Herbicide Distribution and Variability Across Goodwater Creek Watershed in North Central Missouri
- W. W. Donald *,
- A. T. Hjelmfelt and
- E. E. Alberts
One objective of the Missouri Management Systems Evaluation Area was to monitor and assess surface water quality, including spatial and temporal variability in herbicide concentrations within the 7250 ha Goodwater Creek Watershed. Stream water was sampled at all stream-road intersections across the watershed on 10 occasions in 1993 and 1994. Maps of herbicide distribution established that widespread, seasonal contamination of streams in Goodwater Creek Watershed was due to nonpoint sources (e.g., widespread, but normal farm use) rather than from point sources. Box plots documented concentration variability over time. Concentrations of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), deethylatrazine [2,4-diamino-6-chloro-N-(1-methylethyl)-1,3,5-triazine], deisopropylatrazine [2,4-diamino-6-chloro-N-ethyl-1,3,5-triazine], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were also monitored at least weekly from 1993 to 1994 at three V-notch weirs through which 16.7, 43.4, and 100% of the watershed drained. Atrazine, deethylatrazine, and metolachlor were detected year round at concentrations above 0.1 µg/L. Atrazine concentrations observed at weirs were occasionally >100 µg/L and were similar to edge-of-field concentrations observed elsewhere shortly after spraying in May to June, probably because the watershed's poorly drained, silt loam soils contain a restrictive claypan horizon that limits infiltration and encourages surface runoff.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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