Occurrence of Herbicides in Central Indiana Streams

Abstract

Agricultural chemicals, such as pesticides and herbicides, play an important role in agricultural operations to control unwanted pests and maximize crop yield. However, these chemicals may also threaten aquatic life. The abundance of agricultural chemicals, specifically atrazine and metolachlor, was measured in eighteen headwater streams of the Upper White River Watershed (UWRW) of central Indiana. Sites were selected to represent a range of agriculture activity within the watershed. Sites were sampled seasonally over one year (N54) to assess temporal variation in herbicide abundance and the influence of physiochemical factors. Pearson correlation coefficients were used to assess independent variables influencing stream herbicide concentrations. All sites had measurable concentrations of atrazine and metolachlor during June 2010 sampling; no herbicides were above the detection limit in August; only two sites had measureable concentrations of metolachlor in November; and, one site had measurable concentrations of atrazine and metolachlor in May. These data indicate concentrations of atrazine and metolachlor in central Indiana streams are temporally variable, being highest in late spring. Concentrations measured were comparable to other studies in agricultural areas and frequently exceeded concentrations known to have adverse effects on aquatic organisms.