In watersheds, spatial variation in nutrient sources and sinks results in spatial variability of nutrient export ratios and nutrient forms, with important implications for surface fresh water and estuarine ecosystem response. However, past attempts to model global and regional nutrient exports to the coastal zone in a spatially explicit manner have generally ignored within-basin spatial variation in nutrient sources and sinks.  We describe, apply and evaluate a new continental-global scale model of dissolved inorganic phosphorus (DIP) transport by rivers called NEWS-DIP-Half Degree (HD), based on a DIP export model developed by the Global NEWS (Global (N)utrient (E)xport from (W)ater(S)heds) work-group.  This new model retains half-degree resolution of input variables in analysis and explicitly routes water and nutrients downstream through watersheds, accounting for both DIP sources and DIP sinks along major river systems. 

Results/Conclusions  
When NEWS-DIP-HD-based predictions are compared to measurements from US rivers, the predictive capacity of this model is similar to previously developed whole basin DIP export models (r² = 0.67 for modeled vs. measured DIP load; kg P basin^-1 yr^-1).  Early results show high rates of spatial variability with respect to DIP production and consumption, an important role for urban areas as DIP sources, a dominant role for humans (and specifically for point sources of P) in P loading to surface waters, and a significant role for reservoirs in storing and removing DIP as it flows across the landscape.