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Abstract. Field measurement of landfill methane (CH 4 ) emissions indicates natural variability spanning more than seven orders of magnitude, from less than 0.0004 to more than 4000 g/m 2 per day. This wide range reflects net emissions resulting from production (methanogenesis), consumption (methanotrophic oxidation), and gaseous transport processes. The determination of an ‘average’ emission rate for a given field site requires sampling designs and statistical techniques which consider spatial and temporal variability. Moreover, particularly at sites with pumped gas recovery systems, it is possible for methanotrophic microorganisms in aerated cover soils to oxidize all of the CH 4 from landfill sources below and, additionally, to oxidize CH 4 diffusing into cover soils from atmospheric sources above. In such cases, a reversed soil gas concentration gradient is observed in shallow cover soils, indicating bidirectional diffusional transport to the depth of optimum CH 4 oxidation. Rates of landfill CH 4 oxidation from field and laboratory incubation studies range up to 166 g/m 2 per day, among the highest for any natural setting, providing an effective natural control on net emissions. It has been shown that methanotrophs in landfill soils can adapt rapidly to elevated CH 4 concentrations with increased rates of CH 4 oxidation related to depth of oxygen penetration, soil moisture, and the nutrient status of the soil. Estimates of worldwide landfill CH 4 emissions to the atmosphere have ranged from 9 to 70 Tg/y, differing mainly in assumed CH 4 yields from estimated quantities of landfilled refuse. At highly controlled landfill sites in developed countries, landfill CH 4 is often collected via vertical wells or horizontal collectors. Recovery of landfill CH 4 through engineered systems can provide both environmental and energy benefits by mitigating subsurface migration, reducing surface emissions, and providing an alternative energy resource for industrial boiler use, on‐site electrical generation, or upgrading to a substitute natural gas. Manipulation of landfill cover soils to maximize their oxidation potential could provide a complementary strategy for controlling CH 4 emissions, particularly at older sites where the CH 4 concentration in landfill gas is too low for energy recovery or flaring. For the future, it is necessary to better quantify net emissions relative to rates of CH 4 production, oxidation, and transport. Field measurements, manipulative studies, and model development are currently underway at various spatial scales in several countries
Bogner et al. (Mon,) studied this question.