| Abstract
| - Field runoff is an important transport mechanism bywhich agricultural pesticides, including atrazine, moveinto the hydrologic environment. Atrazine is chosen becauseit is widely used, is transported in runoff relativelyeasily, is widely observed in surface waters, and hasrelatively little loss in the stream network. Data on runoffof atrazine from experimental plot and field studies iscombined with annual estimates of load in numerous streamsand rivers, resulting in a data set with 408 observationsthat span 14 orders of magnitude in area. The load as apercent of use (LAPU) on an annual basis is the parameterthat is compared among the studies. There is no differencein the mean or range of LAPU values for areas fromthe size of experimental field plots (≥0.000023 ha) andsmall watersheds (<100 000 ha). The relatively invariantLAPU value observed across a large range of watershedareas implies that the characteristics of atrazine itself(application method and chemical properties) are importantin determining the extent of runoff. The variable influenceson the extent of runoff from individual watershedcharacteristics and weather events are superimposed onthe relatively invariant LAPU value observed across therange of watershed areas. The results from this study establishthe direct relevance for agricultural field plot studies towatershed studies across the full range of scale.
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