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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #231397
Title: Herbicide transport in Goodwater Creek experimental watershed: I. long-term research on atrazine

Author
item Lerch, Robert
item Sadler, Edward
item Sudduth, Kenneth - Ken
item Baffaut, Claire
item Kitchen, Newell

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2010
Publication Date: 12/6/2010
Citation: Lerch, R.N., Sadler, E.J., Sudduth, K.A., Baffaut, C., Kitchen, N.R. 2010. Herbicide transport in Goodwater Creek experimental watershed: I. long-term research on atrazine. Journal of the American Water Resources Association. 47(2):209-223.

Interpretive Summary: Atrazine continues to be the herbicide of greatest concern relative to contamination of surface waters in the United States. However, a lack of long-term data hampers the detection of trends. The objectives of this study were to analyze trends in atrazine concentration and mass transported in the Goodwater Creek Experimental Watershed 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 (USEPA). Located within the Central Claypan Region of northeastern Missouri, the watershed encompasses 77 km**2 (28 sq miles) of predominantly agricultural land uses, with an average of 21% of the watershed in corn or sorghum, the two crops that receive the most atrazine treatment. Water samples were collected at weekly intervals and for every runoff event. Results of the study showed that corn acreage and atrazine use in the watershed increased by about 28% from 1992 to 2006. However, no trends in stream atrazine concentration were apparent. Observed trends in the daily mass of atrazine transported were mainly tied to changes in stream flow. Yearly, from less than 1% to 14% of the atrazine applied within the watershed was lost from the outlet, with a middle value of about 6%. Year-to-year differences in atrazine loss were more associated with timing of runoff events after atrazine application than with size of the runoff events. Atrazine reached concentrations that may be harmful to aquatic ecosystems in 10 out of 15 years, and concentrations typically exceeded the U.S. Environmental Protection Agency (USEPA) screening criteria for several days to weeks each year. Because the atrazine ecological criteria established by the USEPA were exceeded, atrazine manufacturers will be required to work with farmers in the watershed to implement practices that reduce atrazine transport. This research has been beneficial to state and federal regulatory agencies charged with the task of identifying impaired waterways, and it has also been beneficial to the USEPA in their efforts to identify areas of the Corn Belt most vulnerable to atrazine contamination of streams. In addition, farmers will benefit as the main manufacturer of atrazine will need to work with farmers to implement practices to reduce atrazine transport. By avoiding an impaired waterway designation for Goodwater Creek watershed, farmers will be able to continue using atrazine for weed control.

Technical Abstract: Atrazine [6-chloro-N2-ethyl-N4-(1-methylethyl)-1,3,5-triazine-2,4-diamine] continues to be the herbicide of greatest concern relative to contamination of surface waters in the United States. However, a lack of long-term data hampers the interpretation of cause-effect relationships and the detection of trends. The objectives of this study were to analyze trends in atrazine concentration and load 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 (USEPA). Located within the Central Claypan Region of northeastern Missouri, GCEW encompasses 72.5 km**2 of predominantly agricultural land uses, with an average of 21% of the watershed in corn (Zea mays) or sorghum (Sorghum bicolor). Flow-weighted runoff and weekly baseflow grab samples were collected from 1992 to 2006 at the outlet to GCEW and analyzed for atrazine. Cumulative frequency diagrams and correlation analyses showed no significant time trends for atrazine concentration. Observed trends in daily load were mainly a function of trends in stream discharge. Relative annual loads varied from 0.56 to 14% of the applied atrazine, with a median of 5.9%. Annual variation in loads was a function of the timing of runoff events relative to atrazine application within the watershed, and the magnitude of runoff events was a much less important factor to atrazine transport. Atrazine reached concentrations considered harmful to aquatic ecosystems in 10 out of 15 years, and concentrations typically exceeded the USEPA screening criteria for days to weeks each year. Because the atrazine ecological criteria established under the USEPA interim re-registration eligibility decision have been exceeded, atrazine registrants will be required to work with farmers in the watershed to implement practices that reduce atrazine transport.