Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2014
Publication Date: 6/2/2014
Publication URL: http://handle.nal.usda.gov/10113/59724
Citation: Smiley, P.C., King, K.W., Fausey, N.R. 2014. Annual and seasonal differences in pesticide mixtures within channelized agricultural headwater streams in central Ohio. Agriculture, Ecosystems and Environment. 193:83-95.
Interpretive Summary: Knowledge of the impacts of pesticides on stream ecosystems is limited because it is based on what is known about individual pesticides, not the pesticide mixtures that commonly occur in streams. Previous research on pesticide mixtures has been limited to simple summaries of the occurrence of pesticide mixtures within large streams and rivers. A more complete evaluation of pesticide mixtures and their trends is needed to understand the exposure that the stream biota experience. We examined the complexity, concentration, and types of pesticide mixtures within channelized agricultural headwater streams in central Ohio. Key findings indicated that pesticide mixtures exhibit seasonal trends, but the trends differ annually. These results are novel because they represent the first comprehensive documentation of pesticide mixtures within agricultural headwater streams. The results are valuable for watershed managers because they provide empirical evidence that supports the need for designing watershed management plans that target the reduction of multiple pesticides.
Technical Abstract: Only a limited amount of information on pesticide mixtures within agricultural headwater streams is available. A greater understanding of the characteristics of pesticide mixtures and their spatial and temporal trends within agricultural headwater streams is needed to evaluate the risks of pesticide mixtures. We measured concentrations of thirteen pesticides within seven channelized agricultural headwater streams in central Ohio for five years to document what types of pesticide mixtures occur, trends in pesticide mixtures with increasing watershed size, and annual and seasonal trends in pesticide mixtures. Pesticide mixtures consisted mostly of combinations of herbicides or herbicides and fungicides. Only one of fourteen response variables differed between watershed sizes. Seasonal trends in the percent occurrence, complexity, concentration, and types of pesticide mixtures differed annually. Our results suggest channelized agricultural headwater streams with watershed sizes ranging from 0.7 to 4.5 km2 will exhibit greater temporal variation than spatial variation in pesticide mixtures.