HR: 11:11h
AN: H52C-04    [Abstracts]
TI: Hydrochemical Response to Drought Conditions at an Alpine Watershed, Colorado Front Range
AU: * Hill, K R
EM: kenneth.hill@colorado.edu
AF: University of Colorado Institute of Arctic and Alpine Reserach, 1560 30th St. Campus Box 450, Boulder, CO 80303, United States
AU: Williams, M W
EM: markw@culter.colorado.edu
AF: University of Colorado Institute of Arctic and Alpine Reserach, 1560 30th St. Campus Box 450, Boulder, CO 80303, United States
AU: Caine, N
EM: cainen@colorado.edu
AF: University of Colorado Institute of Arctic and Alpine Reserach, 1560 30th St. Campus Box 450, Boulder, CO 80303, United States
AU: Janke, J R
EM: jjanke1@mscd.edu
AF: Metropolitan State College of Denver, Department of Earth and Atmospheric Sciences Campus Box 22, Denver, CO 80217, United States
AU: Hartman, M D
EM: melannie@nrel.colostate.edu
AF: Colorado State University Natural Resource Ecology Laboratory, Campus Delivery 1499, Fort Collins, CO 80523, United States
AB: Extreme climate events play a key role in alpine hydrochemistry by altering source waters and flowpaths. Persistent drought conditions from 2000-2002 at Green Lakes Valley resulted in precipitation and streamflow about 75% of normal for the last 25 years. Surprisingly, both concentrations and fluxes of geochemical weathering products and nutrients increased during the drought at the higher elevation sites. Niwot Ridge LTER has continuously monitored streamflow, precipitation chemistry, and water quality for 25 years in Green Lakes Valley at 8 sites representing an elevation gradient extending from 3250 meters at the valley outlet to 4000 meters at the continental divide. Comparing continuous 5-year blocks of above-average precipitation (1993-1997) vs. below-average years (2000- 2004), both concentrations and fluxes were significantly higher during drought for base cations (p<0.05) throughout upper Green Lakes Valley. DAYCENT modeled predicted discharge correctly during the period of above-average precipitation but underpredicted discharge during drought conditions, suggesting an additional source of water. End Member Mixing Analyses (EMMA) conducted during 1996 constrains streamflow as a mixture of snowmelt, talus water, and groundwater with subsurface flowpaths contributing more than 50% of streamflow, even during snowmelt (Liu, 2004). However, EMMA results during drought years using chemical and isotopic compositions from surface water, talus springs, snowpits, snowmelt, soil water, and groundwater suggest an additional, unidentified source of streamflow. One possible end member is melting permafrost within the basin. We downscaled a qualitative, regional permafrost distribution model of the Colorado Front Range to investigate the potential role of melting permafrost on hydrochemical characteristics in Green Lakes Valley. Model results indicate that increasing mean annual air temperature by 1 degree Celsius results could melt 35% of permafrost in the watershed. Future monitoring and research efforts will examine the potential irreversible effects of extreme climate events and permafrost melt on alpine ecosystems.
DE: 1830 Groundwater/surface water interaction
DE: 1871 Surface water quality
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting