Citation:

Lassiter, Meredith, J. Lin, J. Compton, J. Phelan, R. Sabo, J. Stoddard, S. McDow, AND T. Greaver. Shifts in the Composition of Nitrogen Deposition in the Conterminous United States are Discernable in Stream Chemistry. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 881:163409, (2023). https://doi.org/10.1016/j.scitotenv.2023.163409

Impact/Purpose:

The purpose of this sub-product (manuscript) is to communicate findings on a project examining nitrogen deposition trends to watersheds, and subsequent stream chemistry response. The composition of N deposition is changing across the U.S., reduced N is now equivalent to oxidized N when deposition is averaged across the entire nation and, in some areas, reduced N dominates deposition. This is primarily due to the Clean Air Act Amendments of 1990 and other air quality regulations that have resulted in declining deposition of oxidized forms of N. This project is significant in that it examines shifts in the form of nitrogen at the national scale and for three time periods (between 2000 and 2014) using data from the EPA National Aquatic Resource Surveys (for rivers and streams) and National Atmospheric Deposition Program (NADP) Total Deposition (TDEP) data to elucidate deposition trends impacting waterbodies. This information could have a broad impact in terms of consideration of the effects of changing deposition, especially stream chemistry response to these long-term changes in composition of atmospheric nitrogen inputs.    

Description:

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).

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