Title: Herbicide Transport Trends in Goodwater Creek Experimental Watershed Authors
Submitted to: Interagency Conference on Research in the Watersheds
Publication Type: Abstract Only
Publication Acceptance Date: September 8, 2008
Publication Date: February 20, 2009
Citation: Lerch, R.N., Sadler, E.J., Sudduth, K.A., Baffaut, C. 2009. Herbicide Transport Trends in Goodwater Creek Experimental Watershed [abstract]. In: Interagency Conference on Research in the Watersheds, September 8-11, 2008, Estes Park, Colorado. p. 261. Technical Abstract: Hydrologic transport of soil-applied herbicides continues to be of great concern relative to contamination of surface waters in the United States. The objectives of this study were to analyze trends in herbicide concentrations and loads in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006, and to conduct a retrospective assessment of the potential aquatic ecosystem impacts caused by atrazine contamination using screening criteria established by the U.S. Environmental Protection Agency. Located within the Central Claypan Region of northeastern Missouri, GCEW encompasses 77 km2 of predominantly agricultural land uses, with an average of 21% of the watershed in corn or sorghum. Flow-proportional runoff and weekly baseflow grab samples were collected from 1992 to 2006 near the outlet to GCEW and analyzed for acetochlor, alachlor, atrazine, and metolachlor. Using cumulative frequency diagrams and correlation analyses, the results showed no significant time trends for atrazine concentration, but the other herbicides showed trends based on changes in use. Atrazine had the highest relative loads, with a median of 5.9% of applied lost annually. Variation in annual loads was a function of the timing of runoff events relative to herbicide application within the watershed, and the magnitude of runoff events was a much less important factor to transport. Atrazine reached concentrations that may be harmful to aquatic ecosystems in 10 out of 15 years, and concentrations typically exceeded the screening criteria for days to weeks each year. Pending inclusion of GCEW on the impaired waters list will officially require mitigation actions be taken to reduce atrazine concentrations, further highlighting the need to find cost-effective management alternatives that reduce the likelihood of atrazine transport and/or reduce atrazine inputs in GCEW.