Atrazine and nitrate transport to the Brazos river floodplain aquifer
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The potential for contamination of groundwater and surface water from agricultural chemicals used on river floodplains is a serious concern in many parts of the United States. An agricultural research site located near College Station, Texas, was instrumented to determine the fate of agricultural chemicals typically applied to the Brazos River floodplain. Nine well nests were installed in a 3x3 grid pattern, parallel and perpendicular to the river. Each well nest has four monitoring wells screened at various depths throughout the aquifer. Ammonium-nitrate fertilizer and the herbicide atrazine were applied to this research site at the time a corn crop was planted in 1994 and 1995. Groundwater and river samples were periodically collected and tested for nitrate-N, ammonium-N, and atrazine. Increases in nitrate-N in the groundwater were not observed due to high background concentrations of nitrate-N. Ammonium-N was not detected in the groundwater above background concentrations (<1 mg/L) due to nitrification of ammonium-N to nitrate-N in the clay soil. Atrazine was detected in the groundwater 24 days after the second application indicating preferential flow through the Ships clay surface layer that was 6 m thick. A pump test that was conducted at the research site just after the second atrazine application facilitated the movement of atrazine to a depth of 18 m.
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Chakka, K. B., & Munster, C. L.
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