Nitrogen and sulfur deposition have declined in the eastern U.S. since the 1980s and 1990s following the 1990 Amendments to the Clean Air Act, yet they remain significantly elevated above thresholds where sensitive ecological end points are affected. Here we summarize several projects on assessing ecosystem sensitivity to N and S deposition, and the ecosystem services affected. One focus of the talk is on forest health and biodiversity, and here we use recently available critical loads for 94 tree species to examine how individual tree species are affected across the conterminous U.S. We also explore methods for synthesizing this information to inform development of air quality policies under the secondary standards of the NAAQS.

The views expressed here are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency.