BIOGEOMON Journal of Conference Abstracts, Vol 2(2), p. 143, 1997
Mindia Brown
Mark W. Williams
Nel Caine
Isotopic separation was significant among potential water
sources, based on delta o18 ratios of -19.8 (sd = 1.1)
for the snowpack, -12.3 (sd 2.4) for rainfall, and
from -16.1 to -12.5 in interstitial waters.
Average delta o18 values for stream waters decreased from
-19.2 at the head of the Green Lakes Valley to -15.7
at a low elevation sampling site in the Green Lakes Valley;
analytical precision of all samples was +-0.1 delta o18.
Our preliminary analysis using a two-component mixing model
indicates that at any time the percentage of antecedent water
in streamflow increases with the area of the catchment.
For example, on 21 June, 1990, the delta o18
of streamflow in headwater basins
was indistinguishable from that of meltwater,
indicating that less than 1% of streamflow
was from antecedent water in catchments of about 8 ha.
The precentage of antecedent water in streamflow
increased to 23% with a basin area of 42 ha (Navajo site),
to 50% with a basin area of 135 ha (Green Lakes 5),
to 57% with a basin area of 221 ha (Green Lakes 4),
and to 77% with a basin area of 355 ha (inlet to Lake Albion).
A three-component mixing model was used
to partition streamflow into:
i) meltwater that becomes overland flow;
ii) meltwater that infiltrates surficial deposits and
is then discharged back to streamflow as interflow
or saturated return flow; and
iii) antecedent water stored in vadose and groundwater
reservoirs prior to snowmelt. The partitioning was conducted
using Si and delta o18 values as independent tracers.
As in the two-component model, delta o18 values were used
to discriminate meltwater versus antecedent water.
The Si values are used to discriminate meltwater that has
infiltrated surficial deposits versus classic Hortonian
overland flow. Application of the three-component model to
headwater basins shows that subsurface flow contributed
about 50% of streamflow during snowmelt. This subsurface
component is composed primarily of snowmelt that infiltrates
surficial deposits and is then discharged as return flow
where the rising water table intersects the ground surface.
Antecedent water contributed relatively little
to streamflow. The remaining portion of stream flow is
primarily from water traveling laterally through the snowpack
to channels or across the snow-soil interface to channels.
INSTAAR and Department of Geography
University of Colorado
Boulder, CO
INSTAAR and Department of Geography
University of Colorado
Boulder, CO
INSTAAR and Department of Geography
University of Colorado
Boulder, CO
Abstract:
We are conducting a study in in the Green Lakes Valley of the
Colorado Front Range to understand the processes that determine
the sources and flowpaths of solutes in high-elevation catchments.
Hydrologic pathways were evaluated in 1990 using a sampling protocol
that included the quantity and quality of atmospheric deposition,
the snowpack, snowpack meltwaters, soil interstitial water,
groundwater, and stream waters.
Approximately 400 samples were analyzed for their isotopic
ratios of H/D and o18/o16,
and for concentrations of reactive silicate (Si) and major ions.
Our sampling protocol permits evaluation of the sources,
residence time and pathways of streamflow
in this system throughout the year
and at scales that vary from 8 ha to 10 km2.