Shifts in the Composition of Nitrogen Deposition in the Conterminous United States are Discernable in Stream Chemistry.
This paper evaluates the relationships between recent shifts in the form (oxidized vs. reduced) of N deposition and watershed and stream chemistry by coupling estimates of N deposition with stream measurements from the U.S. EPA National Rivers and Streams Assessment (NRSA; three stream surveys between 2000-2014) to evaluate the influence of changing atmospheric deposition on associated stream chemistry. It uses a recent fine-scaled N input inventory to identify watersheds where atmospheric deposition is the largest and assesses the temporal shift from a greater proportion of sites dominated by oxidized N deposition to a greater proportion of sites dominated by reduced N deposition. This shift in oxidized to reduced N deposition is highly relevant to the relationship between emissions reductions and ecosystem response and to improving characterization of the ecological effects of N deposition in the Integrated Science Assessments (ISAs).