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Application of pesticides within the watersheds of agricultural streams typically leads to increased instream pesticide concentrations that reduces water quality and threatens aquatic life. Pesticide reduction practices that reduce pesticide application within agricultural watersheds should reduce concentrations of pesticides within agricultural streams. Unfortunately, the influence of pesticide reduction practices on pesticides and the biota within agricultural headwater streams has not been empirically evaluated. We evaluated the watershed scale influence of atrazine reduction prac tices on pesticides, pesticide mixtures, and fish communities within channelized agricultural headwater streams in central Ohio. Water samples for pesticide measurements and fishes were collected in the spring and summer from a treatment stream (watershed size – 3.89 km 2 ) that received atrazine reduction practices within 26 to 31% of its watershed during the first two years and then the watershed usage of these practices was reduced to less than 6% in the last four years. We also collected water samples and fishes during the same time from a control stream (watershed size 4.54 km 2 ) that received atrazine reduction practices in 6% or less of its watershed during the study. Only three of 15 pesticide response variables and two of 15 fish community response variables indicated a potential effect of atrazine reduction practices. Mean differences in atrazine desethyl concentration, atrazine desethyl percent occurrence, and the number of pesticides between the control and treatment streams were greater during the time period with atrazine reduction practices than the time period without atrazine reduction practices. Mean differences in trophic guild richness and fish species composition simi larity between the control and treatment streams occurred between time periods with and without atrazine reduction practices only during the summer. Our results suggest that implementing atrazine reduction practices to reduce atrazine usage within small portions (30% or less) of the watersheds of channelized agricultural headwater streams may not influ ence pesticides, pesticide mixtures, and fish community struc ture during the spring and summer.

Influence of Watershed Scale Atrazine Reduction Practices on Pesticides and Fishes within Channelized Agricultural Headwater Streams