A newly published report by the U.S. Forest Service Southern Research Station shows that soil conditions in two Western North Carolina wilderness areas will keep improving over the next century as a result of continued reductions in air pollution resulting from the implementation of the Clean Air Act and other ongoing air pollution emission reductions. The research has implications for other high elevation areas in the Southern Appalachians.
Sulfur dioxide and nitrogen oxides are both major air pollutants produced by combustion that react with water molecules in the air to produce the “acid rain” that enters soils and pollutes surface waters. In forest soils affected by acid deposition, essential nutrients can be depleted, resulting in conditions that damage entire watersheds. Sulfur dioxide and nitrogen oxide emissions have sharply declined as a result of the Clean Air Act as well as other regulatory controls adopted over the last decades, but the effects of almost a century of pollution remain in forest soils.
To forecast improvement in forest soils in relation to gains in air quality over the next century, Katherine Elliott, research ecologist at the SRS Coweeta Hydrologic Laboratory, and co-authors Jim Vose and Bill Jackson simulated the effects of future levels of sulfur and nitrogen deposition on the Linville Gorge and Shining Rock Wildernesses, comparing current levels to five different possible levels of reduction from current levels. The researchers chose the two North Carolina wilderness areas because they are high elevation acidic cove forests growing in geologic conditions known to be sensitive to acidic deposition.
“Both wilderness areas contain areas where acid deposition has caused depletion of important soil-based nutrients as well as the mobilization of toxic substances such as aluminum,” says Elliot. “In some places, this has resulted in stream conditions that are unsuitable for the survival of many fish and other aquatic species.”
The five sulfur dioxide and nitrogen oxide deposition scenarios the researchers used are based on results developed in 2011 by the Visibility Improvement State and Tribal Association of the Southeast (VISTAS). For each of the five scenarios, the researchers simulated a 90-year period to forecast years 2010 to 2100. The simulations showed continued soil improvements under all scenarios, but the further reductions of scenario 5—where sulfur dioxide is reduced by 78 percent and nitrogen oxide by 52 percent—will be needed to improve compromised stream conditions to the point where they will once again support native brook trout and other aquatic species.
The findings have implications for other high elevation areas in the Southern Appalachians. “Land managers need to understand that there is a possibility that other areas like the two in this study may not fully recover within a desired time period, even with additional reductions in acidic deposition,” says Elliot. “Acidic forests in the region should be considered for restoration with nutrient supplements such as liming in order to move towards healthier ecosystems.”
For more information, email Katherine Elliott at firstname.lastname@example.org .