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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Water Quality and Ecology Research » Research » Publications at this Location » Publication #146295
Title: GROUNDWATER NUTRIENTS IN THE BEASLEY LAKE WATERSHED OF THE MISSISSIPPI DELTA MANAGEMENT SYSTEMS EVALUATION AREA

Author
item Dabney, Seth
item SCHREIBER, JONATHON - RETIRED ARS
item Smith Jr, Sammie
item Knight, Scott

Submitted to: American Chemistry Society Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/10/2003
Publication Date: 3/1/2004
Citation: Dabney, S.M., Schreiber, J.D., Smith Jr, S., Knight, S.S. 2004. Groundwater nutrients in the Beasley Lake watershed of 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. 75-90.

Interpretive Summary: Interest is high to know the impact of agriculture on water quality. In some parts of the country, agriculture has been blamed for elevated levels of nutrients in groundwater leading to eutrophication and drinking water contamination. We conducted this research to determine what impact the intensive agricultual activity in the Mississippi Delta had on nutrients in shallow groundwater. We monitored shallow groundwater nutrient concentrations in an intensively-farmed area surrounding Beasley Lake in the Mississippi Delta. Over the period 1996-2001, groundwater was periodically sampled from 5 to 15 foot deep observation wells in the grassed borders of agricultural fields and from 2 to 10 foot wells in an extensive riparian forest between the cropland and an oxbow lake. Shallow groundwater samples were analyzed for dissolved organic C (DOC), Cl, NO3-N, NH4-N, and PO4-P. Nitrate-N concentrations in shallow groundwater were very low, usually <1.0 mg/L, in both the agricultural and riparian areas, and pose no threat to well water. When compared to groundwater quality in Midwestern MSEA projects or upland agricultural watersheds in northern Mississippi, shallow groundwater in the Delta is relatively high in DOC and PO4-P and much lower in NO3-N. Considering warm soil temperatures, abundant rainfall, and a year-round carbon supply, high rates of soil denitrification are suspected for the low dissolved NO3-N concentrations. Since farmers harvest more P in crops than they apply in fertilizer, relatively high groundwater PO4-P values observed reflect the high native P content of Delta soils. Our results suggest that natural factors in the Delta overcome the risk of nitrate groundwater contamination associated with intensive agricultural production practices and support the concept that appropriate P reference levels for Mississippi Delta waters may be higher than in other ecoregions of the nation.

Technical Abstract: Shallow groundwater was monitored in an intensively-farmed area of the Mississippi Delta. Samples were obtained during 1996-2001 from 1.5, 3.0, and 4.5 m deep observation wells in the grassed borders of agricultural fields and from 0.6, 1.5, and 3.0 m wells in an extensive riparian forest between the cropland and an oxbow lake. Samples were analyzed for dissolved organic C (DOC), Cl, NO3-N, NH4-N, and PO4-P. Nitrate-N concentrations in shallow groundwater were very low, usually <1.0 mg/L, in both the agricultural and riparian areas, and pose no threat to well or surface water quality. When compared to Midwestern MSEA (Management System Evaluation Area) projects or upland agricultural watersheds in northern Mississippi, shallow groundwater in the Delta is relatively high in DOC and PO4-P and much lower in NO3-N. Considering warm soil temperatures, abundant rainfall, and a year-round labile carbon supply, high rates of soil denitrification are suspected for the low dissolved NO3-N concentrations. Since farmers harvest more P in crops than they apply in fertilizer, the relatively high groundwater PO4-P values reflect the high native P content of Delta soils.