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3.2 Acid Deposition Methodology: Future Predictions

Sulfur deposition is a primary contributor to acid deposition that indirectly affects forest decline by leaching base cations from the soil. Therefore, in 1990, Title IV of the Clean Air act set as its primary goal the reduction of annual SO₂ emissions by 10 million tons below 1980 levels (U.S. EPA 1997a). To achieve these reductions by 2010, the law invoked a restriction on power plants fired with fossil fuels. By 1995, nationwide emissions of SO₂ were reduced by almost 40 percent below their required level. In addition, monitoring sites throughout the United States found statistically significant reductions in precipitation acidity and sulfate concentrations (NAPAP 1998). Attempts to reduce nitrogen deposition were initiated in 1996. Although Title IV initiated a reduction in annual nitrogen deposition, new concentrations are expected to have potential impacts on forests across the South. Modeling future projections and impacts of nitrogen and sulfur deposition on forested ecosystems in the Southern Appalachian Mountains is an ongoing research objective of the Southern Appalachian Mountains Initiative (SAMI).