Influence of acidic atmospheric deposition on soil solution composition in the Daniel Boone National Forest, Kentucky, USA

Soil solution chemistry provides insight into element cycling, nutrient uptake and availability, mineral transformation, and pollution transport processes within the subsurface environment. Therefore, chemical analysis of the extractable soil water fraction has been utilized in several studies to assess the condition of ecological resources and to identify stresses, and levels thereof, which may be contributing to ecosystem deterioration (Karathanasis 1989; Lawerence and David 1996; Kaiser and Kaupenjohann 1998). The composition of the soil solution as an index of potential Al toxicity and soil acidification from anthropogenic processes has been used extensively and has been instrumental in the development of models for simulating the effects of acidic deposition on soil and water systems (Cosby and others 1985; Reuss and Johnson 1986; Johnson 1995). However, the mechanisms dictating solubility control of different species within the solution phase and how they influence soil acidification are sitespecific and remain a topic of debate. The acidification of water in the atmosphere is typically controlled by carbon dioxide equilibrium in the presence of naturally derived nitric and sulfuric acids. These natural background constituents, however, rarely result in rainwater pH levels below 5.0 and are generally contained in the area of their formation (Spiro and Stigliani 1996). The combustion of fossil fuels, primarily coal and oil, may increase the levels of SOz and NO, in the atmosphere and contribute to significant lowering of rainwater pH levels (National Acid Precipitation Assessment Program 1987). In addition, the area of impact from these emissions can