Analysis of carbon dioxide and methane cycling in forest soils using stable carbon isotopes




Lee, Kern Young

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Understanding the role of forests in the cycling of methane (CH4) and carbon dioxide (CO2) is of importance to the elucidation of global greenhouse gas budgets. Previous studies have shown aerated forests soils to be net sinks of atmospheric CH4 and sources of carbon dioxide. While much research has focused on the role of forest soils as CO2 sources and CH4 sinks, few studies have utilized 13C-isotope studies to clarify the nature of subsurface CO2 production and CH4 consumption. The present study, carried out in 3 temperate forest environments on Vancouver Island during 2006 and 2007, and a boreal forest in northern Quebec in 2005, is intended to address this paucity of information. The isotope and concentration data corroborates previous studies in suggesting that both temperate and boreal forest environments act as net CH4 sinks and CO2 sources. No clear evidence of methanogenesis is apparent in either Vancouver Island or northern Quebec, where the isotopic composition of subsurface CH4 is influenced by diffusive and biological fractionation. Near-surface photosynthetic uptake may have a strong influence on the isotopic composition of soil CO2 and the resultant fluxes, acting to reduce apparent fluxes due to CO2 consumption. Intra-site variability of CH4 and CO2 fluxes indicates that the use of two static chambers in a single site, while sufficient for the confirmation of gas uptake or emission, may be less adequate in the determination of actual rates of efflux/influx. Future studies should address this by either sampling a larger area, installing a greater number of chambers, or by utilizing entirely different methods, such as the use of eddy covariance techniques.



Stable Isotopes, Methane, Carbon Dioxide, Global Change