PESTICIDES IN RUNOFF - MEASUREMENT, MODELING, AND MITIGATION

Agricultural pesticide runoff has been investigated at four scales: la boratory research on processes, microplot and mesoplot studies under s imulated rainfall, and field/watershed studies under natural rainfall. Because rainfall and hydrology may be controlled, the intermediate sc ales (meso- and microplots) are becoming accepted techniques for effic iently estimating the risk of runoff of a pesticide as a function of w eather, soil, pesticide properties and cropping practice, and as a way to calibrate simulation models. The prediction desired-the probabilit y distribution of both chronic and acute levels of pesticides in aquat ic ecosystems and drinking water sources-depends on a large number of interacting processes and state variables. A complex computer simulati on model is required to sort out the possibilities and to define the m ost important controlling factors. Thus, runoff experiments at differe nt scales and model development and validation are mutually dependent enterprises.