Effect of scale on the behavior of atrazine in surface waters

Field runoff is an important transport mechanism by which agricultural pesticides, including atrazine, move into the hydrologic environment. Atrazine is chosen because it is widely used, is transported in runoff relatively easily, is widely observed in surface waters, and has relatively little loss in the stream network. Data on runoff of atrazine from experimental plot and field studies is combined with annual estimates of load in numerous streams and rivers, resulting in a data set with 408 observations that span 14 orders of magnitude in area. The load as a percent of use (LAPU) on an annual basis is the parameter that is compared among the studies. There is no difference in the mean or range of LAPU values for areas from the size of experimental field plots (???0.000023 ha) and small watersheds (