Meixner, T W Bales, R C
Mark W Williams
Campbell, D H
Baron, J S
Department of Hydrology and Water Resources
University of Arizona Tucson, AZ 85721-0011 United States
Department of Hydrology and Water Resources
University of Arizona Tucson, AZ 85721-0011 United States
Department of Geography and
Institute of Arctic and Alpine Research
University of Colorado, Boulder
USGS-WRD, Federal Center
USGS-BRD
NREL
Colorado State University, Fort Collins, CO 80523
Abstract
We evaluated the sensitivity of water quality
to flow routing in two high-elevation Rocky Mountain
catchments, the Andrews Creek subcatchment
(part of the Loch Vale watershed, Rocky Mountain National Park)
and the Green Lakes watershed (part of the
Niwot Ridge LTER), with quite different relative flow paths
through soil and talus. Both sites had comparable
data sets from 1994 and 1996, including high-resolution
spatial data and high frequency time series of hydrology, geochemistry
and meteorology.
We used the Alpine Hydrochemical Model (AHM) to
evaluate the relative importance of
soil and talus geochemical processes on stream chemical composition.
The model of each watershed consisted of three
terrestrial subunits; soil, talus and rock with the routing
between the subunits determined by spatial land cover data.
For both watersheds 1994 data were used for model
calibration and 1996 data for evaluation.
In Andrews Creek where all snowmelt, including that on soil, flows through
talus enroute to the stream, stream composition was only sensitive
to parameters describing chemical reactions in talus.
The opposite was true for
Green Lakes, where all snowmelt contacts soil enroute
to the stream. Field measurements at
both watersheds indicate that talus pore waters exert a
significant control on stream chemistry. The contradiction
of modeling results with field measurements suggests
that it will be necessary to quantify the hydrologic
and chemical properties of landcover classes (e.g. soil and talus)
in order to understand flow routing within a watershed.