Campbell, D. H. US Geological Survey, dhcampbe@usgs.gov
Kendall, C. H. US Geological Survey, ckendall@usgs.gov
Tonnessen, K. A. National Park Service, Kathy_Tonnessen@nps.gov
Chang, C. C. US Geological Survey, ccchang@usgs.gov
Silva, S. R. US Geological Survey, srsilva@usgs.gov

 
BIOGEOCHEMICAL PROCESSES CONTROLLING NITROGEN RELEASE FROM ALPINE ECOSYSTEMS: DETERMINATION USING ISOTOPES OF NITRATE
 
The isotopes d15N and d18O of nitrate were analyzed in snowpack samples from many locations in the Rocky Mountains, and in melt water, precipitation, surface water, and ground water samples from the Loch Vale watershed in Colorado to determine processes controlling the release of nitrogen from alpine and subalpine ecosystems. Although substantial overlap was found between the d15N values for all water types (-4 to +6 permil), most d18O values for surface- and ground-water (+10 to +30 permil) were distinct from snowpack, melt water, and precipitation values (+40 to +70 permil). Samples collected during the earliest part of the snowmelt period indicated that a large proportion of the nitrate in suface- and ground-water came directly from atmospheric deposition. However, throughout most of the spring and summer, d18O values in surface- and ground-water were lighter, indicating a substantial contribution of nitrate from microbial nitrification. Among the snowpack and precipitation samples, geographic and seasonal patterns were evident in the d15N values, suggesting potential for identification of nitrogen-emission source categories that contribute to atmospheric deposition.
 
Day: Wednesday, Feb. 3
Time: 11:45 - 12:00pm
Location: Sweeney Center
 
Code: SS50WE1145S