Assessment of predictors for stream eutrophication potential

Predicting stream eutrophication potential from nonpoint source nutrient lo ading across large temporal and spatial scales is a significant problem. In this paper we describe how two physiological indicators of P stress of str eam biofilms, alkaline phosphatase activity (APA) and stored (surplus)P rel ate to two predictors of P loading: annual P loading predicted by the water shed model SIMPLE, and stream concentrations of soluble reactive P (SRP) in eight subbasins in the Illinois River basin in Oklahoma. Data for APA, sur plus P, nutrients and water chemistry were obtained at watershed outlets on ce during the cold season and twice during the warm season. There was a neg ative curvilinear relationship between APA and both predictors. Best fit wa s achieved by APA vs. annual predicted P loading. Both SRP and P-load are p otentially useful to identify subbasins requiring no pollution abatement an d to establish a regional target for P-load reduction. Surplus P is not as useful as APA in establishing these thresholds.