Assessing the Nitrogen Saturation Status of Appalachian Forests using Stable Isotopes of Nitrate

Chronic elevated nitrogen (N) deposition can lead to ecosystem N saturation, which is theorized to occur when N supply exceeds biological demand and excess N leaches to receiving waters. This research examined the post-depositional fate and transport of atmospheric nitrate in Appalachian forests across spatial and temporal scales by characterizing the nitrate stable isotopic composition (δ15N, δ18O, and Δ17O) of precipitation, soil water, and streams. Data indicate that elevated N deposition does not saturate biological demand; rather, N processing becomes more extensive as N availability increases. Along a regional N deposition gradient (North Carolina to New Hampshire), mean proportions of atmospheric nitrate in streams were inversely related to long-term annual average nitrate deposition. Stream nitrate concentrations were also negatively correlated to the proportion of atmospheric nitrate in streams (R2=0.23; p