Wetlands are an important natural source of methane to the atmosphere. The amounts of methane produced vary greatly from area to area, with temperature, water level and organic carbon content all being important controlling factors.

Current estimates of global methane emission from wetlands range between 100-250 million tonnes of methane per year, equivalent to around a quarter of total global methane emissions.

The process of methane production (methanogenesis) involves the microbial mineralization of organic carbon under anaerobic conditions in the waterlogged soil by microorganisms called Archaea. When water levels fall, as they often do in the Summer months, methane emission from wetlands can be greatly reduced or even cease completely as oxygen concentrations rise in the soil.

Human Impact

Through widespread land drainage and changes in land-use, man has had a great impact on wetland methane emissions in many areas of the world. Additionally, increased nitrogen deposition from the atmosphere, again resulting from human activity, may also greatly increase net methane emissions from wetland areas by inhibiting any methane consumption (methane oxidation).

Potential for control

The potential for control of methane emission from wetlands lies largely in land-use policy. Under certain circumstances draining of wetlands could greatly reduce methane emissions. However, certain wetland environments, such as peat bogs, have been shown to vastly increase their emissions of Carbon dioxide in response to such draining - so offsetting any net cut in GHG emissions. On top of this there is the problem of habitat destruction, with many wetland animal, plant and insect species already being endangered.

Overall, decisions as to whether to lower wetland water tables, and so methane emission, by increased drainage or tree planting must be made on an individual wetland basis.