Land Cover as a Framework for Assessing the Risk of Water

A survey of numerous field studies shows that nitrogen and phosphorous export coefficients are significantly d@erent across forest, agriculture, and urban land-cover types. We used simulah’ons to estimate the land-cover composition at which there was a sigt$cant risk of nutrient loads representative of watersheds without forest cover. The results suggest that at between 20 percent and 30 percent non-forest cover, there is a 10 percent or greater chance of N or P nutrient loads being equivalent to the median values of predominantly agricultural or urban watershed. The methods apply to environmental management for assessing the risk IO increased nonpoint nutrient pollution. interpretation of the risk measures are discussed relative to their application for a single watershed and across a region comprised of several watersheds.