Recent advances in critical loads research from the US EPA Office of Research and Development
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Nitrogen and sulfur deposition have declined dramatically since peaking in the 1980s and 1990s in the U.S., yet many areas still receive atmospheric deposition in excess of known thresholds for ecological harm, termed “critical loads.” Years of collaborative research between the EPA, National Park Service, US Forest Service, and various universities and companies have yielded a wealth of information on critical loads for various ecosystems and taxonomic groups. This presentation will provide an overview of some of the more recent advances from the US EPA Office of Research and Development. Specifically, we will discuss four atmospheric deposition projects: (1) extending the point-estimate herbaceous critical loads for richness (Simkin et al. 2016) and individual species (Clark et al. 2019) to the CONUS, and extensions of tree species critical loads (Horn et al. 2018) to include (2) ozone, (3) regional variation in the sensitivity to N and S deposition, and (4) additional mechanistic drivers. Finally, we will discuss extensions to these approaches to examine species-level sensitivity to climate change. In total this work helps improve our understanding of the vulnerability of forest and herbaceous ecosystems to various environmental stressors, to try and inform local and regional environmental management.