FACTORS AFFECTING PESTICIDE OCCURRENCE AND TRANSPORT IN A LARGE MIDWESTERN RIVER BASIN

Data are presented from a study, initiated in 1991, that examined the occurrence and transport of pesticides in the White River Basin, IN. Concentrations of acetochlor, alachlor, atrazine, butylate, cyanazine, metolachlor, and diazinon were determined and used to examine human and natural factors affecting the occurrence of the pesticides. The data show that concentrations were highest in late spring or early summer, and were a function of weather conditions prior to application and rainfall runoff patterns subsequently. More-persistent herbicides, such as alachlor and metolachlor, tended to be noted more often and at higher concentrations than less-persistent pesticides. The presence of butylate, diazinon, and atrazine was impacted not only by their regional patterns of use, but also by differences in the natural characteristics of the smaller basins in the larger White River Basin. Overall, the amount of agricultural herbicides transported by the river was a very small percentage of the total amount applied to cropland within the basin.