day and the total ammonia removal was 88 per cent. The subsurface wetland proved to be a better treatment solution than the previous sedimentation system for BOD, TSS, ammonia and nitrite, but nitrate removal was modestly higher in the sedimentation basin and phosphate concentrations were unchanged. The high nitrate concentration was due, in part, to their high concentration in the spring water feeding the farm.
Conclusion This chapter demonstrated that low-cost and reliable constructed wetland solutions are available, leading to substantial improvement in efﬂuent water quality from crop, livestock and aquaculture operations. Although these biological solutions will often lack the recreation beneﬁts of constructed wetlands in urban areas, they can greatly improve ecosystem health and availability of wildlife habitat. This is important, given the history of habitat destruction by agricultural development. Concentrating on the possible secondary beneﬁts, such as the harvesting of reed canary grass for cattle feed as in the Red River Station example, reduces the economic cost of creating treatment
Figure 10.16 Trout farms are often situated to allow water routed from streams to flow through the rearing raceways. The concentrated populations of fish produce waste and uneaten food that produce excess nutrients that can cause eutrophication downstream. Photo: Alejandro Linares Garcia. License: CC-BY-SA-4.0.
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wetlands. Excess nutrients in agricultural efﬂuent are actually resources that could be utilized to the beneﬁt of the enterprise if more holistic planning were to be implemented. Linking ﬁsh production to plant production is only the ﬁrst of these opportunities.
References Ávila, C., Matamoros, V., Reyes-Contreras, C., Piña, B., Casado, M., Mita, L., Rivetti, C., Barata, C., García, J. and Bayona, J. M. “Attenuation of emerging organic contaminants in a hybrid constructed wetland system under different hydraulic loading rates and their associated toxicological effects in wastewater,” Science of the Total Environment, vol. 470–471, pp. 1272–1280, February 2014. Cai, K., Elliott, C. T., Phillips, D. H., Scippo, M. L., Muller, M. and Connolly, L. “Treatment of estrogens and androgens in dairy wastewater by a constructed wetland system,” Water Resources, vol. 46, no. 7, pp. 2333–2343, May 2012. Haunschild, K., Leverenz, H. L. and Darby, J. Development of design criteria for denitrifying treatment wetlands WERF Report DEC13U06. Alexandria, VA: WERF, 2010. Jeong, C., Girouard, E. and Colyer, P. “Tailwater recovery system as a best management practice to improve irrigation water quantity and quality in Louisiana,” Presented at the 9th Louisiana Water Conference, Alexandria, Louisiana, 2015. Konnerup, D., Koottatep, T. and Brix, H. “Treatment of domestic wastewater in tropical, subsurface ﬂow constructed wetlands planted with Canna and Heliconia,” Ecological Engineering, vol. 35, no. 2, pp. 248–257, February 2009. Lin, Y. F., Jing, S. R., Lee, D. Y., Chang, Y.-F., Chen, Y.-M. and Shih, K.-C. “Performance of a constructed wetland treating intensive shrimp aquaculture wastewater under high hydraulic loading rate,” Environmental Pollution, vol. 134, no. 3, pp. 411–421, April 2005. Lizotte, R. E., Shields, F. D., Murdock, J. N., Kröger, R. and Knight, S. S. “Mitigating agrichemicals from an artiﬁcial run-off event using a managed riverine wetland,” Science of the Total Environment, vol. 427–428, pp. 373–381, June 2012. Lorimor, J. “An inﬁltration and wetland system to treat beef feedlot run-off,” Iowa State University, Department of Agricultural and Biosystems Engineering, Ames Iowa, 2003. Mee, L. “Reviving dead zones,” Scientiﬁc American, vol. 295, no. 5, pp. 78–85, November 2006. Millhollon, E. P. and Dans, D. R. “Using constructed wetlands to protect Louisiana waterways,” Louisiana Agriculture, vol. 53, no. 1, pp. 10–11, 30, 2010. Pelissari, C., Sezerino, P. H., Decezaro, S. T., Wolff, D. B., Bento, A. P., Junior, O. de C. and Philippi, L. S. “Nitrogen transformation in horizontal and vertical ﬂow constructed wetlands applied for dairy cattle wastewater treatment in southern Brazil,” Ecological Engineering, vol. 73, pp. 307–310, December 2014. Schipper, L. A., Cameron, S. C. and Warneke, S. “Nitrate removal from three different efﬂuents using large-scale denitriﬁcation beds,” Ecological Engineering, vol. 36, no. 11, pp. 1552–1557, November 2010. Schipper, L. A., Robertson, W. D., Gold, A. J., Jaynes, D. B. and Cameron, S. C. “Denitrifying bioreactors – An approach for reducing nitrate loads to receiving waters,” Ecological Engineering, vol. 36, no. 11, pp. 1532–1543, 2010. Tunçsiper, B., Drizo, A. and Twohig, E. “Constructed wetlands as a potential management practice for cold climate dairy efﬂuent treatment – VT, USA,” CATENA, vol. 135, pp. 184–192, December 2015. Vázquez, M. A., de la Varga, D., Plana, R. and Soto, M. “Vertical ﬂow constructed wetland treating high strength wastewater from swine slurry composting,” Ecological Engineering, vol. 50, pp. 37–43, January 2013. Vymazal, J. “Constructed wetlands for treatment of industrial wastewaters: A review,” Ecological Engineering, vol. 73, pp. 724–751, December 2014.
11 Treatment of industrial efﬂuent in constructed wetlands Introduction The concentrations of contaminants in industrial wastewater are generally so high that some form of pretreatment, such as anaerobic digestion, is necessary. Although still above acceptable discharge levels, most contaminants can then be reduced in constructed wetlands to meet regulatory standards. This treatment sequence, or even one that includes a secondary treatment process, is often an economic alternative to conventional treatment technologies. Wastewater from beverage and food processing, manufacturing, pulp and paper mills, petroleum reﬁneries and other industrial enterprises differ in content and concentration from municipal sewage or stormwater. Each industrial sector presents a different set of treatment challenges. A certain group of industries produce highly biodegradable waste. These include alcohol fermentation (distilleries, wineries and breweries), food processing (potatoes, milk, cheese and olives,) sugar reﬁneries (cane and beets), ﬁsh processing, meat processing and slaughterhouses. A general measure of biodegradability is the initial wastewater ratio of biological oxygen demand (BOD) to chemical oxygen demand (COD). When BOD/COD is more than 0.5, then the wastewater is considered easily biodegradable. For the industries listed above, the BOD/COD ratio ranges from 0.6 to 0.8. A second group of industries produce wastewater that is less biodegradable. These include the petrochemical, pulp and paper, and a range of other manufacturing industries (Vymazal, 2014). Various constructed wetland types are used to treat all of these efﬂuent types. Horizontal subsurface ﬂow wetlands are most frequently implemented due to their capacity to tolerate high organic loading, treatment of efﬂuent colour and where anoxic conditions are necessary to degrade contaminants. Vertical subsurface ﬂow constructed wetlands are necessary where aerobic conditions are necessary, such as in the conversion of ammonia to nitrate. Free water surface wetlands are effective for efﬂuent high in suspended solids, oil and grease (Wu et al., 2015). The examples of constructed wetlands offered below illustrate sustainable development, ﬁrst, because they treat wastewater on-site rather than deferring this to another time or pushing the pollution downstream. Second, the wetlands offer secondary beneﬁts not normally associated with industrial enterprises. Third, they are economical to operate.
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Petroleum industry Crude oil, natural gas and oil sand processing generate wastewater containing organic compounds, oil and grease, suspended solids, phenols, hydrogen sulphides, salts and metals. The hydrocarbons present in the efﬂuent include BTEX (benzene, toluene, ethylbenzene and xylenes), gasoline and diesel organic compounds. Total petroleum hydrocarbons are a common measure of contaminants from petroleum reﬁning operations (Vymazal, 2014). The concentration and type of contaminant varies greatly depending on the industry sector and reﬁning process. There are many examples of free water surface and horizontal subsurface ﬂow wetlands used to treat petroleum efﬂuent, but often a hybrid system is employed. For example, a treatment sequence of an aeration cascade, a free water surface wetland (1.5 acres, 0.6 hectares) and a horizontal subsurface ﬂow wetland (3.2 acres, 1.3 hectares) has been used in Casper, Wyoming, since 2008 to treat groundwater contaminated from eight decades of petroleum reﬁning activities (Figure 11.1). The hybrid wetland treats about 700,000 gallons of groundwater per day and reduces benzene (170 m/L), BTEX (470 m/L) and gasoline-derived organics (2,020 m/L) to below detection levels (Wallace, Schmidt and Agency, 2011). This case is especially noteworthy, as it is located on a golf course and business park redeveloped on the brownﬁeld of the previous petroleum reﬁnery. The free water surface wetland is planted with cattail and bulrush, and allows iron to precipitate after it has been oxidized in the belowground aeration cascade. The cascade is within a pipe embedded in a hillside slope. The wetland pools with their lush vegetation become part of the beautifully landscaped golf course (Figure 11.2). The horizontal subsurface ﬂow wetland includes a forced aeration system and is insulated by a 6-inch layer (15 cm) of wood mulch to prevent the water in the ﬁlter media from freezing in the very cold (to –31°F, –35°C) winters. The horizontal ﬂow wetland is planted with a variety of wetland species (Figure 11.3) (Wallace, Schmidt and Agency, 2011). It is expected to take at least 50 years to remove the estimated 30 million gallons of hydrocarbons that leached into the aquifer during the operation of the reﬁnery. The constructed wetland cost $3.4 million, but compared to other treatment options it saved $12.5 million in construction cost and will result in an additional $15.7 million in operating cost savings over the course of the remediation project (Natural Systems Utilities, 2015).
Figure 11.1 The treatment wetlands are embedded within the golf course in Casper, Wyoming. The free water surface wetlands are along the bottom and left of the image, while the round shapes at the top are the aerated horizontal subsurface flow wetlands. Photo: Google Earth, 42°50′21.00″ N 106°21′14.90″ W, image date: 17 August 2012, image accessed: 15 July 2015.
256 TREATMENT OF INDUSTRIAL EFFLUENT Figure 11.2 This groundwater remediation project in Casper is embedded within a Robert Trent Jones golf course. The difficulty and cost of cleaning polluted groundwater is higher than treating industrial wastewater on-site, before it contaminates the environment. However, this project allowed sustainable redevelopment to occur on this brownfield site. Photos: Gary Austin, 2015.
Figure 11.3 The horizontal subsurface flow wetland (with aeration and mulch insulation) is the last treatment step in the hydrocarbon removal project in Casper, Wyoming. Photos: Gary Austin, 2015.
An oil reﬁnery in Mandan, North Dakota, uses a lagoon, free water surface wetlands and vegetated swales to treat its industrial wastewater and to enhance wildlife habitat (Figure 11.4). The plant uses 1,500,000 gallons (5,700,000 litres) of water from the Missouri River each day for process purposes. After use, the contaminated wastewater ﬂows from an oil/water separator to an aerated lagoon and then through a series of six ponds and vegetated swales. Five additional ponds (47 acres, 19.1 hectares) are used infrequently for storage after heavy rainstorms or snowstorms or diversions from the primary ponds when a water quality problem is encountered. The ﬂexibility to bring the additional ﬁve ponds into the treatment sequence prevents water quality permit violations when water is discharged into the river. The additional ponds are managed for wildlife beneﬁt, primarily, but are needed as pollution control since stormwater run-off is not separated from process wastewater.
TREATMENT OF INDUSTRIAL EFFLUENT 257 Figure 11.4 Mandan refinery sequence of ponds and swales assures water quality compliance while providing excellent wildlife habitat through revegetation and creation of nesting islands. Photo: Google Earth. 46°51′28.92″ N 100°53′10.04″ W, image date: 15 September 2014, image accessed: 14 July 2015.
Nesting islands were constructed within the ponds and 50,000 trees and shrubs were planted. This resulted in 184 species of plants. Houses and feeders for ducks, swallows and purple martins were installed. The ponds were stocked with ﬁsh, which have been monitored and reveal no health problems. The state ﬁsh and game department has released Giant Canada Geese and the rearing of goslings has been successful at the site. Of the 191 bird species identiﬁed using the project area, 51 species nest there. Deer, fox, badger, skunk and raccoons are now common. In fact, the project received an award from the National Wildlife Federation, demonstrating a sustainable development conﬁguration (Baker and Schatz, 1989). The free water surface system at the Mandan reﬁnery effectively reduces BOD (98 per cent), COD (93 per cent), ammonia (84 per cent), sulphides (100 per cent), phenols (99 per cent) and oils and grease (99 per cent) in the wastewater. The hydraulic loading rate is 1.2 cm per day (Vymazal, 2014). A 0.5 mile (0.8 km) vegetated canal connecting the initial lagoon to the ﬁrst pond is responsible for most of the reduction of heavy metals in the wastewater (Baker and Schatz, 1989). Another example of the effective use of constructed wetlands for the sustainable development and operation of petroleum industry facilities is in Oman. The free water surface constructed wetlands in Oman are possibly the largest commercial treatment wetlands in the world (Figure 11.5). Here 1,433 acres (360 hectares) and an equal area of evaporation ponds are used to remove hydrocarbon from oil ﬁeld production water. When the Oman environmental protection agency enacted regulations prohibiting the injection of oil production wastewater into the shallow aquifer, the oil industry sought alternatives to the energy-intensive option of injection into the deep aquifer. The constructed wetland alternative requires only 2 per cent of the energy required by deep injection. Each day, the wetlands receive over 25 million gallons (95,000 m3) of water after residual oil is removed in an oil/water separator (Figure 11.6). More than 2 million Phragmites plants were planted in the wetland cells. The wetlands reduce the hydrocarbon concentration to less than 0.5 mg/L. The secondary beneﬁts of the project are oil recovery, the avoided cost of deep injection, generation of a commercially viable salt industry and bird habitat used by over 100 species. The large wetland is now an important resource for migratory birds
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Figure 11.5 Wastewater treatment wetland in Oman. Photo: Google Earth, 18°39′51.60″ N 55°47′14.08″ E, image date: 8 January 2015, image accessed: 17 July 2015.
Figure 11.6 Oman oil recovery and wastewater remediation. Photo: Courtesy of BAUER Group. www.bauer.de/en/ press/imagearchive/resources. html and www.bauer.de/en/bre/
(Figure 11.7). The low concentration of nitrogen and phosphorus and the high concentration of salt and boron content of the wastewater may be stressing the plants and may require the addition of artiﬁcial fertilizers in the future (Wu et al., 2015).
Wineries and breweries Winery efﬂuent is the result of crushing waste and washing equipment and bottles. The efﬂuents are characterized by intermittent ﬂow and variable contaminant
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Figure 11.7 The artificial wetland has become an important resource for resident and migratory bird species, Oman. Photo: Courtesy of BAUER Group, www.bauer.de/en/press/image_archive/resources.html and www.bauer.de/en/bre/.
concentration (Wu et al., 2015), but the wastewater includes alcohols. There is a large quantity of readily biodegradable organic matter in the wastewater, including sugars (glucose and fructose), alcohols (ethanol and glycerol), acids (tartaric, lactic and acetic) and suspended solids. However, there are also substances that are difﬁcult to degrade including polyphenols, tannins and lignin (Vymazal, 2014). Concentrations of COD at 5,000 mg/L or less allow the use of horizontal or vertical subsurface ﬂow wetlands for the treatment of winery wastewater. This concentration of COD is often exceeded, especially at large winery operations. Therefore, the raw wastewater must be diluted by recirculating a portion of the treated efﬂuent to bring the concentration of COD down from as much as 17,000 mg/L. Alternatively, the wastewater can be pretreated in various ways including anaerobic digestion before it enters the constructed wetlands (Wu et al., 2015). Horizontal subsurface ﬂow wetlands are most common in this industry due to their simple operation, but vertical subsurface ﬂow wetlands are also effective. Hybrid wetlands are necessary for advanced treatment and removal of the broadest range of contaminants and excess nutrients. An example of a constructed wetland for treatment of winery wastes is a system in Pontevedra, Spain. The treatment system included human wastewater from the associated agricultural tourism business as well as winery wastewater. The treatment sequence began with an anaerobic pretreatment step using a 1,585 gallon (6 m3) hydrolytic up-ﬂow sludge bed digester. The anaerobic step was primarily for the reduction of total suspended solids (TSS). The discharge from the digester went to a siphon tank and then to a 538 square feet (50 m2) vertical subsurface ﬂow wetland planted with Phragmites australis. Efﬂuent from the wetland was divided for ﬁnal treatment by three 1,076 square feet (100 m2) horizontal ﬂow constructed wetlands planted with Juncus effusus. Water entering the vertical ﬂow wetland contained TSS at 72–172 mg/L and BOD ranging from 216 and 1,379 mg/L and COD ranging between 422 and 2,178 mg/L. The average hydraulic loading rate was 19.5 mm per day, and the average organic loading rate was 30.4 grams of COD and 18.4 grams of BOD per m2 per day. Despite the high organic loading, the wetland performed well. The percentage removal for the contaminants was: 86.8 per cent TSS, 73.3 per cent COD, 74.2 per cent BOD5,
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52.4 per cent total Kjeldhal nitrogen ((TKN) organic nitrogen and ammonia), 55.4 per cent ammonia (NH3) and 17.4 per cent phosphates. As with winery efﬂuents, brewery wastewater has high concentrations of sugars, alcohol and suspended solids, but the pH is often very low (Vymazal, 2014).
Distilleries Spent wash water from distilleries is high in organic content (BOD: 35,000–60,000 mg/L; COD: 60,000–120,000 mg/L) and dark colour (Wu et al., 2015). The contaminants and unpleasant odour must be reduced before the efﬂuent is discharged into the environment. Generally, anaerobic reactors are used to treat the waste but aerobic processes have also been employed (Vymazal, 2014).
Potato processing Washing, peeling, slicing and precooking potatoes generates large quantities of wastewater high in starch and suspended solids. Constructed wetlands have been used to remove the highly biodegradable contaminants. Horizontal subsurface ﬂow wetlands and hybrid wetlands have been used to treat potato-processing wastewater. A hybrid wetland consisting of a sequence of free water surface (24.7 acres, 10 hectares), vertical subsurface ﬂow (9.8 acres, 4 hectares) and horizontal subsurface ﬂow (6 acres, 2 ha) wetland cells was designed to treat the wastewater (Wu et al., 2015). This approach was very successful in removing organic nitrogen (80 per cent removal), but ammonia (47 per cent removal) and nitrates remained in the discharged efﬂuent. However, this met the system goal and allowed the efﬂuent to be used for irrigation. A hybrid wetland in Japan successfully removed the following contaminants: COD (94 per cent removal), total nitrogen (90 per cent removal), ammonia (72 per cent removal) and total phosphorus (93 per cent removal). This system had three vertical subsurface ﬂow cells, a horizontal subsurface ﬂow cell and a ﬁnal vertical subsurface ﬂow cell in series (Vymazal, 2014).
Milking parlours and cheese production Efﬂuent from milk processing and cleaning contains high concentrations of COD, TSS and phosphorus, and oil and grease from milk solids (carbohydrates, proteins) and fat (Wu et al., 2015). Cheese whey is the wastewater that is generated when making cheese. It is composed of urea, uric, lactic and citric acids, lactose, proteins, lipids and mineral salts. These are combined with sterilization wash water and typically treated in an up-ﬂow sludge blanket reactor (Vymazal, 2014). The chapter on agricultural applications of constructed wetlands reported the performance of constructed wetlands treating dairy efﬂuent including milking parlour content.
Tanneries Processing animal skins with either tannins or chromium creates efﬂuents high in salts (as high as 80 grams of NaCl per litre), suspended solids, ammonia, organic nitrogen and chromium (up to 50 mg/L) or tannins (up to 3,000 mg/L) (Vymazal, 2014). In a study of horizontal subsurface ﬂow wetlands for the treatment of tannery wastewater,
TREATMENT OF INDUSTRIAL EFFLUENT 261 Table 11.1 Summary of tannery effluent treatment performance at the hydraulic loading rate of 6 cm per day and a hydraulic residency time of 7 days (Calheiros, Rangel and Castro, 2009)
COD BOD5 TSS TKN–N NH3–N TP
Concentration (mg/L) In
1,598 706 80 122 81 0.41
252 159 9 55 42 0.27
Loading (kg ha day)
83 77 88 54 48 38
479 212 24 37 24 0.09
404 164 21 20 13 0.04
inﬂuent levels of 420–1,000 mg/L of BOD were reduced as much as 88 per cent and 808–2,449 mg/L of COD were reduced as much as 92 per cent (Table 11.1). The treatment system began with wastewater collected in an equalization tank followed by a tank for coagulation, ﬂocculation and sedimentation. Then, the wastewater was delivered to two horizontal wetland cells operated in series and planted with Phragmites australis and Typha latifolia. Both species grew well in the wastewater, although the Phragmites became established and expanded more readily (Calheiros, Rangel and Castro, 2009). The study resulted in the recommendation of a maximum organic loading of 1,153 pounds per acre (212 kg per hectare) per day and a 7-day hydraulic retention time in order to meet tannery discharge standards (Portugal). The wetlands reduced sulphates by an average of 56 per cent and colour by an average of 60 per cent at a hydraulic loading rate of 6 cm per day and a hydraulic residence time of 7 days. Nitrate was reduced about 50 per cent, decreasing from 43 mg/L to 21–24 mg/L (Calheiros, Rangel and Castro, 2009).
Chemical and textile industry case study Chemical manufacturing companies produce wastewaters that vary greatly in toxicity and in the kind of contaminants. A 15-acre (6 hectare) hybrid wetland (Figure 11.8) to treat efﬂuent from chemical and textile manufacturing enterprises in the Changshu Advanced Materials Industrial Park in China was completed in 2014. Designed by Blumberg Engineers, the project is located in Changshu, Jiangsu Province. The wetland is designed to treat 1.1 million gallons (4,000 m3) of pretreated efﬂuent per day in order to protect the Yangtze River adjacent to the industrial development (Blumberg Engineers, 2014). The ﬁrst and largest stage of the hybrid treatment wetland is a vertical subsurface ﬂow wetland (Figure 11.9) (4.7 acres, 18,900 m2) arranged in a semicircle (Figure 11.8–A). The second treatment stage has three cells operated in a series. The ﬁrst cell is a deep pond (0.65 acres, 2,652 m2), and the second cell is an artiﬁcial rocky creek (0.3 acres, 1,064 m2) (Figure 11.8–B, C, D). The last cell is a shallow, free water surface wetland (1 acre, 4,019 m2). Stage three (Figure 11.10) consists of a horizontal subsurface ﬂow wetland (2.5 acres, 10,062 m2) (Blumberg Engineers, 2014). Although the inﬂow is pretreated, it remains highly polluted including high levels of salinity and ﬂuoride. The vertical subsurface ﬂow wetland transforms organic compounds and nitriﬁes the efﬂuent. The pond, stream cascade and shallow marsh
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Figure 11.8 The treatment wetland during construction. The hybrid wetland is composed of the arcs of the vertical flow stage (A), the pond, stream and marsh sequence to the left and bottom of the site. The horizontal subsurface flow stage (E) is shown on the right side of the image. In this image, the industrial context is clear, but new moderate density housing is also visible to the south. The Yangtze River is 1,000 feet (305 m) to the north. A – Vertical subsurface flow wetland; B – Pond; C – Rocky creek; D – Free water surface wetland; E – Horizontal subsurface flow wetland. Photo: Google Earth (CNES, Astrium), 31°46′48.30″ N 120°49′04.46″ E, image date: 11 December 2013, image accessed: 2 August 2015.
Figure 11.9 In this view toward the northeast, the first stage of the treatment wetland is organized as concentric bands of vertical flow subsurface wetland with a variety of plants. The industrial towers in the background include pretreatment of the process water, before it is distributed across the vertical flow wetland. Photo: Blumberg Engineers, www.blumberg-engineers.com.
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Figure 11.10 The horizontal subsurface wetlands feature Cattail (Typha). The visitor centre is visible in the background. The attractive design, wildlife habitat and visitor centre are valuable secondary benefits of the project. The reuse of wetland effluent by the chemical plants is another benefit that reduces the water demand of the factories. Photo: Blumberg Engineers, www.blumberg-engineers.com.
allow for precipitation and settling of phosphorus. In addition, the shallow marsh decreases COD levels. The horizontal ﬂow wetland is provided for denitriﬁcation and other anaerobic processes to improve the water quality. The design of the wetlands allows for recirculation and by-pass depending on the treatment needs (Blumberg Engineers, 2014). The advanced treatment of the industrial efﬂuent is necessary to protect the, already polluted, Yangtze River from further degradation. The proximity of the treatment wetlands to the river increases its value as replacement habitat for historical riverbank habitat losses.
Pulp and paper mills Wood pulping and paper production generates tremendous amounts of wastewater. Modern mills require about 3,400 gallons (13 m3) of water to produce one ton of paper (Kamali and Khodaparast, 2015). The wastewater is characterized by high concentrations of BOD and COD. A mechanical-chemical process can generate more than 7,000 mg/L of COD and 3,000 mg/L of BOD. Other contaminants include suspended solids, volatile organic compounds (terpens, phenols, chloroform and methanol), fatty acids, lignin, and adsorbable organic halogens or resins (Vymazal, 2014). Adsorbable organic compounds include as many as 500 different substances associated with the use of chlorine to bleach pulp and paper. Many of these compounds are not readily biodegradable. Which contaminants are contained in the wastewater is inﬂuenced by whether the pulping process is mechanical or mechanicalchemical. The chemical process uses chemicals such as sodium hydroxide and sodium sulphide. As many as 700 organic and inorganic contaminants may be present in the raw wastewater. Although all pulp and paper mills treat their efﬂuent, they remain one of the major sources of water pollution. The high concentration of contaminants requires pretreatment before the wastewater can be directed to constructed wetland for additional treatment. An
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anaerobic digester is often used as a pretreatment step, as this effectively removes organic material with little energy input and results in methane gas that can be used as an energy resource by the factory. Aerobic treatment, such as activated sludge technology, is also common. Physiochemical methods are emerging to address some of the most recalcitrant contaminants. Free water surface and horizontal subsurface ﬂow wetlands have been used to provide secondary or tertiary treatment of pulp and paper wastewater. A pilot horizontal subsurface ﬂow wetland demonstrated a reduction in COD from 1,083 to 98 mg/L with an 8.6-day hydraulic retention time. The colour of the efﬂuent was also dramatically reduced. The Canna indica planted in the wetland grew proliﬁcally (Choudhary et al., 2011). There are several process subsystems involved in the pulp and paper industry, some of which are well suited to wetland wastewater treatment. Two are the treatment of stormwater and the treatment of leachate from log and chip piles. Treating these efﬂuents separate from mill process water reduces the volume of water that must be accommodated by the systems that treat process water.
Thermoelectric power generation As noted in the ﬁrst chapter, the thermoelectric power generation industry in the United States uses more water than any other sector of the economy. Constructed wetlands allow the reuse of water by this industry after the water is treated. Thermoelectric power plants use about 90 per cent of their water for cooling, but also use water to manage and transport waste ash and to operate air pollution scrubbers. This section presents constructed wetlands that treat wastewater from a coal-ﬁred power plant air pollution reduction system. According to the US Environmental Protection Agency (EPA), pollutant discharges from the thermoelectric power industry are increasing in volume and total mass. Steam electric power plants are responsible for approximately 50–60 per cent of all toxic pollutants discharged into surface waters by all industries regulated under the Clean Water Act. A rule proposed by the US EPA would limit the concentration of toxic metals and nitrate in the efﬂuent from these energy plants (US Environmental Protection Agency, 2013). These metals can be removed from the wastewater by constructed wetlands.
Jeffrey Energy Centre case study Removing the air pollutants with the use of scrubbers creates contaminated wastewater that requires treatment before it can be discharged to the natural environment or reused. The Jeffrey Energy Centre near St Mary’s Kansas, USA, implemented air pollution scrubbers for the stacks of its coal-ﬁred power plant. This reduced sulphur dioxide emissions by 97 per cent (Reitenbach, 2014).
Constructed treatment wetland The wastewater from the air pollution scrubbers contains mercury, selenium, boron, ﬂuoride, sulphate and low levels of chlorine. A pilot and then full-scale wetlands (Figure 11.11) were constructed as the lowest cost treatment alternative to reduce these contaminants. Sulphate was not reduced sufﬁciently in the pilot wetland. Therefore, it was removed through a pretreatment precipitation process instead.
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Figure 11.11 Full-scale wetland treatment of effluent from a coal-burning power plant in Kansas. The foreground ponds are equalization ponds, the eight cells in the centre of the image are vertical subsurface up-flow wetlands and the upper two cells are horizontal subsurface flow wetlands. Photo: Google Earth 39°16′33.04″ N 96°07′50.87″ W, image accessed: 14 July 2015.
Table 11.2 Hybrid wetland and the removal of metals (Bland, Snider and Haag, 2014)
Mass load reduction (%)
Average influent (ug/L)
Average effluent (ug/L)
Mercury Selenium Boron Fluoride
83 92 42 93
1.2 114 3,459 11,209
40.0 m/s (>5.67 in/h)
≤40.0 to >10.0 m/s ≤10.0 to >1.0 m/s ≤1.0 m/s (≤5.67 to >1.42 in/h) (≤1.42 to >0.14 in/h) (≤0.14 in/h)
50 to 100 cm [20 to 40 in]
50 to 100 cm [20 to 40 in]
50 to 100 cm [20 to 40 in]
≤4.0 to >0.40 m/s ≤0.40 m/s (≤0.57 to >0.06 in/h) (≤0.06 in/h)
>100 cm [>40 in]
>100 cm [>40 in]
>100 cm [>40 in]
>100 cm [>40 in]
>100 cm [>40 in]
>100 cm [>40 in]
>100 cm [>40 in]
Depth to high water table >100 cm [>40 in]
For hydrologic soil groups where an impermeable layer is less than 100 cm (40 inches), see the table above.
276 APPENDIX C
Figure A.C.3 Soil texture classification Image USDA; license: US government work product.
Table A.C.7 Soil particle sizes
Very coarse sand Coarse sand Medium sand Fine sand Very fine sand Silt Clay
2.0–1.0 mm 1.0–0.5 mm 0.5–0.25 mm 0.25–0.10 mm 0.10–0.05 mm 0.05–0.002 mm < 0.002 mm
Table A.C.8 Soil infiltration rates
Soil texture, type
Soil texture, type
Coarse sand Medium sand Fine sand Loamy sand Sandy loam Fine sandy loam Very fine sandy loam
1.25 1.06 0.94 0.88 0.75 0.63 0.59
Loam Silt loam Silt Sandy clay Clay loam Silty clay Clay
0.54 0.50 0.44 0.31 0.25 0.19 0.13
Note: Rates based on full cover. These figures decrease with time and per cent of cover. Derived from USDA information. (SCC 0812 § 1, 1990.)
APPENDIX C 277 Table A.C.9 Plant species within the JEL Wade Wetland, Wilmington, North Carolina, USDA Hardiness Zone 7 (Mallin et al., 2012) Trees Carpinus caroliniana – ironwood – deciduous tree Cornus foemina – swamp dogwood – deciduous tree Nyssa biflora – swamp tupelo – deciduous tree Pinus palustris – longleaf pine – evergreen tree Quercus laurifolia – laurel oak – deciduous tree Quercus michauxii – swamp chestnut oak – deciduous tree Quercus virginiana – live oak – evergreen tree Taxodium distichum – bald cypress – deciduous tree Shrubs Alnus serrulata – smooth alder – deciduous shrub Crategus viridus – green hawthorn – deciduous tree Aronia arbutifolia – red chokeberry – deciduous shrub Cephalanthus occidentalis – buttonbush – deciduous shrub Chamaecyparis thyoides – swamp dogwood – deciduous shrub Cyrilla racemiflora – titi – evergreen shrub Ilex glabra – inkberry – evergreen shrub Ilex verticillata – common winterberry – deciduous shrub Itea virginica – Virginia sweet-spires – deciduous shrub Myrica cerifiera – wax myrtle – evergreen shrub Sambucus canadensis – common elderberry – deciduous shrub Viburum nudum – southern wild raisin – deciduous shrub Other Acorus calamus – sweet flag – grasslike Carex (species mix) – sedges Eupatorium – spp. semaphore thoroughwart – fleshy flowering herb Helianthus angustifolius – swamp sunflower – flowering herb Hibiscus moscheutus – rose mallow or marsh mallow – flowering herb Hibiscus coccineus – scarlet rose mallow – flowering herb Iris fulva – copper iris – flowering herb Iris virginica – southern blue flag – flowering herb Juncus coriaceous – leathery rush – rush Juncus effusus – soft rush – rush Kosteletskya virginica – seashore mallow – flowering herb Leersia oryzoides – rice cutgrass – grass Nuphar luteum – spatterdock – fleshy herb Peltandra virginica – arrow arum – fleshy herb Pontederia cordata – pickerelweed – fleshy herb Schoenoplectus tabernaemontani – softstem or great bulrush – sedge Sparganium americanum – eastern burr-reed – grass-like Saggitaria lancifolia – bull-tongue arrowhead – fleshy herb Saururus cernuus – lizard’s tail – flowering herb Veronia novaboracensis – New York ironweed – flowering herb Zizaniopsis miliacea – giant cutgrass – grass
278 APPENDIX C Table A.C.10 Bio-retention basin plants – Pacific Northwest, USA The plants below are suitable for the wet zone of bio-retention basins
Alnus rubra Fraxinus latifolia Malus fusca Salix Iucida
Red alder Oregon ash Pacific crabapple Pacific willow
Emergent plants Carex obnupta Carex stipata Juncus densifolius Juncus effuses Juncus tenuis Scirpus acutus Scirpus microcarpus
Slough sedge Sawbeak sedge Common rush Daggerleaf rush Slender rush Hardstem bulrush Small-fruited bulrush
Comus sericea Comus sericea ‘Kelseyi’ Comus sericea ‘flaviramea’ Comus sericea ‘Isanti’ Lonicera inuolucrata Myrica californica Physocarpus capitatus Rosa pisocarpa Salix purpunea ‘Nona’ Spiraea douglasii
Red-twig dogwood Dwarf dogwood Yellow dogwood Isanti dogwood Black twinberry Pacific wax myrtle Pacific ninebark Clustered Wild rose Dwarf Arctic willow Douglas spirea
References Dong Yue, Y., Zhang, Y., Liu, X., Li, Y., Jin, J., Duan, T., Li, J. and He, P. “Construction of ecosystem and water quality control of Houtan wetlands in Shanghai Expo Garden,” Wetland Science, vol. 3, pp. 219–226, 2013. Mallin, M. A., McAuliffe, J. A., McIver, M. R., Mayes, D. and Hanson, M. A. “High pollutant removal efﬁcacy of a large constructed wetland leads to receiving stream improvements,” Journal of Environmental Quality, vol. 41, no. 6, p. 2046, 2012. Reiners, J. “Vegetation growth and success as a function of soil moisture conditions in bioretention cells,” 2008. [Online]. Available: www.seattle.gov/util/cs/groups/public/@spu/ @usm/documents/webcontent/spu02_020010.pdf. [Accessed: 12 July 2016]. USDA (US Department of Agriculture), “Part 630 hydrology national engineering handbook,” US Department of Agriculture, 210–VI–NEH, 2007. USDA (US Department of Agriculture), “Urban Hydrology for Small Watersheds,” Technical Release 55, 1986. Vymazal, J. “Emergent plants used in free water surface constructed wetlands: A review,” Ecological Engineering, vol. 61, pp. 582–592, December 2013.
2,4-D 213, 214 absorbable organic compounds 263 Acetaminophen 92 acetic acid 259 Acorus gramineus 130 activated sludge 264 acute pollution level 17, 23 aerated horizontal subsurface wetland 255 aerated lagoon 30, 39–41 aerated pipes 72, 75, 90 aeration 245 aeration cascade 255 Agapanthus africanus 130 agriculture: commodities 233; four-stage wetland 242; horizontal subsurface wetland 244; hormones 247; land-based disposal 244; phosphorus 236; sewage lagoons 244; TSS 235; water 233 Albany, Oregon 41–43 alcohols 259 algae 251 algae bloom 20 alteration of rivers 144 aluminium polychloride 72 ammonia 45, 244, 247, 248, 251 anaerobic digestion 254, 264 androgen hormones 247 anoxic 29 aquaculture 248; goals 250; horizontal subsurface wetland 252; pond size 251; water use 250 aquifers, composition 13 aquifers, USA 13 arrowhead 119 Arroyo Secco River 144 artiﬁcial fertilizer 238 Arundo spp. 126 ATI Wah Chang 43
Atlanta, Georgia 189 atrazine 235 Austria 81 Azolla 43 Bacillus 83 background concentrations 47 Bacopa monnieri 132 acteria: colonies 23; measurement 23 base ﬂow 11, 214 Bayawan City, Philippines 64 Bay of Biscay, France 239 Beef Nutrition Farm 242 bentonite 36 benzene 255 biodegradability 254 biological oxygen demand 25, 245; test 26 biomass 80 bio-retention: bacteria 212; basins 205; design criteria 206; ﬁlter media 209; ﬂooded sub-basin 208; ﬂow sequence 207; hybrid 213; materials 209; PAH 212; plants 210, 213, 278; pretreatment 206; subgrade soil 208; treatment basin 206; under-drain 207; water management 210 Bird of paradise 130 Bisphenol A 92 Black Sea 238 Blue Heron Water Reclamation Facility 31, 33 Blumberg Engineering 77, 94. 96, 261 BOD 25, 245 BOD/COD ratio 254 Boone Presbyterian Church wetland 47 Boston 15 Brazil dairy wetland 246 broadleaf cattail 45 brownﬁeld 151, 168
BTEX 255 bugle lily 131 bulrush 114 cadmium 66 Calla lily 128 Caltha palustris 121 Canna generalis 250 Canna indica 264 Canna spp. 122–124 carbolic acid 149 cardinal ﬂower 47 Cares spp 116–118 Carex appressa 212 Carrion de los Cespedes 88 carrying capacity 19 Casper, Wyoming 255 catﬁsh 249 cattail 104 Center for New Water Technologies 89 centralized wastewater treatment 16 CH2M Hill 41 Changshu Advance Materials Industrial Park 261 Changshu, China 77 Charlotte, North Carolina 210 cheese production wastewater 260 chemical manufacturing wetlands 261 Chinese Pavilion 153 Chinese water quality: classes 156; standards 156 Chinook salmon 45 chlorine 263 chromium 260 chronic pollution level 17, 19, 23 Clayton County, Georgia 40 Clean Water Act 264 Cle Elum, Washington 39–41 Cleveland 16 climate change 11 climate change, Europe 12 climate change, USA 12 clogging 251 coal-ﬁred power plants 10, 149 Coldwater River, Mississippi, wetland 234–235; performance 237 cold weather wetlands 255 coliform bacteria 28 Colocasia esculenta 132 common reed 51, 106 Composite Curve Numbers 274, 275 concentrated animal operations 241
constructed wetlands: stages 22; stage sequences 22; types 21 contaminant concentration 22 conventional wastewater treatment plants 28 copper 66 corridors: ecological 2; stormwater 2, 7; width 2 Cuyahoga River 16 Cyperus alternifolius 38 Cyperus spp. 125 Czech Republic 50, 67 dairies 244; endocrine disruptors 247; wastewater 244 dairy wetland, performance 245 Danish system 72 Dargaville, New Zealand 247 dead zones 20, 238; map 240 decentralized wastewater treatment 16, 28 denitrifying wetland 45, 239–241, 247 Denmark 70 Denver, Colorado 11 Des Plains River wetland 142 dicamba 213, 214 Diclofenac 92 dissolved Oxygen 26 distilleries 260 distribution piping 72, 73 DO 26 Drosera burmanni 38 duckweed 135 ecological corridors 2; length 4; see also corridors ecosystem service, water 15 Eichhornia crassipes 38, 133–134 Eleocharis dulcis 112 Eleocharis fallax 112 Eleocharis palustris 111 Eleocharis sphacelata 112 Eleocharis spp. 110–112 E L Huie Jr Constructed Treatment Wetlands 39; performance 39 emergent vegetation 102 Endangered Species Act 9 Enterococci 28 Escherichia coli (E. coli) 23, 38–39, 91, 187; standard 28 ethanol 259 Ethinylestradiol 92 ethylbenzene 255
Experimental Wastewater Treatment Plant of Carrión de los Céspedes 61 facultative lagoon 29, 50 faecal coliform 66 feedlots 241 ﬁeld edge wetland 234 ﬁrst ﬂush 187 Flanders, Belgium 66 ﬂoating plants 43 ﬂood irrigation 10 ﬂow through cooling 10 food processing wastewater 254 free water surface wetland 21, 31, 38, 39, 41–43; aeration 33, 44; BOD 47; cell shape 35; clogging 37; cold weather 37; conﬁguration 34; depth 35; design challenge 32; ﬁlter media 37; ﬁsh 39; history 32; hydraulic loading 35; inﬂuent distribution 36; inlet 36; large scale 39; loading 34; materials 36; metals 47; Netherlands 32; nitrogen 47; Orlando, Florida 32; outlet 37; pathogenic bacteria 48; performance 47; phosphorus 47; plants 38; rural 40; secondary treatment 38; site scale 38; sizing 34; slopes 37; TSS 47; wildlife 47 fructose 259 gasoline-derived organics 255 geotextile fabric 202 Giant Canada Geese 257 glucose 259 glycerol 259 glyphosate 213, 214 grams 22 Greensborough, North Carolina 211 Greenworks 216 groundwater 12; contamination 255; nitrate 14; pollution 14 habitat, patch size 4 Hal Marshall: bio-retention basin 211; performance 212 Harbin, China 217 hardstem bulrush 40, 45 Heliconia spp. 95, 128 Hennersdorf, Germany 94 Hewletts Creek 192, 195 high density polyethylene 34 horizontal subsurface ﬂow constructed wetland 21; case study 61, 63, 64, 66,
67, 250, 260; cell shape 54; clogging 56–57; cold climate 67; conﬁguration 50; depth 55; design challenge 52; ﬁlter media 58–60; history 50; hydraulic loading 53; inlet 52, 58; liner 57; loading 52, 55; materials 57; metals 66; nitrogen 65; pathogenic bacteria 65; performance 63, 64, 65; phosphorus 65; planting design 136; plug ﬂow trench 61–63; pretreatment 55; residential 63; sizing 52–53 Houtan Park wetland, Shanghai 101; aeration 159; aquatic organisms 271; bamboo decking 164; biological 153, 155, 156, 159, 161, 170; case study 148; climate change adaptation 170; common aquatic organisms 154; common plants 154; context 151; cultural ecosystem services 162; diversity 170; economic impact 168; ecosystem services 169, 170; education 167; ﬁrst stage 157; ﬂood control 152; maintenance 168; pedestrian route 163–164; planting design 155; planting plan 158; program 154; program implementation 114; recycled steel 166; site art 165; stormwater 161; sustainability 168; terraces 159–162; treatment performance 155; water treatment sequence 154; wetland plants 172, 271 Huangpu River, Shanghai 148; water quality 151 Hubei, China 1 hybrid bio-retention basins 213 hybrid constructed wetlands, 22, 87, 250, 251, 260; agriculture 87; case study 88, 92, 93, 94; Changshu, China 262; E. coli 91; free water surface stage 90; horizontal ﬂow stage 90; loading 89, 93; performance 91; secondary beneﬁts 94; tertiary treatment 87; three-stage 93; vertical ﬂow stage 89 hydraulic loading 245, 248, 250, 252, 261 hydraulic residency time 36 hydrocarbon 207; removal 255, 257 hydrologic soil group criteria 275 Hygrophila pogonocalyx 38 Hymenocallis littoralis 132 hypoxic Zones 239 Ibuprofen 92 Imhoff tank 88
impaired waters 17, 19 industrial wastewater 254 industry: free water surface wetland 256, 257; horizontal subsurface wetland 260; hybrid wetland 255, 261, 265; liner 266; metals removal media 266; Phragmites 257, 259, 261; stormwater 256; Typha 261, 263; vegetated swales 256; water use 263; wetlands cost beneﬁt 266; wildlife 256 inﬁltration 11; requirements 214, 215 inundation levels 103 Iowa State University 242 Iris pseudacorus 63, 79, 80 Iris sibirica 63 Iris spp. 118–119 iron 66 irrigation water 9; efﬁciency 10 Isar River 145, 173
mercury 19 metals: contamination 264; removal 265 methane 76 Microccus 83 micrograms 23 milking parlor 245, 260 Millennium Ecosystem Assessment 142, 229 milligrams per litre 22 mining 19 Minnesota 67 Mississippi River 14, 20, 144, 239 Missouri River 256 mosquitos 39 most probable number (MPN) 23 Munich, Germany 145 municipal master planning 1
lactic acid 259 Lake Taihu 148 Lake Yangcheng 95 Las Vegas 15 lead 66 Lemna minor 135 Liang Zhi Hu Lake 2 Liaohe Delta, China 106 Liebenburg-Othfresen, Germany 50 liners 36 Long Beach, California 187 Los Angeles River 148 Lotus Island 95 Ludwigia adscendens 38
NaCl 260 Naphthalene 207 National Cheng-Kung University wetland 38 National Cheng-Kung University wetland, performance 38–39 National Urban Wetland Park 175, 217; basin sequence 220; context 217; design 219; economic development 236; ecosystem services 226; land-use 218; outlet 225; pavilions 226; site grading 214; water management 221; water treatment 223 New York City 142 nitrate 27, 45, 240, 244, 247, 248; for irrigation 260 Nitrobacter 83 nitrogen: ammonia 27, 45; in streams and rivers 17 Nitrosococcus 83 Nitrosolobus 83 Nitrosomonas 83 Nitrosopira 83 Nitrospina 83 non-point source pollution 20 Nuphar shimadai 38
Macropodus opercularis 39 Mandan wetland, North Dakota 256; performance 257 manure slurry 248 marsh marigold 121 measurement units 22 mechanical/chemical processing 263
Oaklands Park, England 92 oestrogen hormones 247 Ohio State University 213 oil recovery 256, 257 oil/water separator 257 Olympic College Parking Garden 178 Oman wetland 257
Jeffrey Energy Centre, case study 264 JEL Wade Park 192–197 JEL Wade wetland plant list 277 Juncus effusus 109, 259 Juncus spp. 108–110 Kobuk, Alaska wetlands 147 Krovi, Czech Republic 51 Kurisu International 41
Onion Creek 242 Oregon City 216 organic: loading 245, 261; pollutants 19 organic matter, transformation 27 oxidation 60 Oxybenzone 92 PAH 144, 150, 187 papyrus 80, 125 pathogens 28 permethrin (Hi Yield38) 235 personal care products 92, 93 pesticides 236; in streams 17 petrochemical 19 petroleum wastewater wetland 255 Phalaris arundinacea 65, 102–114, 252 pharmaceuticals 92, 93 phenol 149, 263 Philadelphia 1, 177 phosphorus 28, 212, 236, 244; in steams and rivers 17; wastewater 18 Phragmites australis 59, 81, 106 Phragmites communis 252 Phragmites karka 64, 106 Phragmites spp. 106–108 phytoplankton 239 Pickerel weed 121 Pistia stratiotes 135 plants 98; beneﬁts 80; common deep marsh 102; common marsh species 102; nutrient uptake 80; listed by continent 269; planting design 101, 103, 136; shallowest water 102 point source pollution 16 pollutant load 23 polycyclic aromatic hydrocarbons (PAH) see PAH polyvinyl chloride 36 Pontederia spp. 121 Pontevedra, Spain, wetland 259 population equivalent 25 Portland, Oregon 210 potato process wastewater wetland 260 precipitation 11 primary treatment 26 Prince George’s County, Maryland 215 Pseudomonas 83 pulp and paper mill, wastewater 263 pumping tank 72 Qinhuangdao City, China 174 Quanti Tray Sampler 23
rain garden 205 recirculation 83, 250 reclaimed water, piping 16 Red River Research Station, Louisiana 237; wetland: stages 237 redox potential 60 reduction 60 reed canary grass 112 Reinhold Kickuth 50 retroﬁtting 1 riparian wetlands 142; natural 146; vegetation 146 river: assessment 17, 19; channelization 148; pollution 16; restoration objectives 145 Rivers and streams, biological condition 18; Mediterranean river ﬂow 12 Roseburg Oregon 17–18 run-off: curve numbers 272; depth 274; urban 11; volume 11 rush 109 Sagittaria 119–121 Sagittaria latifolia 45 St May’s Kansas, USA 264 salmon 26, 249 Sanlihe River 143, 172 Schoenoplectus acutus 45 Schoenoplectus tabernaemontani 45 Scirpus acutus 40, 45 Scirpus ﬂuviatilis 245 Scirpus spp. (Schoenoplectus) 114–116 Scirpus validus 45 scrubbers 264 secondary treatment 26 sedimentation 19; cell 251 Seidle, Kathe 50, 70 septic tanks 76; septic system failure 14; septic tank efﬂuent 30 Seville, Spain 61 sewage lagoon 29 Shanghai: drinking water 149; Exposition 153 shellﬁsh 192, 238 Shengyang, China 85, 96 shrimp production 251 Silkerode, Germany 70 S-metolachlor (BicepII Magnum) 235 softstem bulrush 45 soil: inﬁltration rages 276; particle size 276; texture classiﬁcation 276 Songhua River 217, 221 Spalene Poroco, Czech Republic 65
spider lily 132 spikesedge 110 Sprilliums 83 standard speciﬁcations 84 Stapleton, Colorado 178 Stoneville, Mississippi 249 stormwater: algae 191; basin see stormwater basin; calculation methods 181; case study 217; channelization 179; contaminants and land use 186; design storms 180; development impacts 177; E. coli 190; ﬂood control 179; heavy metals 189; hydrologic soil groups 185; isopluvial map 181; JEL Wade Park see stormwater, JEL Wade Park; municipal planning 178; nitrogen 190; off-line treatment wetlands 197; parcel 177; parking lot contaminants 187; phosphorus 190; planning 177; rainfall types 180; rational method 181; roadway contaminants 188; runoff curve numbers 185; run-off rate 176; sedimentation basin 199; stream impact 189; subsurface gravel wetland see stormwater, subsurface gravel wetland; toxicity 188; TR-55 182–186; treatment 176; treatment landscapes 192; typical contaminants 186; urban contaminants 189; volume 176; wetland 47, 97 stormwater basin: management 175; regulations 179; run-off characteristics 176; scouring 103 stormwater, JEL Wade Park 192; design 193; performance 196; plan 194; plants 194; secondary beneﬁts 197; water management 195; water treatment 195; weirs 194 stormwater, subsurface gravel wetland: ﬁlter media 201; ﬂow sequence 199; materials 199; outlet structure 201; performance 204; piping 201; retroﬁt 204; sedimentation basin 199; water management 203; water quality 203 stream assessment 17, 19 Street Edge Alternative 214 Strelitzia reginae 130 Streptococci 92 subsurface ﬂow constructed wetland 21 sulphate 264 sulphur dioxide 264 suspended solids 25 sustainable development 19
sustainable water use, barriers 15 swine 247 synthetic liners 36 Tabor School, Portland Oregon 205 Taiwan 38 Talking Water Gardens 41–43, 44; birds 46; performance 45; plants 45 Tanghe River 149, 173 tanneries 260; wetland performance 261 Taro 132 tartaric acid 259 temporary pool 206 tertiary treatment 26 Thalia spp. 127 thermoelectric power generation, water use 264 thermoelectric power generators 9 Tianjin, China 99, 216 tidal-ﬂow 71, 74 Tilapia 251 Titusville, Florida 21 TKN 27 TMDL 23, 41 toluene 255 Tonalide 92 total Kjeldahl nitrogen (TKN) 27 Total Maximum Daily Load 23, 41 total suspended solids 27; standard 23 Town Brook, New York 242 TR-55 215 Triclosan 92 tropical sundew 38 trout 26, 249, 252 TSS 245, 248 Turenscape I, 229 Typha latifolia 38, 45, 104–106 Typha orientalis 38 umbrella papyrus 38 University of New Hampshire: bio-retention basin 212; Stormwater Center 199, 211 Up-ﬂow: wetland 74; anaerobic sludge blanket (USAB) 76 US Clean Water Act 244 US Natural Resources Conservation Service 209 USAB see up-ﬂow: anaerobic sludge blanket Vermont, USA 244 vertical subsurface ﬂow 22, 70, 242, 247, 250; wetlands: ammonia 82; bacteria 82;
case study 70, 81, 85; clogging 79; conﬁguration 71; Danish guidelines 79; denitriﬁcation 83; depth 78; ﬁlter media 78; French system 73–74, 77, 79, 82; hydraulic loading 77; intermittent loading 70; liner 78; loading 76; nitriﬁcation 83; nitrogen 82; pathogenic bacteria 84; phosphorus 84; plants 79; pretreatment 75; shape 77; Shenyang 85; sizing 76; sub-basin 75, 81; tidal-ﬂow 74; two-stage 81; up-ﬂow 74, 259, 266; wetlands 266 Vietnam, wetland 250 Villanova University, Pennsylvania 209, 211 volatile organic compounds 263 wapato 46 Warmwater Aquaculture Research 249 wastewater: characteristics 25; pretreatment 30, 33; strength 25; treatment plants 17; treatment standards see wastewater, treatment standards wastewater, treatment standards 26; nitrogen 26; organic matter 26 water: allocation 15; quantity 9; resource planning 9; temperature 41, 43, 45; water use water cost: agriculture 16; Europe 15; United Kingdom 15; USA 15 water hyacinth 38, 133 water hyssop 132 water lettuce 134 water primrose 38
water use: aquaculture 10; domestic 15; livestock 10; mining 10; water use per kilowatt-hour 10 Watsonia borbonica 104 wetland: assessment 17, 19; birds 45; images 45; insulation 67, 255; loss 17; visitors 44 wetland plants 98; common species 99; ﬂoating 133; mixed community 100; native species 104; water depth 99, 101–102 Willamette River 41 Wilmington, North Carolina 192 winery: wastewater 258; wetland 259 Wisconsin Department of Natural Resources 214 worms 83 Wuhan, China 1 Wulijie, China 2; controlling plan 4, 7; ﬂooding 3; habitat 3; intermediate corridor 6; stormwater ﬂow plan 3; urban corridor 4, 6; widest corridor 5 xylene 123, 255 Yangtze River 14, 20, 144, 263 yellow ﬂag 79 yellow water lily 38 Zantedeschia aethiopica 128 Zasada, Czech Republic 67 zeolite 60 zinc 66 Zitenice, Czech Republic 64