HR: 1340h
AN: B23A-0919    [Abstracts]
TI: Comparison of Soil CO2 Concentrations and Surface CO2 Efflux Across Riparian-Hillslope Transitions: Wet Versus Dry Growing Seasons
AU: * Pacific, V J
EM: vincent.pacific@myportal.montana.edu
AF: Montana State University, 334 Leon Johnson Hall P.O. BOX 173120, Bozeman, MT 59715, United States
AU: McGlynn, B L
EM: bmcglynn@montana.edu
AF: Montana State University, 334 Leon Johnson Hall P.O. BOX 173120, Bozeman, MT 59715, United States
AU: Riveros-Iregui, D
EM: diego.riverosiregui@myportal.montana.edu
AF: Montana State University, 334 Leon Johnson Hall P.O. BOX 173120, Bozeman, MT 59715, United States
AU: Welsch, D
EM: dwelsch@frostburg.edu
AF: Frostburg State University, Department of Geography Frostburg State University, Frostburg, MD 21532, United States
AU: Epstein, H
EM: hee2b@virginia.edu
AF: University of Virginia, P.O. BOX 400123, Charlottesville, VA 22904, United States
AB: An outstanding gap in our understanding of carbon cycling is the role of climate variability on soil CO₂ production and surface CO₂ efflux. Few studies have contrasted soil respiration across wet and dry growing seasons. Inter-annual climate variability, specifically earlier snowmelt and decreased growing season precipitation, can impact soil water content and soil temperature, which partially control soil respiration. We investigated the spatial and temporal variability of soil CO₂ concentrations and surface CO₂ efflux across 4 topographically distinct riparian-hillslope transitions with strong gradients in water content and temperature. Our study sites were located in the 380 ha subalpine upper-Stringer Creek Watershed in the Tenderfoot Creek Experimental Forest, Montana. We present data from wet (2005) and dry (2006) growing seasons: June-August. Precipitation was 27 versus 16.5 cm and peak snowmelt occurred on June 6 and April 20, respectively. We collected measurements of soil temperature, soil water content, soil air CO₂ concentrations (20 cm and 50 cm), and surface CO₂ efflux at 32 locations across four transects and highlight results from one characteristic transect. Comparing wet:dry growing seasons, all locations had similar maximum soil water content, but the range was greater (minimum was lower) during the drier growing season. Median hillslope soil water content (17:10 %), and median soil CO₂ concentrations at 20 cm (2200:1800 ppm) and surface CO₂ efflux (0.48:0.43 g CO₂ m^-2 hr^-1) were all lower during the dry growing season. In riparian zones, median soil water content was much lower in the dry growing season (52:43 %). However, median riparian soil CO₂ concentrations (10,200:15,400 ppm) and surface CO₂ efflux (0.48:0.61 g CO₂ m^-2 hr^-1) were much higher during the dry growing season. In addition to differences in magnitude of CO₂ and environmental variables, the timing of peak riparian soil CO₂ concentrations and surface CO₂ efflux shifted 12 and 6 weeks earlier from the wet to the dry growing season. Conversely, hillslope soil CO₂ concentrations and surface CO₂ efflux timing was consistent across both seasons. Our results suggest that inter-annual climate variability, specifically earlier snowmelt and decreased growing season precipitation, can impact growing season soil water content and temperature, leading to increased/decreased flux magnitudes and shifts in peak fluxes of weeks to months.
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting