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United States Department of Agriculture

Agricultural Research Service

Title: Agrichemical Transport to Ground Water in a Sandy Coastal Plain Soil

item Bosch, David
item Truman, Clinton

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2002
Publication Date: October 1, 2002

Interpretive Summary: While the protection of all water resources is important, the protection of ground water is particularly critical because it is often used as a drinking water source. Elevated pesticide and nitrogen concentrations in ground water have been traced back to agricultural management at the land surface. To prevent excess transport of agrichemicals to ground water it is necessary to fully understand the mechanisms through which they are transported from the ground surface to the water table. A four-year study was undertaken to examine the timing and magnitude of agrichemical transport into ground water in a sandy aquifer recharge area in central Georgia, USA. Conventional practices on a summer corn and winter wheat rotation were examined. Monthly soil-water and groundwater samples indicated that while field management practices were impacting the local ground water, the elevated groundwater concentrations observed below the field did not persist as the groundwater moved down gradient. While elevated nitrate and pesticide concentrations were observed in ground water below the field, they were generally below national health advisory levels. During the observation period, groundwater contamination was driven by large precipitation events. This study indicates that it is important to gage field management to climatic conditions to reduce the likelihood of groundwater contamination.

Technical Abstract: Monitoring data developed by the State of Georgia show widespread violations of water quality standards in the Suwannee River Basin due to low dissolved oxygen (DO). TMDL modeling for the impaired streams indicates an average 40% load reduction for Total N and Total P is necessary to relieve the DO impairment. These estimates assume nutrient enrichment is causing excessive algal growth that leads to depleted DO. Because many of the impaired streams do not have point source discharges, these load reductions will need to come from reductions in nonpoint sources, primarily agriculture and silviculture. The GA DNR-Environmental Protection Division sets standards for the various designated uses of the states's surface waters. For fishing, which is the designated use of most rivers in the Georgia Coastal Plain, the DO standard is an average of 5.0 mg L-1 or a minimum of 4.0 mg L-1. Dissolved oxygen data have been collected at 21 sites in three watersheds in South-central Georgia for fou years. DO concentrations observed from 1997 to 2001 ranged from 0.4 mg L-1 to 20.8 mg L-1. Six measurement sites were found to be below state standards for streams supporting fish. Statistical correlations between DO and other measured parameters, including temperature, pH, conductivity, oxidation-reduction potential, turbidity, and flow depth, were poor. However, there was some indication that low DO levels coincided with periods of low flow. Additional data is necessary to evaluate these relationships and natural levels of DO in streams.

Last Modified: 4/18/2015
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