PARTNERS: USDA Forest Service Southern Research Station, E & S Environmental

SUMMARY: Numerous research studies have shown that nitrogen, sulfur, and ozone pollutants reduce forest growth, degrade soils, damage lake and stream water quality, alter biodiversity, and increase forest mortality. Despite this knowledge and significant investments to reduce or mitigate negative pollution effects, policy makers and regulators have no easy means by which to judge the sensitivity of U.S. ecosystems to important air pollutants. Critical load, defined as the level of a pollutant above which an ecosystem experiences detrimental effects, is a metric that can be used for this purpose. This study proposes to develop a national map of critical pollutant loads for nitrogen and sulfur, following the leads of Canada and European nations. Previous critical load mapping studies do not account for the combined influence of multiple pollutants (e.g., nitrogen and ozone) or the impact of non-critical load stresses (e.g., drought, insect, or disease) on forest ecosystem health. A systematic assessment of coarse scale national level and fine scale special interest area critical load projections is proposed in this five phase study plan. The five phases include: 1) a coarse resolution critical load map for the continental U.S. using an existing Simple Mass Balance (SMB) critical load model and existing synoptic-scale data for soils, geology, climate, and other pertinent factors; 2) site-specific critical load maps, also derived from the SMB, for special interest areas, including sites with long-term records such as Coweeta Hydrologic Laboratory, special use areas such as Clean Air Act mandatory federal class one areas, USDA Forest Service critical load prototype sites, and areas with high pollutant deposition such as the Fernow Experimental Forest; 3) an examination of the relationship between coarse and fine scale critical load maps at overlapping areas with an emphasis on spatial sensitivity analysis; 4) an uncertainty analysis aimed at identifying the variability in environmental factors exerting the greatest influence on critical load estimates and developing confidence intervals around critical load predictions; and 5) an evaluation of the SMB with regard to non-pollutant stress (e.g., climate, insects, fire, and disease) impacts. A review of previous accomplishments and discussion of future research will follow the completion of the final phase. 

STATUS: Ongoing

PROGRESS: Researchers are examining critical acid loads in streams at a continental scale.

Paoletti Elena, Andrzej Bytnerowicz, Chris Andersen, Algirdas Augustaitis, Marco Ferretti, Nancy Grulke, Madeleine S. Günthardt-Goerg, John Innes, Dale Johnson, Dave Karnosky, Jesada Luangjame, Rainer Matyssek, Steven McNulty, Gerhard Müller-Starck, Robert Musselman, and Kevin Percy. 2007. Impacts of Air Pollution and Climate Change on Forest Ecosystems: Emerging Research Needs. The Scientific World Journal 7(S1):1–8.

L. H. Pardo, P. H. Templer, C. L. Goodale, S. Duke, P. M. Groffman, M. B. Aadams, P. Boeckx, J. Boggs, J. Campbell, B. Colman, J. Compton, B. Emmett, P. Gundersen, J. Kjonaas, G. Lovett, M. Mack, A. Magill, M. Mbila, M. J. Mitchell, G. McGee, S. McNulty, K. Nadelhoffer, S. Ollinger, D. Ross, H. Rueth L. Rustad, P. Schaberg, S. Schiff, P. Schleppi, J. Spoelstra and W. Wessel. 2006. Regional assessment of N saturation using foliar and root δ¹⁵N. Biogeochemistry 80:143-171. (PDF)

Li, Harbin and Steven McNulty. 2007. Uncertainty analysis on simple mass balance model to calculate critical loads for soil acidity. Environmental Pollution 149: 315-326. (PDF)

Steve McNulty, Erika Cohen, Harbin Li, and Jennifer Moore Myers. 2007. Estimates of critical acid loads and exceedances for forest soils across the conterminous United States. Environmental Pollution 149: 281-292. (PDF)

LINKS:

USDA Forest Service Southern Research Station

E & S Environmental

CONTACT: Steve McNulty, EFETAC Southern Global Change Program Team Leader, steve_mcnulty@ncsu.edu or 919-515-9489