Production and consumption of methane in freshwater lake ecosystems.

The atmospheric concentration of methane (CH(4)), a major greenhouse gas, is mainly controlled by the activities of methane-producing (methanogens) and methane-consuming (methanotrophs) microorganisms. Freshwater lakes are identified as one of the main CH(4) sources, as it was estimated that they contribute to 6-16% of natural CH(4) emissions. It is therefore critical to better understanding the biogeochemical cycling of CH(4) in these ecosystems. In this paper, the effects of environmental factors on methanogenic and methanotrophic rates are reviewed and an inventory of the methanogens and methanotrophs at the genus/species level in freshwater lakes is given. We focus on the anaerobic oxidation of methane, which is a still poorly known process but increasingly reported in freshwater lakes.