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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #148060
Title: WATERSHED VULNERABILITY TO HERBICIDE TRANSPORT IN NORTHERN MISSOURI AND SOUTHERN IOWA STREAMS

Author
item Lerch, Robert
item BLANCHARD, PAUL - U OF MO

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2003
Publication Date: 12/15/2003
Citation: Lerch, R.N., Blanchard, P. 2003. Watershed vulnerability to herbicide transport in northern Missouri and southern Iowa streams. Journal of Environmental Science and Technology. 37:5518-5527.

Interpretive Summary: In the Corn Belt region of the U.S., herbicide contamination of streams is widely recognized as one of the major environmental impacts of row crop production. If we understand the factors that cause a watershed to be vulnerable, then we can prioritize our limited conservation resources on those watersheds that contribute most to the problem. The objectives of this study were to document herbicide occurrence and transport from watersheds in the northern MO/southern IA region in an effort to quantify watershed vulnerability to herbicide transport and to compute the contribution of this region to the herbicide load of the Missouri and Mississippi rivers. Water samples were collected from 20 streams and one reservoir in MO and IA between Apr 15 and July 15 from 1996 to 1999. These 21 sites drain a total of about 20,000 sq. miles of the southern Corn Belt. Samples were analyzed for 6 commonly used soil-applied corn and soybean herbicides and 4 herbicide metabolites. In general, these 10 compounds were present in >90% of all samples collected, and median concentrations were similar to or higher than other areas of the Corn Belt. 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 U.S. In addition, herbicide transport from these watersheds contributed a disproportionately high amount of the herbicide load to both the Missouri and Mississippi rivers. This region of the Corn Belt is highly vulnerable to transport of herbicides because of the poorly drained, runoff prone soils that are common to much of this region. This work will benefit state and federal agencies that must prioritize which watersheds should be targeted for BMP implementation to meet Total Maximum Daily Load regulations or should receive conservation program funds under the 2002 Farm Bill.

Technical Abstract: In the Corn Belt region of the U. S., 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 to document herbicide occurrence and transport from watersheds in the northern MO/southern IA region in an effort to quantify watershed vulnerability to herbicide transport and 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 Apr 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 U. S. 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.