Atmospheric deposition of reactive nitrogen to a deciduous forest in the southern Appalachian Mountains

Abstract. Assessing nutrient critical load exceedances requires complete and accurate atmospheric deposition budgets for reactive nitrogen (Nr). The exceedance is the total amount of Nr deposited to ecosystem in excess load, which input below harmful effects do not occur. Total includes all forms (i.e., organic inorganic) by wet dry pathways. Here we present results from Southern Appalachian Nitrogen Deposition Study (SANDS), a combination measurements field-scale modeling was used develop annual budget deciduous forest at Coweeta Hydrologic Laboratory. Wet ammonium, nitrate, nitrite, bulk N were measured directly. fraction estimated using bidirectional resistance-based model driven with speciated air concentrations (e.g., ammonia, ammonium aerosol, nitric acid, nitrate alkyl nitrates, peroxy nitrates), micrometeorology, canopy structure, biogeochemistry. ∼ 6.7 kg ha−1 yr−1, on upper end estimates recently developed similar ecosystems nearby Great Smoky Mountains National Park. Of (wet + dry) budget, 51.1 % contributed reduced (NHx = ammonia ammonium), oxidized contributing 41.3 7.6 %, respectively. Our indicate that reductions NHx would be needed achieve lowest (∼ 3.0 yr−1) loads southern forests.