HR: 0830h
AN: H41D-1031    [PDF]
TI: Rock glaciers as a source of nitrate to alpine streams, Green Lakes Valley, Colorado, USA.
AU: * Knauf, M
EM: knauf@colorado.edu
AF: University of Colorado, Department of Geography, 260 UCB, Boulder, Co 80309 United States
AU: * Knauf, M
EM: knauf@colorado.edu
AF: INSTAAR, 1560 30th Street, Boulder, Co 80309 United States
AU: Williams, M W
EM: markw@snobear.colorado.edu
AF: University of Colorado, Department of Geography, 260 UCB, Boulder, Co 80309 United States
AU: Williams, M W
EM: markw@snobear.colorado.edu
AF: INSTAAR, 1560 30th Street, Boulder, Co 80309 United States
AU: Caine, N
EM: cainen@colorado.edu
AF: University of Colorado, Department of Geography, 260 UCB, Boulder, Co 80309 United States
AU: Caine, N
EM: cainen@colorado.edu
AF: INSTAAR, 1560 30th Street, Boulder, Co 80309 United States
AB: An ongoing concern in alpine areas of the western United States is the high concentrations of nitrate in surface waters. A number of research scientists have shown that talus areas are one source of this elevated nitrate (Williams et al., 1997; Campbell et al., 2002). Here we evaluate the potential contribution of nitrate to surface waters from a previously overlooked source: rock glaciers. Water draining from the Green Lake 5 rock glacier in the Colorado Front Range has been sampled for nitrate and ammonium since 1998 as part of the Niwot Ridge LTER program. The mean concentration of nitrate in stream waters in the Green Lakes Valley is 16.12 ueq/L, and for talus streams is 20 ueq/L. In comparison, the stream draining the rock glacier has an average nitrate concentration of 54 ueq/L. Moreover, nitrate values from the stream draining the rock glacier peak in the late summer at over 100 ueq/L. The sources of these high nitrate values from the rock glacier are unknown at this time; we evaluate several hypotheses. Increased nitrate could be a result of dry deposition on the rock glacier that is flushed during snowmelt and rain events. Another hypothesis is that microbial processes within the rock glacier have contribute to higher nitrate concentrations. Here we evaluate the sources and fate of nitrate in waters draining the Green Lake 5 rock glacier in 2003 using a combination of stable (delta O18) and radiogenic (tritium) water isotopes, fractionation of dissolved organic matter, fluorescence index of dissolved organic matter, and mineralization experiments. These site-specific results are then placed in a regional context through a synoptic sampling of streams draining rock glaciers throughout the Rocky Mountain region. Works Cited Williams, M. W., T. Davinroy, and P. D. Brooks. 1997. Organic and inorganic nitrogen pools in talus soils and water, Green Lakes Valley, Colorado Front Range, Hydrologic Processes, 11(13): 1747-1760. Campbell, Donald H., Carol Kendall, Cecily C. Y Chang, Steven R. Silva, and Kathy A. Tonnessen. 2002. Pathways for nitrate release from an alpine watershed: Determination using delta N15 and delta O18. Water Resources Research. 11 May. Doi: 10.1029/2001WR000294.
DE: 1030 Geochemical cycles (0330)
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting