Critical Loads Of Sulfur And Nitrogen And Modeled Effects Of Deposition Reduction For Forested Ecosystems Of Great Smoky Mountainins National Park PDF Download

A critical load (CL) is a science-based threshold that identifies the amount of pollutant deposition below which no significant ecological harm to an ecosystem component is expected. This report provides baseline critical load (CL) analyses for nitrogen (N) and sulfur (S) as required under the 2012 Planning Rule for forest plan assessments. The data also can be used to inform land management decisions where the effects of N and S deposition are relevant, including the evaluation of large projects through the National Environmental Policy Act, Prevention of Significant Deterioration (PSD) permitting program, wilderness monitoring, and watershed condition. Significant portions of the USDA Forest Service system lands in the Intermountain Region are exposed to N deposition levels that exceed CLs. Areas in exceedance have an increased risk of negative ecological effects. Nine of the 12 National Forests within the Intermountain Region have areas that exceed CLs for surface water acidification and therefore are at higher risk for declines in abundance and diversity of aquatic species. All 12 National Forests have areas that exceed CLs for surface water eutrophication, lichen species richness, forage lichen abundance, and tree species growth rate and probability of survival (over 10 years). In areas with increased risk of surface water eutrophication, competitive interactions and community structure of primary producers can shift and cause compounding effects within the food web. Diversity and abundance of key aquatic species may decrease to the point of extirpation. Areas that exceed CLs for lichen species richness and forage lichen abundance have an increased risk to experience reduced diversity, occurrence, and abundance of lichen species which can negatively affect other biota such as mammals, birds, and invertebrates, that rely on lichens for food, shelter, and camouflage. Areas with an increased risk for declines in tree growth rate and probability of survival may experience a change in the composition of forest communities.