PREDICTED AND MEASURED LEVELS OF AZINPHOSMETHYL IN THE LOURENS RIVER, SOUTH AFRICA : COMPARISON OF RUNOFF AND SPRAY DRIFT

The aim of the present study is to compare spray drift and runoff as routes of nonpoint-source azinphosmethyl pollution of the Lourens River based on predicted and measured values. existing predictive approaches were implemented using a geografical information system and validated using mezsured loads from subcatchment of the Lourens River. The ultimate comparison of runoff and spray drift was done at catchment level by comparing the results of the validated geografical information system models with measurements of pesticide loads from the filed during spray drift and runoff evnts. Finally, the importance of spray drift and runoff at the catchment level was compared on an annual basis using long-term meteorological data and average application characteristics.