Agricultural Chemicals in the St. Joseph River Watershed

The St. Joseph River contributes a relatively small proportion of the flow to Lake Michigan, but the largest load of atrazine. High concentrations of both pesticides and nitrate are common in the ground water in both Michigan and Indiana, and ground water is the source of about 90 percent of the streamflow. Load-reduction goals set by State and Federal regulators may not be able to be met because of this combination of conditions -- the best management practices (BMPs) pertain to to surface-water runof from crops, not ground-water runoff. The goals also do not account for the much longer travel times associated with non-point-source pollution from ground water as compared to surface runoff.

This work, part of a larger project, involved collecting water quality samples at 19 sites within the St. Joe drainage in Indiana and Michigan to determine if the atrazine loading is spread uniformly over the basin, or is concentrated in one or more "hot spots." The results will help quantify loadings of selected agricultural chemicals and will be coupled with ground-water flow modeling and improved geologic mapping to provide residence times for those chemicals in the gorund-water system.

Friends of the St. Joe River Association