ATRAZINE IN SPRING RUNOFF AS RELATED TO ENVIRONMENTAL SETTING IN NEBRASKA, 1992

A synoptic sampling of five surface-water sites in central Nebraska wa s conducted by the U.S. Geological Survey as part of its National Wate r-Quality Assessment Program during storm runoff in May 1992 to relate transport, yields, and concentrations of atrazine to environmental se tting. Atrazine was the most extensively applied pesticide in the stud y unit. Atrazine transport was related to the size of contributing dra inage area, quantity of atrazine applied, amount of precipitation, and volume of streamflow. Estimated yields and mean concentrations of atr azine were related to the percentage of cropland in a drainage area. T he largest estimated yields and mean concentrations of atrazine in sur face water were associated from drainage areas with the highest percen tage of cropland, and the smallest was associated with the smallest am ount of cropland. Atrazine concentrations increased as streamflows, in creased but decreased at or near the time of peak streamflows, perhaps due to dilution. Atrazine concentrations then increased and remained elevated far into the stream recession. Atrazine is a regulated contam inant in finished public-water supplies. Large concentrations of atraz ine could affect the management of public-water supplies because atraz ine remains in solution in contrast to many other pesticides that are more easily removed.