Biological CH4 oxidation is hugely important in reducing CH4 emissions from 'source' areas such as landfills, marshland and lakes. Although vast amounts of CH4 may be produced in these areas, methanotrophs can often limit the actual release of CH4 to the atmosphere to less than 10%. Indeed, biological oxidation of CH4 is probably greater than total chemical oxidation in the atmosphere if the full CH4 cycle is considered (King, 1992). De Visscher et al. (Chapter 12, this volume) describe the important CH4 sinks in human-made environments. In the soils above landfill sites, for instance, large and very active populations of high-capacity methanotrophs can develop, using much of the CH4 that diffuses up through the soil from the decomposing rubbish (Whalen et al., 1990). Although the focus of their chapter is on landfill cover soils, which are the clearest examples of such artificial CH4 sinks, De Vissceher et al. also discuss the more general importance of such 'artificially induced' CH4 oxidation.
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