HR: 0800h
AN: C21B-0445    [Abstracts]
TI: Subniveal Carbon Flux in a Wyoming Subalpine Ecosystem
AU: * Cable, J M
EM: jcable1@uwyo.edu
AF: University of Wyoming Department of Botany, 1000 E. University Ave., Laramie, WY 82071, United States
AU: Ogle, K
EM: kogle@uwyo.edu
AF: University of Wyoming Department of Botany, 1000 E. University Ave., Laramie, WY 82071, United States
AU: Ogle, K
EM: kogle@uwyo.edu
AF: University of Wyoming Department of Statistics, 1000 E. University Ave., Laramie, WY 82071, United States
AU: Williams, D G
EM: dgw@uwyo.edu
AF: University of Wyoming Department of Renewable Resources, 1000 E. University Ave., Laramie, WY 82071, United States
AB: Winter soil biological activity may significantly impact annual carbon balance and post-winter processes in subalpine ecosystems. Soil microbial communities are generally active in the subniveal environment due to insulation from the snowpack, allowing winter soil temperatures to remain above freezing. Snowpack characteristics such as snow density and temperature can vary over a season, potentially impacting subniveal processes such as soil respiration because of altered insulation properties. Little is known about the magnitude and variation in subniveal soil CO₂ production (due to root and microbial respiration) in subalpine ecosystems. We estimated subniveal CO₂ production over a winter season with variable snowpack conditions by sampling forested and open meadow areas in a subalpine ecosystem in the Snowy Range of Wyoming in February (winter) and April (spring). We measured CO₂ concentration, oxygen (¹⁸O) and carbon (¹³C) isotope ratios of CO₂, snow density, and snow temperature at multiple positions within the snow profile. These data were integrated with a dynamic CO₂ diffusion model that incorporates the effects of snow pack properties on CO₂ diffusion. The data and model were coupled to (1) partition the contribution of subniveal vs. atmospheric sources or CO₂ to total CO₂ efflux at the snow surface and (2) estimate subniveal (i.e., soil-derived, biological) CO₂ production rates. We evaluated whether the ¹⁸O signature of snow and soil water could trace the biological CO₂ source. Within the meadow sites, respiration rates were similar between the winter and spring periods. Within the forested sites, soil respiration was higher in the spring compared to the winter. Differences in soil respiration could be due to (1) differences in subniveal CO₂ production rates, (2) differences in CO₂ diffusion created by changing snowpack conditions, and/or (3) changes in the diffusion or "pumping" of atmospheric CO₂ into the snow profile. Yet, the ¹³C signal was more depleted in the spring, suggesting that spring subniveal CO₂ production may be more affected by root respiration and/or microbial substrate use may change. The dual isotope approach (¹⁸O and ¹³C in CO₂) was useful for determining source contribution in the winter but less so in the spring because freeze-thaw dynamics of spring snowpack may cause significant exchange of ¹⁸O between CO₂ and H₂O in the snow profile. Since little/no primary productivity occurs during the winter, subniveal soil activity could greatly affect the annual carbon balance of such systems by increasing soil carbon loss, but the degree to which it controls annual, net ecosystem exchange is largely determined by variation in snow properties. Integrating the biological and physical components of winter-driven systems may be critical in determining how changes in winter climate will impact these ecosystems at larger spatial and temporal scales.
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0736 Snow (1827, 1863)
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Cryosphere [C]
MN: 2007 Fall Meeting