Effects and empirical critical loads of nitrogen for ecoregions of the United States

Abstract

Human activity in the last century has led to a significant increase in nitrogen (N) emissions and deposition (Galloway et al. 2004). Total N emissions in the United States have increased significantly since the 1950s (Galloway 1998, Galloway et al. 2003). As S deposition has declined in response to regulation, the rate of N deposition relative to S deposition has increased since the 1980s (Driscoll et al. 2001, 2003) followed by a general decrease in NO_x emissions from electric utilities since the early 2000s. More recently, the relative proportion of NH_x (NH₄⁺ + NH₃ ) to NO_x (NO + NO₂) emissions has also increased for many areas of the United States (Kelly et al. 2005; Lehmann et al. 2005).

Citation

Pardo, Linda H.; Robin-Abbot, Molly J.; Fenn, Mark E.; Goodale, Christine L.; Geiser, Linda H.; Driscoll, Charles T.; Allen, Edith B.; Baron, Jill S.; Bobbink, Roland; Bowman, William D.; Clark, Christopher M.; Emmett, Bridget; Gilliam, Frank S.; Greaver, Tara L.; Hall, Sharon J.; Lilleskov, Erik A.; Liu, Lingli; Lynch, Jason A.; Nadelhoffer, Knute J.; Perakis, Steven J.; Stoddard, John L.; Weathers, Kathleen C.; Dennis, Robin L. 2015. Effects and empirical critical loads of nitrogen for ecoregions of the United States. In: de Vries, W.; Hettelingh, J.-P.; Posch, M., eds. Critical loads and dynamic risk assessment. Dordrecht, The Netherlands: Springer: 129-169. Chapter 5.