HR: 1340h
AN: B53A-0945    [Abstracts]
TI: Analysis of Methane and Carbon Dioxide Fluxes in Forest Soils Using Concentration and Stable Carbon Isotope Ratio Gradients
AU: Lee, K
EM: kernlee@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, Victoria, BC V8W 2Y2, Canada
AU: * Whiticar, M J
EM: whiticar@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, Victoria, BC V8W 2Y2, Canada
AB: The importance and mechanisms of methane/carbon dioxide exchange between forest soils and the atmosphere continue to be debated. We have conducted summer fieldwork in 2005 and 2006 to collect and analyse soil gas samples from forest locations in Quebec and British Columbia. Carbon isotope ratios and concentration soil profiles for both CH₄ and CO₂ are determined using GC-IRMS to clarify carbon fluxes within these forest soils. Initial observations of δ¹³C and concentration gradients of CO₂ show a increase in [CO₂] and decrease in δ¹³CO₂ with soil depth. These trends are indicators of both net CO₂ production in and efflux from these forest environments. In contrast, the CH₄ data show increasing δ¹³CH₄ and decreasing [CH₄] with increasing soil depth. This indicates that the soils at both locations act as net sinks of atmospheric methane. Chamber flux measurements provide further support for this conclusion. They show a net accumulation of CO₂ accompanied by a decrease in CH₄ concentration with time in the chamber headspace. In addition, the CH₄ is ¹³C-enriched while the CO₂ is ¹³C-depleted in the chamber experiments. Variations present within the soil CH₄ and CO₂ profile indicate a non-uniform distribution of methane-oxidizing potential within the soil column. Furthermore, flux estimates using the chamber gas concentration data reveal large temporal and spatial variations in fluxes within the same location, potentially due to local heterogeneities in site characteristics.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0490 Trace gases
DE: 1055 Organic and biogenic geochemistry
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1865 Soils (0486)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting