Stable Isotopic Studies of Bacteriogenic Methane Emissions

Methane is produced thermogenically from organic matter, associated with oil and coal production, and bacteriogenically by two main biochemical pathways, CO2 reduction and acetoclastic methanogenesis (commonly known as fermentation), CH4 emissions can be an environmental problem on a local scale, due to the explosive potential of CH4, and on a global scale as it is an effective radiatively forcing greenhouse gas, with continued emissions to the atmosphere contributing to potential global warming. Stable isotopic characterisation of sources can be used, when monitoring the composition of atmospheric CH4 and its secular trend, to provide constraints on the relative magnitude of fluxes (Stevens, 1988). The overall flux isotopic composition should correspond to the isotopic composition of the gas in the atmosphere, once fractionation associated with atmospheric loss processes has been accounted for (Stevens and Engelkemeir, 1988). At present, delta13C characterisation of CH4 sources is well established. By comparison, deltaD characterisation of global sources of CH4 is poorly established and the atmospheric chemistry complex. This research utilised stable isotope analyses of bacteriogenic CH4 to constrain the isotopic signature of both carbon and hydrogen, and, where possible, to understand the factors controlling that signature. (Abstract shortened by ProQuest.)