Nitrogen Dynamics in Paired High Elevation Catchments
during Spring Snowmelt 1996, Rocky Mountains, Colorado
Kristi Heuer1, Paul D. Brooks2, and Kathy A. Tonnessen1
Alteration of the nitrogen (N) cycle is a concern in high elevation ecosystems of the western United
States due to the potential adverse effects of atmospheric N deposition on aquatic and terrestrial
resources. Surface waters in the Rocky Mountains are especially sensitive to small changes in N
deposition, most of which is deposited in seasonal snowpacks. Isotopic analyses have shown that the
majority of N in the snowpack enters soil inorganic N pools during spring snowmelt before being
transported to the stream. It has been suggested that the export of N in streamwater is regulated by
microbial transformations of N throughout the winter in thawed soils beneath the snowpack. The
objective of this study is to evaluate the spatial and temporal variability in N sources, sinks, and
streamwater N export during spring snowmelt in two high elevation catchments. Snowpack, soil,
soil leachate, and streamwater samples were analyzed for inorganic N in Snake River and Deer
Creek catchments during snowmelt 1996. Both catchments are located in Summit County, Colorado,
and range in elevation from 3350 to 4120 m.
Soil pools and atmospheric inputs from a melting snowpack are two possible contributors to N in
streamwater during the initial phase of spring snowmelt. Soil N pools in Deer Creek and Snake
River, 1868 and 1252 mg N m2, respectively, were two orders of magnitude greater than N inputs
from snow, 88 mg N m2, indicating that soil N is a potentially larger source of N in surface water.
Consequently, small changes in the fate of this pool may have a much larger impact on N export than
changes in N inputs from snow. The potential for soils to be N sources during spring snowmelt was
evaluated by the leaching of nitrate ( NO3 ). Nitrate leachate from Deer Creek alpine soils, 684 mg N
m2, was significantly greater than from forest and meadow soils (p < 0.001). Leachate from Deer
Creek forest soils was calculated at 44 mg N m2, indicating net N immobilization. This pattern of
NO3 leachate from soils was consistent with patterns of streamwater NO3 concentrations along an
elevational gradient. Concentrations in the alpine were highest, 0.22 mg N L1, and decreased to
0.13 mg N L1 further downstream.
Patterns in streamwater N in both catchments were consistent with patterns in soil leachate, indicat-
ing that soil processes, in addition to hydrological processes, are important in controlling N export
from these high elevation catchments. Soils function as both sources and sinks of N during spring
snowmelt; alpine soils were a significant source of N to the stream, while forest soils were N sinks.
Greatest variability in soil processes occurs in the alpine of these catchments, which until recently
were also the least studied. To better understand N dynamics in these high elevation catchments,
further research should be directed towards understanding variable soil processes in the alpine and
their effects on N source/sink relationships during the snow-covered season.
National Park ServiceAir Resources Division, P.O. Box 25287, Denver, Colorado 80225-0287, USA
U.S. Geological SurveyWater Resources Division, 3215 Marine Street, Boulder, Colorado 80303, USA