Use of indexes for evaluating potential of nonpoint source pollution in two agriculture watersheds

Water pollution from agriculture is becoming an acute problem. One of the solutions is to tackle the problem at the watershed scale. However, this can not be done without management tools to evaluate the effect of agricultural practices on water quality. The objective of this study was to assess a distributed indicator method for predicting the potential for sur-face water pollution. Water quality at the outlet of two watersheds, where animal production is dominant, was monitored on a continuous basis between March 1994 and February 1995. A geographical information system was used to compile spatial data needed by the indicator method and to perform elementary taks. Observed water quality was related to land use, particularly the intense animal production. Ammonium, total phosphorus, dissolved oxygen and fecal colimorms were parameters most affecting surface water quality. Differences were noticed between observed water quality and that predicted by the method of agricultural nonpoint source potential pollution indicators. These differences might be due to neglecting some nutrient and sediment transport processes. However, the method allowed the identification of zones, within each watershed, that could contribute more to water pollution.