Land cover as a framework for assessing risk of water pollution

A survey of numerous field studies shows that nitrogen and phosphorous expo rt coefficients are significantly different across forest, agriculture, and urban land-cover types. We used simulations to estimate the land-cover com position at which there was a significant risk of nutrient loads representa tive of watersheds without forest cover. The results suggest that at betwee n 20 percent and 30 percent nonforest cover, there is a 10 percent or great er chance of N or P nutrient loads being equivalent to the median values of predominantly agricultural or urban watersheds. The methods apply to envir onmental management for assessing the risk to increased nonpoint nutrient p ollution. Interpretation of the risk measures are discussed relative to the ir application for a single watershed and across a region comprised of seve ral watersheds.