|Blanchard, Paul - MO DEPT OF CONSERVATION|
Submitted to: Symposium on the Fate and Chemistry of Modern Pesticides Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2004
Publication Date: August 16, 2004
Citation: Lerch, R.N., Blanchard, P.E. 2004. Herbicide contamination and transport in northern Missouri and southern Iowa streams. Proceedings of the Symposium on the Fate and Chemistry of Modern Pesticides, August 16-19, 2004, Vail, CO. p. 56. Technical Abstract: In the Corn Belt region of the United States, herbicide contamination of streams is widely recognized as one of the major environmental impacts of row crop production. However, there remains a gap in our knowledge regarding watershed vulnerability to herbicide transport and assessment of herbicide loads from specific regions within the Corn Belt. The primary objectives of this study were: 1) to document herbicide occurrence and transport from watersheds in the northern Missouri/ southern Iowa region in an effort to quantify watershed vulnerability to herbicide transport; and 2) to compute the contribution of this region to the herbicide load of the Missouri and Mississippi Rivers. Grab samples were collected under baseflow and runoff conditions at 21 hydrologic monitoring stations between April 15 and July 15 from 1996 to 1999. Samples were analyzed for commonly used soil-applied herbicides and selected herbicide metabolites. Estimates of herbicide load and relative losses were computed for each watershed. Overall, occurrence of herbicides and metabolites in streams was related to herbicide usage, analytical detection limits, and stream discharge. Median parent herbicide losses, as a percentage of applied, ranged from 0.33 to 3.9%; loss rates that were considerably higher than other areas of the United States. Watershed vulnerability to herbicide transport, measured as herbicide load per treated area, showed that the runoff potential of soils was a critical factor affecting herbicide transport. Herbicide transport from these watersheds contributed a disproportionately high amount of the herbicide load to both the Missouri and Mississippi Rivers. Based on these results, this region of the Corn Belt is highly vulnerable to hydrologic transport of herbicides from fields to streams, and it should be targeted for implementation of management practices designed to reduce herbicide losses in surface runoff.