SUSCEPTIBILITY OF INDIANA WATERSHEDS TO HERBICIDE CONTAMINATION

Using herbicide concentration data from 16 USGS monitoring stations throughout Indiana, the potential of two simple tools for predicting watershed susceptibility to herbicide contamination were evaluated. They were a simple index based on a regression of one or more factors, but focusing on factors known to affect runoff, and the process-based model, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS). Five herbicides were selected for study: alachlor, atrazine, cyanazine, metolachlor, and simazine. Results showed that the runoff curve number, alone or in combination with a chemical-use index, had the strongest correlation with herbicide concentrations of the variables and models tested. No relationship was noted between herbicide concentrations and tillage practices, slope, or watershed size.