HR: 08:45h
AN: B11E-04    [Abstracts]
TI: CO2 and Carbon Isotopes of CO2 Within a Subalpine Forest Snowpack
AU: * Bowling, D R
EM: bowling@biology.utah.edu
AF: Dept. of Biology, University of Utah, Salt Lake City, UT 84112-0820, United States
AU: Schaeffer, S M
EM: schaeffer@biology.utah.edu
AF: Dept. of Biology, University of Utah, Salt Lake City, UT 84112-0820, United States
AU: Massman, W J
EM: wmassman@fs.fed.us
AF: U.S.D.A. Forest Service, 240 West Prospect, Fort Collins, CO 80526, United States
AU: Monson, R K
EM: Monsonr@Colorado.edu
AF: Dept of Ecology and Evolutionary Biology, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Williams, M W
EM: markw@snobear.colorado.edu
AF: Dept of Geography, and Institute for Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, United States
AB: Stable isotopes are useful to examine a variety of carbon cycle processes, and have been used to link the carbon isotope ratio (δ¹³C) of CO₂ in soil respiration to weather events in summer. Recent studies have shown that many high-elevation and high-latitude ecosystems can lose a significant amount of carbon in the winter by respiration under the snowpack. Very little is known about the carbon isotope content of winter respiration in seasonally snow-covered forests. During winter and spring 2006-2007, CO₂ was monitored within a snowpack at the Niwot Ridge AmeriFlux site in the Rocky Mountains of Colorado (3050 m elevation). CO₂ and δ¹³C of CO₂ were monitored in vertical profiles within the forest, within the snowpack, at the soil-snow interface, and within the soil, using tunable diode laser spectroscopy. Ancillary measurements included wind and other weather measurements, snow and soil temperature, soil moisture, and snowpack hydrology (density profiles, snow water equivalence or SWE). During the study period, SWE increased from 30 to 50 cm, and then decreased until the snow was fully melted. Snow depth peaked at 140 cm. Soil temperatures in the top few cm of soil ranged from -1 to 0 C, and within the snowpack from -15 to 0 C. Measured CO₂ at the soil-snow interface ranged from 1500 to 3500 ppm, and peaked when SWE was maximum in late April. δ¹³C at the soil-snow interface ranged from – 8 to -21 permil. Within the snowpack, CO₂ ranged from 400 to 3000 ppm, and δ¹³C ranged from -8 to -20 permil. Gradients in both CO₂ and δ¹³C were dependent on wind conditions above the snowpack. Mixing lines between δ¹³C and CO₂ were confined to a relatively narrow range, with an inferred isotope ratio of respiration of -27.1 permil (assuming a 4.4 permil kinetic fractionation). These data will be discussed in the context of expected δ¹³C of respiration based on measurements in air.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1851 Plant ecology (0476)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting