Abstract
The Export Coefficient Model was modified to generate watershed-weighted maps of phosphorus export coefficient loads based on terrain and land cover map-derived estimates of runoff and buffering likelihood. Using the model, nonpoint-source critical areas were identified by setting P loading thresholds to local disproportionate sources. Modification of the Export Coefficient Model incorporated basic watershed-contributing area and dispersal area physical principles. The contributing area and dispersal area nutrient runoff theory, which holds that runoff and associated pollutant loading from a watershed is controlled strongly by its landscape position, run on from upslope contributing areas, and nutrient trapping opportunities within the runoff pathway, is presented, along with its use of uncertainty modeling. The contributing area and dispersal area Export Coefficient Model was applied to the West Branch Delaware River watershed, NY. Results revealed that the spatially distributed contributing area and dispersal area estimates matched the general trend in critical nonpoint-source area field observations.