The Effect of Nitrogen Depostition and Edaphic Conditions on Microbial Activity in the Alpine Zone of the Grand Teton National Park

Abstract

Atmospheric nitrogen (N) deposition rates show increasing N loadings since the 1980s in the western U.S. associated with increasing N emissions from industrial, urban, and agricultural sources (Fenn et al., 2003). Compared to the eastern U.S., the number of NADP/NTN (National Atmospheric Deposition Program/ National Trends Network) and CASTNet (Clean Air Status Network) monitoring sites is much more limited in the west, and they are rarely located in the highest-elevations, where ecosystems are likely to be more sensitive (Bums 2004). Although N deposition tends to increase with elevation in this region (Williams and Tonnesen 2000), there are considerable uncertainties about the actual N deposition levels in the Rocky Mountains. Model-simulations indicate a "hotspot" of N deposition near Grand Teton National Park (GRTE) (Fenn et al., 2003; Nanus et al. 2003), with feedlot and fertilizer N emissions in Southern Idaho, as potential sources impacting the alpine communities in GRTE. However, little data is currently available on the actual atmospheric N inputs to alpine ecosystems in GRTE, either as snow during winter or wet and dry deposition during the short snow-free period.