HR: 0800h
AN: C41A-0048    [Abstracts]
TI: Stream Flow Contributions of Rock Glaciers in the Southern Sierra Nevada Mountains of California
AU: * Kirchner, P
EM: pkirchner@ucmerced.edu
AF: Sierra Nevada Research Institute, University of California, Merced, P.O. Box 2039, Merced, Ca 95344,
AU: Rice, R
EM: rrice@ucmerced.edu
AF: Sierra Nevada Research Institute, University of California, Merced, P.O. Box 2039, Merced, Ca 95344,
AU: Liu, F
EM: fliu@ucmerced.edu
AF: Sierra Nevada Research Institute, University of California, Merced, P.O. Box 2039, Merced, Ca 95344,
AB: Rock glaciers are an important contributor to base flow and a source of nitrate in high mountain environments but we presently have little understanding of the magnitude of this contribution or their biogeochemical behavior. In this study we investigate 2 ice-cored rock glaciers located in the Southern Sierra Nevada and determine the contribution they provide to surface flow in their respective watersheds. Water samples were collected at the outlet and downstream of the rock glaciers in the summer and fall of 2006 and 2007 and stream flow was monitored continuously at the outlet of the rock glacier from July 2006-2007. Water samples were analyzed for stable isotopes ( δ ¹⁸O and δ) and major ions. Results show a distinct shift from snow to subsurface dominated flows occurred seasonally from July to October in 2006 and also intra-annually from 2006 to 2007 as δ D increased from -125‰l to -110‰l, when the subsurface flows originated from the melting ice-core of the rock glacier. This earlier shift to subsurface dominated stream flow corresponded with a lower than normal snow pack. Using the stable isotope ( δ D) and conductivity, a two- component hydrograph mixing model provided further details indicating that snow melt accounted for >60% of the stream flow, but declined to <40% in October 2006 and July 2007. Nitrate concentrations generally increased seasonally from 5.3 μ eq L^-1 to 20.5 μ eq L^-1 suggesting the existence of unique microbial communities within rock glaciers. However, these nitrate values are significantly lower than results from the Rocky Mountains where atmospheric contributions to nitrate formation are higher.
DE: 0469 Nitrogen cycling
DE: 0720 Glaciers
DE: 0722 Rock glaciers
DE: 1800 HYDROLOGY
SC: Cryosphere [C]
MN: 2007 Fall Meeting