Hydrologic Processes, V 11, N 13, 1997 (in press).
Mark W. Williams
Thomas Davinroy
Paul Brooks
INSTAAR and Department of Geography
University of Colorado
Boulder, CO
INSTAAR and Department of Geography
University of Colorado
Boulder, CO
US Geological Survey
Boulder, CO
Abstract:
Organic and inorganic pools of nitrogen (N) were
measured in talus fines or "soils" and subtalus water
during the summer of 1995 in the alpine
Green Lakes Valley catchment of the Colorado Front
Range.
Nineteen talus samples were divided into four classes:
subtalus dry, subtalus wet,
surface vegetated and surface bare.
The size of individual talus soil patches
ranged from 0.5 to 12.0\|@m2@ in area,
with bulk density ranging from 0.98 to 1.71\|@kgm3@ and
soil texture ranging from sandy gravel in the subsurface talus
to a loam in the vegetated surface.
All samples contained KCl-extractable
@nh4@ and @no3@,
organic N and carbon (C),
and 17 of 19 samples contained microbial biomass.
The mean subtalus values for KCl-extractable @nh4@ of 3.2\|@mgNkg@ and
@no3@ of 1.0\|@mgNkg@ were comparable to developed alpine soils
on Niwot Ridge.
Average subtalus microbial biomass of 5.4\|@mgNkg@ and
total N of 1,000\|@mgNkg@ were about an order of magnitude
lower than alpine tundra soils,
reflecting the reduced amount of vegetation in talus areas.
However, these measurements in surface vegetated patches
of talus were comparable to the well-developed soils on Niwot Ridge.
These measurements in talus of microbial biomass,
total N, and KCl-extractable @nh4@ and @no3@,
show that there is a viable organic system in talus.
Mean @no3@ concentrations of 20\|@mueq@ from 29 samples of subtalus
water were significantly higher than the 6.7\|@mueq@ in snow,
while @nh4@ concentrations in subtalus water of 0.7\|@mueq@
was significantly lower than in snow at 5.2\|@mueq@ (@p@\|=\|0.001).
Nitrate concentrations in subtalus water were significantly (@p@\|<\|0.0001)
correlated with concentrations of geochemical weathering products
such as @ca@ (@r2@\|=\|0.84) and silica (@r2@\|=\|0.49).
The correlation of @no3@ in subtalus water with
geochemical weathering products
suggests that @no3@ concentrations in subtalus water increase
with increased residence time,
consistent with a biological source for this subtalus water @no3@.
The high @no3@ concentrations in subtalus water compared
to atmospheric deposition of @no3@ indicates that @no3@ in
talus is mobile and may contribute to @no3@ in stream waters
of high-elevation catchments.