The Role of Vegetated Drainage Ditch Research in the Mississippi Delta

Chapter 14

The Role of Vegetated Drainage Ditch Research in the Mississippi Delta: Current Results and Future Directions 1

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Matthew T. Moore , Charles M. Cooper , Erin R. Bennett, Sammie Smith, Jr. , F. Douglas Shields, Jr. , and Jerry L. Farris Downloaded by MONASH UNIV on December 6, 2014 | http://pubs.acs.org Publication Date: April 13, 2004 | doi: 10.1021/bk-2004-0877.ch014

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National Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 598 McElroy Drive, Oxford, MS 38655-1157 Environmental Sciences Program, Arkansas State University, P.O. Box 847, State University, AR 72467 2

Since 1998, two vegetated agricultural drainage ditches within the Mississippi Delta Management Systems Evaluation Area (MDMSEA) have been used to determine whether ditches can effectively mitigate concentrations of pesticides associated with runoff. Through simulated storm events, pesticides and water were amended into drainage ditches at concentrations indicative of a typical runoff event. Study results allude to the value of ditch vegetation in transferring pesticides out of the aqueous phase, thereby mitigating potential risks to aquatic receiving systems. Between 95 and 97% of the total mass of pyrethroid insecticides amended was successfully transferred from the aqueous to plant material within three hours following the simulated runoff events. Pesticide toxicity evaluations provided data indicating remediation of contaminated ditch water and sediment following simulated storm events. Analysis of fate data indicated that ditches can effectively mitigate pesticide transport and risk of aquatic exposure within reasonable ditch lengths (50 to 400-m), depending upon contributing drainage area and assumed rainfall and runoff percentages.

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© 2004 American Chemical Society

In Water Quality Assessments in the Mississippi Delta; Nett, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

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Downloaded by MONASH UNIV on December 6, 2014 | http://pubs.acs.org Publication Date: April 13, 2004 | doi: 10.1021/bk-2004-0877.ch014

Introduction Encroachment of human activities upon natural ecosystems has increasingly caused problems over the last century. In recent years the urbanization of formerly rural areas has transformed hill, forest, and farm land into housing subdivisions, retail outlets, and parking lots. These trends are not without an environmental cost. Land use changes may result in increased erosion and nonpoint source pollution. Historically agriculture has been targeted as a major contributor of non-point source pollution, and for draining wetlands and clearing timber in order to establish production acreage to meet growing demands of America's food and fiber requirements. There is little argument that agriculture is responsible for a proportion of the nation's water quality problems (/). Issues of suspended sediments, erosion, contaminant loads of bacteria (animal operations), nutrients, and pesticides are of concern to the agricultural community. In the cases of soil erosion and nutrient or pesticide runoff, both the farmer and users of the receiving water body are negatively affected. While the farmer is losing valuable soil and applied nutrients or pesticides, the receiving water body is negatively impacted by pollution. Since agriculture is a major contributor of non-point source pollution, government agencies [primarily the United States Department of Agriculture's Agricultural Research Service (USDA-ARS) and Natural Resource Conservation Service (USDA-NRCS)] and universities have intensified their commitment to decreasing effects of non-point source pollution through developing and improving best management practices (BMPs). Several "edge-of-field" and agronomic BMPs exist with current guidelines for implementation widely available (2-P). Now, a new, innovative BMP is being suggested for implementation—vegetated agricultural drainage ditches. Most agricultural production acreage is surrounded by a network of drainage ditches, which often leads to a receiving stream, river, lake, or reservoir. Historically these ditches have been managed according to their capacity to transport water discharged from fields following controlled releases (e.g. rice rields) or storm runoff events (10). In actuality, these ditches have additionally served as sites for contaminant transfer and transformation. The objective of this research is to evaluate the effectiveness of vegetated drainage ditches in mitigating concentrations of agricultural contaminants. If pollutants can be transferred from the water column to plant material via sorption, potential effects upon flora and fauna in aquatic receiving systems can be mitigated. On a broader scale, it is anticipated that this research will help develop a greater understanding of overall drainage ditch function and ecology and how those relate to issues of total maximum daily loads (TMDLs).


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Materials and Methods


The Mississippi Delta Management Systems Evaluation Area (MDMSEA) is comprised of three experimental watersheds: Beasley Lake and Thighman Lake (both located in Sunflower County, Mississippi) and Deep Hollow Lake (located in Leflore County). Drainage ditch simulated runoff experiments were conducted within the Mississippi Delta Management Systems Evaluation Area (MDMSEA) in 1998 and 1999. One drainage ditch was chosen each year, with the first located in the Beasley Lake watershed (1998), while the second study was located in a drainage ditch within the Thighman Lake watershed. Both studies specifically examined the capability of a vegetated drainage ditch to reduce pesticide transport and the risk of aquatic exposure..

Beasley Lake Study For evaluation in 1998, a 60-m portion of a drainage ditch leading into the riparian zone adjacent to Beasley Lake was chosen for evaluation. Sampling stations were located at 10 m up-ditch of the simulated runoff injection point, as well as 10-m, 20-m, 40-m, and 50-m down-ditch of the injection point. Pesticides examined in this study included the triazine herbicide atrazine (2-chloro-4ethylamino-6-isopropylamino-s-triazine) and the pyrethroid insecticide lambda cyhalothrin [alpha-cyano-3-phenoxybenzyl-H2-chloro-33,3-trifluorol-enyl)-2idimethyl cyclopropanecarboxylate]. Assumptions for the simulated runoff event included a 2 ha contributing area subjected to a 0.64-cm rainfall (with 10% of the rainfall actually "running off), and 5% of the applied pesticides (based on recommended application rates on 2 ha) being transported with the runoff. A total volume of 6400-L of water amended as simulated rainfall/runoff. No sediment was added to the simulated runoff mixture ensuring that the applied chemicals were biologically available. This is a conservative assumption relative to die real world. Pesticides and water were mixed in a 110-L polyethylene mixing chamber before being gravity fed into a 2-m length of 7.6-cm PVC pipe where delivery into the ditch occurred. In addition to pre-study sample collections, water was collected at time intervals 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 24 h, 7 d, 14 d, and 28 d post-exposure. Sediment and plants were collected prior to initiation of experiment, as well as 1 h, 3 h, 24 h, 7 d, 14 d, and 28 d post-exposure. Sediment collected for analysis came from approximately the top 4 to 6-cm of the ditch bed. Only those plant materials exposed in the water column (from top of sediment to top of the water column) were collected for analysis. All collected samples were analyzed for the presence of atrazine and lambda cyhalothrin using gas


197 chromatography-electron capture detection (Tracor 540 gas ehromatograph equipped with a Dynatech Precision GCAl IV autosampler and a 15 m χ 0.53 mm i.d. J&W DB-1 Megabore® column (/ /, 12).


Thighman Lake Study A similar study was conducted in 1999 evaluating a 650-m portion of a drainage ditch in the Thighman Lake watershed. Sampling stations were located 10 m upditch of the simulation injection point, as well as 10-m, 20-m, 40-m, 60-m, 80-m, 100-m, 200-m, 400-m, and 650-m down-ditch. Lambda cyhalothrin and bifenthrin [[2 methyl (l,r-biphenyl)-3-yl] methyl 3

The Role of Vegetated Drainage Ditch Research in the Mississippi Delta

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