Acidic deposition, ecosystem processes, and nitrogen saturation in a high elevation Southern Appalachian watershed

High-elevation red spruce-Fraser fir forests in the Southern Appalachian mountains: 1) receive among the highest rates of atmospheric deposition measured in North America, 2) contain old-growth forests, 3) have shown declines in forest health, 4) have sustained high insect-caused fir mortality, and 5) contain poorly buffered soils and stream systems. High rates of nitrogen and sulphur deposition (similar to 1900 and similar to 2200 Eq . ha(-1)yr(-1), respectively) are dominated by dry and cloud deposition processes. Large leaching fluxes of nitrate-nitrogen (100-1400 Eq . ha(-1)yr(-1)) occur within the soil profile. We have expanded the study to the watershed scale with monitoring of: precipitation, throughfall, stream hydrology,and stream chemistry. Two streamlets drain the 17.4 ha Noland Divide Watershed (1676-1920m) located in the Great Smoky Mountains National Park. A network of 50 20x20 m plots is being used to assess stand structure, biomass, and soil nutrient pools. Nitrate is the predominant anion in the streamlets (weighted concentrations: 47 and 54 mu eq . L(-1) NO3-; 31 and 43 mu eq . L(-1) SO42-). Watershed nitrate export is extremely high (similar to 1000 Eq . ha(-1) yr(-1)), facilitating significant base cation exports. Stream acid neutralizing capacity values are extremely low (-10 to 20 mu eq . L(-1)) and episodic acidifications (pH declines of a full unit in days or weeks time) occur. Annual streamwater sulfate export is on the order of 770 Eq . ha(-1)yr(-1) or about one-third of total annual inputs, indicating there is net watershed sulfate retention. The system is highly nitrogen saturated (Stage 2, Stoddard, 1994) and this condition promotes both chronic and episodic stream acidification.