Water Quality Priority Zone (Draft - 2014)

In order to identify areas within the Mississipi River Basin (MRB) where implementing wildlife conservation actions could potentially provide the highest benefit to both local waters and the Gulf of Mexico the Miss. River Basin/Gulf Hypoxia Initiative identified a "Water Quality Priority Zone". This provisional zone of interest represents HUC-8 watersheds having the highest potential for nutrient export from agricultural sources (using nitrogen as a surrogate). The potential for nutrient export was determined using the 2002 SPARROW Mississippi/Atchafalaya River Basin Model and cropland data from the 2013 USDA-NASS Cropland Data Layer. As the results from the SPARROW model are somewhat dated (ca. 2002), we incorporated HUC-8 watersheds with high proportions of cropland as a surrogate for high nutrient export. This is particularly important considering the wholesale conversion of CRP lands to cropland over the past decade or so. The Water Quality Priority Zone contains any HUC-8 watershed with at least 308 kg/m2/year of nitrogen loading attributed to agricultural sources in the 2002 SPARROW Mississippi/Atchafalaya River Basin Model or containing at least 39% cropland as identified in the 2013 Cropland Data Layer. The SPARROW threshold represents the top 40th percentile of values, while the cropland proportion represents the top 20th percentile of values. These thresholds were selected somewhat subjectively with the goal in mind of selecting an area that was small enough to be manageable, yet large enough to contain a representative set of landscape conditions.