Assessing Phosphorus Risk Using GIS in a Mountain Watershed.

Phosphorus Risk Indices have been widely used to prioritize land areas where management practices for water quality improvement have highest priority. While most frequently used at individual field sites, some watershed scale applications of P Risk Indices have been performed. In this study, we used data available in public geodatabases to calculate P risk on a mixed use mountain watershed. We compared the predicted risk scores to risk calculated from individual sites throughout the watershed. The results showed that snowmelt runoff created the greatest risk of P transport, even on shrub lands with high native soil P. Winter livestock feeding was a managment practice associated with P runoff risk in snowmelt.  The P Index does not account for irrigation diversions and groundwater-surface water interactions that are of known importance in the watershed.