Hotspots of Nitrogen Cycling Activity in an Alpine-Subalpine Watershed on Niwot Ridge

Anthony Darrouzet-Nardi
University of Colorado at Boulder
Department of Ecology and Evolutionary Biology


Within a watershed, certain areas or components of it are likely to be hotspots of biogeochemical activity. This project was designed to locate nitrogen cycling hotspots within a heterogeneous alpine-subalpine watershed at the Niwot Ridge LTER site in the Front Range of the Rocky Mountains, Colorado. I used spatially explicit sampling methods to characterize soil moisture, soil temperature, pH, the nitrogen and carbon concentrations and stable isotope ratios in light and heavy soil fractions, nitrification rates, mineralization rates, and availability of inorganic nitrogen. Nitrogen concentration and isotope data suggest that within the forested areas, where plant diversity is limited to several trees, there are clear associations of nitrogen cycling activity with physical conditions such as temperature and moisture. However, within the open tundra and subalpine meadows, there is more heterogeneity, which may be associated with higher species diversity. There are also anomalous isotope values associated with the swampy areas that form at the sideslope-toeslope transition, suggesting that these are areas of interest for ecosystem processing of nitrogen.