|Hjelmfelt Jr, Allen|
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 11/12/1996
Publication Date: N/A
Technical Abstract: The Missouri Management Systems Evaluation Area (MSEA) project deals with the transport of agrichemicals to ground and surface water within the 7250 ha Goodwater Creek Watershed in north-central Missouri. Within this watershed, 1-3 m of loess and up to 15 m of fractured pre-Illinoian glacial till comprise the glacial aquifer. The claypan (naturally-formed argillic soil horizon) limits recharge to the glacial aquifer and promotes surface water runoff. Near the creeks, the glacial deposits have been eroded, and the ground water flows into the alluvium. The average annual precipitation is 94.77 cm. The average annual streamflow exiting the watershed is 30.81 cm. Standard hydrograph separation techniques indicate that surface runoff accounts for 85% of the total streamflow. Herbicide concentrations in surface runoff and baseflow are much higher than in rainfall or in the glacial aquifer. The herbicides act as a tracer of the dynamics of ground water-surface water interchange within the alluvium. Herbicide concentrations in the stream peak each year during spring and early summer runoff events. Atrazine concentrations in Goodwater Creek baseflow frequently exceed 3 ppb from May to mid-summer. Herbicide concentrations in the rainfall and in the glacial aquifer are low. The floodplain is not cropped. High herbicide concentrations in the alluvium must be from infiltration of stream or upslope surface runoff water during runoff events. Thus the alluvial ground water is contaminated by surface runoff, and subsequent discharge of this contaminated ground water maintains elevated herbicide concentrations in the stream between runoff events.