Sickman, J. O. Institute for Computational Earth System Science, University of California, Santa Barbara, sickman@icess.ucsb.edu
Chang, C. O. United States Geological Survey, ccchang@usgs.gov
Kendall, C. United States Geological Survey, ckendall@usgs.gov
Melack, J. M.. Institute for Computational Earth System Science, University of California, Santa Barbara, Melack@lifesci.ucsb.edu

 
DETERMINATION OF NITRATE SOURCES IN CATCHMENTS DURING SNOWMELT USING OXYGEN AND NITROGEN ISOTOPES OF NITRATE; SIERRA NEVADA, CALIFORNIA
 
Using a recently developed technique for collection and determination of oxygen and nitrogen isotopes of nitrate in dilute waters, we evaluated the relative contribution of atmospheric nitrate and catchment-derived nitrate in high-elevation catchments of the Sierra Nevada. The study sites included the Emerald Lake (ELW), Topaz Lake (TLW) and High Lake (HLW) watersheds, and the Marble Fork of the Kaweah River (MFK). Nitrate isotopes were measured in samples from the seasonal snowpack (atmospheric nitrate), in streams during winter baseflow (catchment-derived nitrate) and during snowmelt runoff. Snowpack nitrate (delta 15N = +3.6 to +6.1 per mil, delta 18O = +24.0 to +35.1 per mil) was isotopically distinct from catchment-derived nitrate (delta 15N = -5.2 per mil, delta 18O = +10.5 to +15.4 per mil). Nitrate isotopes in samples from ELW, MFK and HLW were very similar in composition to catchment-derived values: delta 15N = -1.9 to -4.2 per mil, delta 18O = +10.6 to +23.3 per mil. At TLW the oxygen isotope was heavier (18O = +22.7 to +33.4 per mil) and more similar to atmospheric nitrate. We conclude that most nitrate found in high elevation streams during snowmelt in the Sierra Nevada is derived from catchment sources.
 
Day: Wednesday, Feb. 3
Time: 08:45 - 09:00am
Location: Eldorado Hotel
 
Code: SS32WE0845E