HR: 1340h
AN: B23A-0917    [Abstracts]
TI: Diurnal Hysteresis Between Soil CO2 and Soil Temperature is Controlled by Soil Water Content
AU: * McGlynn, B L
EM: bmcglynn@montana.edu
AF: Dept. Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: Riveros-Iregui, D A
EM: diego.riverosiregui@myportal.montana.edu
AF: Dept. Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: Emanuel, R E
EM: emanuelre@appstate.edu
AF: Department of Geology Appalachian State University, 572 Rivers St., Boone, NC 28608, United States
AU: Muth, D J
EM: djm7f@virginia.edu
AF: Department of Environmental Sciences University of Virginia, 291 McCormick Rd., Charlottesville, VA 22904, United States
AU: Epstein, H E
EM: hee2b@virginia.edu
AF: Department of Environmental Sciences University of Virginia, 291 McCormick Rd., Charlottesville, VA 22904, United States
AU: Welsch, D L
EM: dwelsch@frostburg.edu
AF: Department of Geography Frostburg State University, 211 Gunter Hall, Frostburg, MD 21532, United States
AU: Pacific, V J
EM: vincent.pacific@myportal.montana.edu
AF: Dept. Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: Wraith, J M
EM: jwraith@montana.edu
AF: Dept. Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AB: Soil temperature plays an important role in many model representations of soil CO₂ production and transport. However, interactions among environmental variables such as temperature and soil moisture may introduce uncertainty into these models. Among the sources of uncertainty in models of soil CO₂ production and transport is daily hysteresis between soil CO₂ flux and soil temperature. We quantified the degree to which hysteresis between soil [CO₂] and soil temperature is controlled by soil water content in a montane conifer forest, and how this nonlinearity impacts estimates of soil CO₂ efflux. Based on chamber measurements at our site, a developed Q10 relationship overestimates CO₂ flux by 42 g C m-2 (19%) for the entire growing season due to its inability to account for the daily cycle of soil [CO₂], the variability of soil moisture, and moisture-dependent diffusive transport of CO₂ through the soil column. Only under late- season dry conditions is the Q10 relationship able to predict CO₂ flux. We found that at high levels of soil water content, hysteresis imposes organized, daily variability in the relationship between soil [CO₂] and soil temperature, and at low levels of soil water content, hysteresis is minimized. Our results demonstrate that diurnal hysteresis between soil [CO₂] and soil temperature is due mostly to the balance (or imbalance in wet soils) between production and diffusion. The seasonality in soil moisture controls the transition from an imbalanced system (where diurnal hysteresis is observed) to a balanced system (no diurnal hysteresis observed). The magnitude of hysteresis in the soil [CO₂] – soil temperature relationship is an important indicator of the existence of concomitant, yet independent, autotrophic and heterotrophic soil [CO₂] processes. As such, the role of soil water content in controlling the relationship between soil [CO₂] and soil temperature should be considered when modeling the dynamics of carbon cycling in ecosystems with strong seasonality in soil water content.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1813 Eco-hydrology
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Fall Meeting