Sediment And Phosphorus Dynamics Behind Weirs In Agricultural Drainage Ditches

Author : Matthew T. Moore and Robert Kroger
Publisher :
ISBN 13 : 9788130803760
Total Pages : 259 pages
Book Rating : 4.8/5 (37 download)

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Download or read book Agricultural Drainage Ditches: Mitigation Wetlands for the 21st Century written by Matthew T. Moore and Robert Kroger and published by . This book was released on 2010-05-01 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: About the Book : - As populations across the globe burgeon and pressures on agricultural production intensify, natural resources of adjacent and downstream aquatic ecosystems are often degraded. Classically, non-point source contamination of nutrients, sediments and pesticides result in aquatic ecosystem degradation, downstream river eutrophication, and in some cases, eventual coastal ecosystem imbalance with hypoxic zones occurring in coastal waters. Managers, action agencies and conservationists want to reduce impacts of non-point source contamination on receiving systems. Best management practices such as no-till, implementation of buffer strips, riparian corridors, and conservation fertilizer applications are all management applications that reduce the concentration and load of contaminants to aquatic systems. Drainage is a common management practice on most agricultural production, as farmers require water to move away from maturing crops avoiding crop senescence and loss of yield by flooding and soil saturation. Thus, agricultural drainage ditches are ubiquitous features of the production landscape. Traditionally agricultural drainage ditches were viewed simply as drainage tools, a conduit to rapidly move water away from the production landscape and into adjacent aquatic systems. However, there is a paradigm shift occurring whereby scientists and managers are viewing these drainage ditches as integral tools in the management of non-point source contamination. Along with these studies, multiple other studies are beginning to show the ecological importance of drainage ditches and their contribution to both the agricultural and broader ecological landscape. This book highlights cutting-edge research being carried out on agricultural drainage ditches. Chapter 1 (Werner et al.) is aimed at characterizing the benthic macroinvertebrate communities in secondary and tertiary agricultural drainage ditches in Yolo County, California. These ditches were approximately 1-2 m wide, about 0.1-0.6m in depth, and were ephemeral in nature. Despite the ephemeral nature of these secondary and tertiary ditches, 14 different benthic macroinvertebrate taxa were found, of which baetid mayflies were the only EPT (ephemeroptera, plecoptera, and trichoptera) taxa found. Interestingly, species richness was significantly correlated with water depth, and oligochaetes were most abundant where substrate quality was poor (percentage organic, mud, sand, gravel, cobble and hardpan clay) and dissolved oxygen was low. By examining the differences between perennial and ephemeral ditches, it was shown that perennial sites had larger, more diverse invertebrate communities; however, it was not discredited that these differences could have been the result of proximity to colonization and adversely affected by potential sources of nonpoint source contamination. This study highlighted the need for more in depth work into quantifying the role macroinvertebrates play in drainage ditch dynamics and how alterations to ditch management might change the population structure and diversity. Chapter 2 (Feldman et al.) complements the benthic macroinvertebrate research of Chapter 1, highlighting macroinvertebrate assemblages of agricultural drainage ditches of northeast Arkansas, in the floodplain of the Mississippi River. Feldman et al. noted that the characteristic benthic macroinvertebrate fauna will be reflective of the hydraulic residence time of the respective ditch surveyed. In this study, Feldman et al. assessed ten drainages (ranging in size from primary intercept ditches to riverine, quaternary ditches) and characterized over 68 different macroinvertebrate taxa. Mean annual taxa metric scores ranged from 16 in primary systems to 24 in riverine/quaternary ditches. Interestingly seasonal sampling collections highlighted seasonal differences in the macroinvertebrate population assemblage. By combining measures of macroinvertebrate diversity and physical environmental quality parameters and evaluating how they change temporally, benthic macroinvertebrate can be utilized as indicators for changes in water quality within water bodies. Often in primary drainage ditches low EPT richness was not a function of degraded water quality, but rather a lack of habitat diversity that prevented diverse EPT establishment. The third chapter (Smiley et al.) addressed understanding the knowledge of population and community ecology of fishes within agricultural drainage ditches. Often agricultural drainage ditch systems are straightened channels lacking riparian vegetation in an agricultural landscape. Furthermore, these agricultural drainage ditches undergo periods of intensive management that includes dredging and herbicide application to decrease channel hydrologic capacity and prevent vegetation (both woody and herbaceous) establishment. This literature survey identified documents and publications that documented fish responses to physical habitat modifications and/or exposures to agricultural contaminants. The study identified over 800 possible publications with selection criteria including: agricultural land use in watershed, headwater streams, and streams that were channelized. From the literature review, Smiley et al. found that fishes appeared to be integral components of agricultural drainage ditches and were often correlated with instream habitat variables of channelization and the effects of nonpoint contaminants of herbicides and nutrients. Future research is looking at integrating the drainage ditches ability to mitigate nonpoint source loads as well as provide habitat for fish communities. In Chapter 4, Pierce and Pezeshki examined another biological component of agricultural drainage ditches, namely vegetation. This research begins to disseminate the limitations of vegetation in establishment, productivity and function in agricultural drainage ditches. Primary systems such as ditches are dynamic environments in terms of hydrological fluctuations, soil water stress conditions, and the influence of anthropogenic disturbances associated with land use patterns (i.e. fertilizer, herbicide loads and concentrations). Thus, to survive ditch conditions, plants (whether annual or perennial) must possess life history characteristics that allow them to become established and withstand periods of intense hydrological fluctuations and high loads / concentrations of chemicals. This chapter offers some insights to the current knowledge on how plants mitigate agricultural pollutants and provides an outline for the abiotic factors that will limit the establishment and productivity of ditch vegetation. The synthesis outlines the effects of ditch management techniques such as 2-stage ditches, the use of low-grade drainage control structures and how these influence the biogeochemical environment in drainage ditches. Furthermore the authors provide examples of studies that have shown the ability of vegetation exposed to various environmental scenarios commensurate with drainage ditches (e.g. Leersia oryzoides, Juncus effusus and Bacopa monnieri). The fifth chapter (Kleinman et al.) investigated the role agricultural drainage ditches play in nutrient transfers from manured fields in the Delmarva Peninsula, on the Atlantic Coastal Plain. This research in the Chesapeake Bay watershed is driven primarily by the poor water quality in the Bay (hypoxic zones and eutrophic conditions resulting in algal blooms), which occurs as a result of nutrient and sediment loadings from agriculture upstream. According to the public drainage associations, drainage ditches are designed as conduits to remove excess water from the production landscape, with the removal of vegetation a common management practices to improve drainage. Research findings have shown that ditches, no matter the size, can contribute significantly to nutrient export. Small drainage ditches with high concentrations and large water volumes can contribute significantly to downstream aquatic contaminant loads. Furthermore, even ditches that do not have a point source of nutrient loading directly, given high background concentrations, will yield significant contributions to the nutrient loadings in years of high flow. This research provides insight into how management of drainage ditches needs to be incorporated in broader watershed nutrient management programs. In Chapter 6, Saunders and Brown examined how drainage ditches, in particular sediments, play a role in phosphorus sorption from municipal wastewater in Peru, South America. Phosphorus is a contaminant across the globe, associated with agriculture but also closely associated with urban and rural communities (e.g. detergents). Phosphorus in aquatic systems results in algal blooms, eutrophication and a potential concern for tourism due to the aesthetics associated with water quality and indirect effects on fisheries. This study based in the Oxapampa community in Peru examined three municipal drainage ditches and evaluated the role sediments played in phosphorus sorption. Total phosphorus of sediments was very high (2171 19, 277 mg P /kg) with the majority of P associated with Fe / Al oxyhydroxides. Sorption capacities and physicochemical characteristics varied between seasons (i.e. clay and organic matter contents). The chapter highlights how drainage ditches can be both sinks and sources of soluble reactive phosphorus, and that sorption capacity is influenced by the timing of phosphorus exports (i.e. seasonality) and the magnitude of export. Next, Penn et al. (Chapter 7) evaluated various treatment structures in agricultural drainage ditch management for water quality improvement. Drainage ditches are conduits for contaminant transfer from the agricultural production landscape to downstream aquatic ecosystems. Therefore, improving the ecological benefit of drainage ditches to water quality improvement can occur by implementing management strategies of controlled drainage. Penn et al propose implementing a flow control structure which controls water depth within the drainage ditch. In addition, filter structures, filled with various sorbents can be used to enhance nutrient or contaminant mitigation. The study addresses the importance of various sorbent materials and discusses in detail the advantages and disadvantages of each. Furthermore, the authors address design considerations of the filter structures, ditch filter designs (pond and dam structures), and what these structures mean in a broader system management within the watershed. The eighth chapter (Stringfellow et al.) examined the water quality changes occurring in agricultural drains associated with varying degree of riparian buffers in the San Joaquin Valley of California. The study evaluated nitrate-nitrogen, soluble reactive phosphate and total suspended solids concentrations and loads that were associated with five different study sites, all of which had varying degrees of riparian function. Riparian function was evaluated with the California Rapid Assessment for Wetlands, a scientifically defensible tool to evaluate the overall health of wetland ecosystems. The stated hypothesis was that drainage ditches with high degrees of riparian function would have a beneficial effect on water quality in drainages in comparison to drainages with less vegetation and less riparian habitat. Results showed that areas with improved riparian habitat and higher degrees of riparian function will buffer drainages from external anthropogenic sources of contamination, but the in-stream water quality improvement of drainage ditches is not enhanced by simple improvements to ditch bank vegetation. It was recommended modifications to the in-stream drainage management will likely improve in-stream removal of nutrients and sediments. Chapter 9 (Jayakaran et al.) discussed construction, maintenance, and geomorphic evolution of low-gradient agricultural drainage ditches. Important issues such as bank erosion, contaminant transport, and general ditch design were not initially part of early settlers plans when digging ditches to drain water-holding landscapes for agriculture. Fluvial features consistent with natural streams play a significant role in the management and design of these ditches. Significant work on drainage ditches in the Midwest feeding tile or sub-surface drainage systems has been achieved. This chapter is an excellent resource for those interested in specific design criteria for modifying channels. The tenth chapter (Farris et al.) discussed the toxicity of atrazine and lambda-cyhalothrin amendments in agricultural drainage ditches, and evaluated the ability of the drainage ditches to potentially mitigate downstream effects of these pesticides. Atrazine and lambda-cyhalothrin are two agro-chemicals commonly utilized in the agricultural production landscape and are often carried with surface runoff and spray-drift into adjacent aquatic ecosystems. The study evaluated a drainage ditch system located in the Mississippi Delta Management Systems Evaluation Area (MDMSEA) and its ability to reduce the toxicity of the above mentioned pesticides. The 28 d trial time span failed to identify the exact duration at which acute toxicity exposures to sediment exposed to these two agro-chemicals would have no sublethal effects. Toxicity of aquatic invertebrates occurred within the drainage ditch ecosystem, however, the structure and function of agricultural drainage ditches for mitigation is an important ecological component that warrants significant further investigation. The study alludes to further research within agricultural drainage ditches from an ecotoxicological context. The eleventh and final chapter (Bennett et al.) improves the understanding on pesticide mitigation in drainage ditches highlighted in Chapter 10, by looking more specifically at the effectiveness of vegetated agricultural drainage ditches in mitigating aquatic insecticide loadings. Often adjacent aquatic ecosystems (i.e. surface drainage ditches) to agricultural production are influenced by insecticide loadings resulting from runoff and spray-drift. This chapter focuses on the use of agricultural drainage ditches as best management practices in reducing insecticide loadings in two very different scenarios: agricultural ditches in Mississippi under simulated runoff conditions and in ditches in the Western Cape of South Africa, under natural runoff and spray-drift conditions. The results from the study showed that in both ditch systems, concentrations of bifenthrin and lambda-cyhalothrin were reduced rapidly with distance and time. For the Mississippi ditches, it was calculated that ditch lengths of 120 m and 280 m were required to reduce bifenthrin and lambda-cyhalothrin to 1% and 0.1%, respectively, of the original loadings. In the Western Cape scenario similar relationships occurred where pesticide concentrations (azinphos-methyl) declined with distance. It was noted that the aquatic macrophyte component of the drainage ditches played an important role in the retention and providing available surface area for pesticide attachment in agricultural ditch systems. Authors validated the effectiveness of mitigation with a series of aquatic toxicity bioassays and benthic surveys. As one can see from the variety of research topics addressed in the chapters of this book, agricultural drainage ditch research is rapidly shifting the use of the agricultural drainage ditches away from traditional system conduits to important management tools in the agricultural landscape. As alluded to at the end of most chapters, these research topics have provided vital answers to the importance of drainage ditches, but they have also developed a suite of questions that demand further research. The advancement of drainage ditch science is of benefit to scientific community, management and relevant stakeholders. In proving their worth for ecological services of contaminant mitigation and biodiversity maintenance, drainage ditches can be influential tools in developing broad sweeping management objectives for watershed scale water and contaminant management.