|Smith Jr, Sammie|
Submitted to: American Chemical Society Symposium Series
Publication Type: Proceedings
Publication Acceptance Date: 1/13/2003
Publication Date: 4/2/2004
Citation: Smith Jr, S., Cooper, C.M. 2004. Pesticides in shallow ground water and lake water in the Mississippi Delta Management Systems Evaluation Area. In: Nett, M.T., Locke, M.A., and Pennington, D.A., editors. Water Quality Assessments in the Mississippi Delta: Regional Solutions, National Scope. ACS Symposium Series 877. Washington, D.C.: American Chemical Society. p. 91-103. Interpretive Summary: Development of region-specific alternative farming systems composed of combinations of selected best management practices (BMPs) is crucial to protecting the surface and ground water resources and improving ecological and environmental quality of the entire Mississippi Delta. Many of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project (BMPs) that have been implemented are designed to slow surface runoff and reduce agrichemical (nutrients and pesticides) and sediment movement into adjacent water bodies, namely, oxbow lakes. These BMPs also tend to increase infiltration and the potential for dissolved agrichemicals to leach downward into the soil profile and degrade shallow ground water quality. The paper reports the results of research on the determination and characterization of pesticide movement in shallow ground water during three water years (1996-1998) of the first 5-years of the MDMSEA project. Findings on the presence of pesticides in monthly water samples collected from the three MDMSEA oxbow lakes during the years 1998-2000 are also presented. Results demonstrate that the project-imposed BMPs caused no shallow ground water quality problems in any of the three MDMSEA watersheds. Pesticides that leached into the soil profile were likely degraded in the biologically active upper soil layers. Evaluation of shallow ground water quality in the MDMSEA watersheds continues, but at a greatly reduced level. Pesticide concentrations found in lake water samples were generally below levels considered harmful to aquatic animal species and only occurred seasonally. The MDMSEA project has resulted in significant improvement in oxbow lake water quality.
Technical Abstract: BMPs in watersheds of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project (BMPs) were designed to slow surface runoff and reduce agrichemical/sediment transport to adjacent oxbow lakes. Because they also tend to increase the potential for agrichemicals to leach into the soil profile, research was conducted to determine/characterize pesticide movement in shallow ground water during three water years (1996-1998) of the first 5-years of the project. A total of 622 well samples were collected and there were only 5 detections, all in the Beasley Lake watershed. All detections were at extremely low levels, transient in nature, and present no pesticide- related water quality problems. Pesticide concentrations in monthly water samples collected from the 3 MDMSEA lakes during the years 1998- 2000 were also determined. Samples totaled 104, with 88 pesticide detections above the 0.10 ppb level. Of these, 76 detections were herbicides and 12 were pyrethroid insecticides. Herbicide concentrations in lake water were well below LC50 (96 hour) values for fish which are in the range of 2.4-18 mg/L (ppm). The highest herbicide concentration found in the lake water samples was about 13 ppb. The pyrethroids LC50 (96 hour) values for fish are in the range of 0.0002- 0.0082 mg/L (0.2-8.2 ppb). Pyrethroid concentrations in lake water were in the range of about 0.2-1.6 ppb and with the exception of zeta- cypermethrin were transient in nature.