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Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored Wetlands

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Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored Wetlands UC Davis UC Davis Previously Published Works Title Chapter One Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored Wetlands Permalink https://escholarship.org/uc/item/72b0c5ct Authors O'Geen, AT Budd, R Gan, J et al. Publication Date 2010 DOI 10.1016/s0065-2113(10)08001-6 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Provided for non-commercial research and educational use only. Not for reproduction, distribution or commercial use. This chapter was originally published in the book Advances in Agronomy, Vol. 108, published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who know you, and providing a copy to your institution’s administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution’s website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial From: A. T. O’Geen, R. Budd, J. Gan, J. J. Maynard, S. J. Parikh, and R. A. Dahlgren, Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored Wetlands. In Donald Sparks, editor: Advances in Agronomy, Vol. 108, Burlington: Academic Press, 2010, pp. 1-76. ISBN: 978-0-12-381031-1 © Copyright 2010 Elsevier Inc. Academic Press. Author's personal copy CHAPTER ONE Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored Wetlands A. T. O’Geen,* R. Budd,† J. Gan,‡ J. J. Maynard,* S. J. Parikh,* and R. A. Dahlgren* Contents 1. Mitigating Pollution with Wetlands 3 1.1. Types of anthropogenic wetlands 4 1.2. Governing factors influencing CWs 6 1.3. Contaminant removal processes 7 1.4. Vegetation 9 2. Suspended Sediment 10 3. Pesticides 12 3.1. Herbicides 12 3.2. Organophosphate insecticides 15 3.3. Pyrethroid insecticides 16 3.4. Pesticide removal 20 4. Nitrogen (N) 24 4.1. Environmental impacts 24 4.2. N cycling in CWs 25 4.3. N removal efficiency 28 5. Phosphorus (P) 32 5.1. Environmental impacts 32 5.2. Phosphorus forms in CWs 33 5.3. P transformations 34 5.4. Removal efficiencies of P fractions 37 5.5. Wetland management strategies to improve P removal 38 6. Dissolved Organic Matter 38 6.1. DOM sources 39 6.2. DOM sinks 40 6.3. DOM input–output budgets from agricultural wetlands 41 * Department of Land, Air and Water Resources, University of California, Davis, California, USA { California Department of Pesticide Regulation, Sacramento, California, USA { Department of Environmental Sciences, University of California, Riverside, California, USA Advances in Agronomy, Volume 108 # 2010 Elsevier Inc. ISSN 0065-2113, DOI: 10.1016/S0065-2113(10)08001-6 All rights reserved. 1 Author's personal copy 2 A. T. O’Geen et al. 7. Trace Metals 43 7.1. Sources of trace metals to agricultural soils 44 7.2. Trace metal fate and transport in agricultural soils 45 7.3. Trace metals in saturated soils and wetlands 45 8. Pathogens 48 8.1. Pathogen removal 48 8.2. Case study: Agricultural wetlands treatment of irrigation tailwaters 50 9. Other Water-Quality Constituents 51 9.1. Salinity 51 9.2. Biological oxygen demand 52 10. Design and Management 52 10.1. Hydrology 53 10.2. Dimensions and design 55 10.3. Placement 57 10.4. Managing vegetation 58 10.5. Design features for mosquito control 59 11. Summary 59 References 60 Abstract Nonpoint source pollution (NPSP) from agricultural runoff threatens drinking water quality, aquatic habitats, and a variety of other beneficial uses of water resources. Agricultural runoff often contains a suite of water-quality contami- nants, such as nutrients, pesticides, pathogens, sediment, salts, trace metals, and substances, contributing to biological oxygen demand. Increasingly, growers who discharge agricultural runoff must comply with water-quality regulations and implement management practices to reduce NPSP. Constructed and restored wetlands are one of many best management practices that growers can employ to address this problem. This review focuses on the ability of constructed and restored wetlands to mitigate a variety of water-quality contaminants common to most agricultural landscapes. We found that con- structed and restored wetlands remove or retain many water-quality contami- nants in agricultural runoff if carefully designed and managed. Contaminant removal efficiency generally exceeded 50% for sediment, nitrate, microbial pathogens, particulate phosphorus, hydrophobic pesticides, and selected trace elements when wetlands were placed in the correct settings. There are some potentially adverse effects of constructed and restored wetlands that must be considered, including accumulation of mercury and selenium, increased salinity, mosquito habitat, and greenhouse gas emissions. Proper wetland management and design features are discussed in order to reduce these adverse effects, while optimizing contaminant removal. Author's personal copy Mitigating Nonpoint Source Pollution 3 1. Mitigating Pollution with Wetlands An emerging challenge for agriculture is to feed the world without adversely affecting the environment. Global demand for food is growing at an alarming rate. According to FAO predictions, food production must increase 40% by 2030 and 70% by 2050 to sustain the planet’s population growth (OECD-FAO, 2009). Today, roughly 1.4 billion hectares of cropland are in production across the planet, yet to sustain this emerging global demand, cropland area would have to more than double (OECD-FAO, 2009). At the same time, prime farmland is being lost to urbanization and other land uses. The loss of this productive farmland has displaced farming into marginal lands that are more erosive and require more inputs than those required for prime farmland (Charbonneau and Kondolf, 1993). Thus, soil and water resources will be subjected to added pressures in the future requiring cost effective, best management practices (BMPs) to ensure environmental protection. Nonpoint source pollution (NPSP) is a global problem affecting the safety of our drinking water supply and aquatic habitats. According to the 2000 National Water Quality Inventory, agriculturally derived NPSP is the leading cause of water-quality degradation in surface waters (US EPA, 2002). Pollutants originating from agricultural runoff include sediment, nutri- ents (N and P), pesticides, pathogens, salts, trace elements, dissolved organic carbon (DOC), and substances that contribute to biological oxygen demand (BOD). For example, discharge of nutrients into aquatic ecosystems has lead to dramatic shifts in trophic relationships (Boesch et al., 2001) including hypoxia/ anoxia induced ‘‘dead zones’’ in more than 400 locations worldwide (Diaz and Rosenberg, 2008). Thus, new and effective management practices for agri- culture must be identified, tested, and monitored in order to reduce the impacts of agriculture on the sustainability of water resources. Wetlands are widely advertised as critical components of our planet providing a wide variety of ecosystem services: kidneys of the hydrologic cycle by removing pollutants, biodiversity hot spots, habitats of rare and endangered species, ground water recharge zones, localized areas for flood protection, carbon sinks, and aesthetic value (Zedler, 2003). Upon settle- ment of the United States, the lack of understanding for the role of wetlands and drive for agricultural production resulted in a loss of over 53% of the nation’s wetlands (Dahl, 1990). California and Texas, two states leading agricultural production in the United States, have lost more than a com- bined 5 million hectares of wetlands. Much of this loss was as result of programs in the United States such as Swamp Buster, which encouraged the conversion of marginal land (e.g., wetlands) into agricultural production. Coincident with this landscape conversion was the rise in use of agricultural chemicals. As a result, the filtration effect of wetlands has been uncoupled from riparian environments resulting in severe degradation of the nation’s Author's personal copy 4 A. T. O’Geen et al. (and the planet’s) water resources. Only in the last few decades have wet- lands been recognized for their potential role to ameliorate NPSP. Traditionally, constructed and restored wetlands have been developed in agricultural settings to improve wildlife habitat, mainly through the U.S. Conservation Reserve Program and the Wetlands Reserve Program (WRP). The WRP is an outreach effort administered through the Natural Resource Conservation Service (NRCS) and its partners. It is designed to provide financial and technical assistance to landowners to restore, enhance, and protect wetlands and surrounding surface waters. As of 1999, there were a total of 785,000 ha of marginal farmland that have been enrolled in the WRP (Mitsch and Gosselink, 2000). The conversion of floodplain agro- ecosystems to wetlands is becoming a popular land-use practice nationwide (Fig. 1), yet little information exists to document how these wetlands filter water-quality contaminants in runoff from agricultural fields. 1.1. Types of anthropogenic wetlands There are many different definitions of wetlands from a variety of
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