Significance of anaerobic oxidation of methane (AOM) in mitigating methane emission from major natural and anthropogenic sources: a review of AOM rates in recent publications

Abstract

Methane is estimated to have contributed 20% of postindustrial global warming. Methanotrophs oxidize methane and curb methane emissions into the atmosphere. Anaerobic oxidation of methane (AOM) has been recognized as an important methane sink. Sulfate is the primary electron acceptor of AOM in the marine environment, while nitrite/nitrate is encountered more often in terrestrial water-logged systems, such as rice paddy and wetlands. A key aspect of AOM is the reaction rate, which influences methane fluxes to the oxic zones and eventually the atmosphere. We collated the AOM rates from major natural and anthropogenic sources in recent publications and found that AOM rates are generally lower than the corresponding aerobic methane oxidation rates in wetlands and rice paddy, while the AOM rates are often higher than the corresponding aerobic oxidation rates in freshwater systems and marine environments. Based on the median reaction rates and estimated aerobic and anoxic zone coverages, AOM consumes approximately 71%, 8%, 5%, 13%, and 3% of the methane entering the anoxic zones in oceans, wetlands, paddy systems, lakes/reservoirs, rivers, respectively. These analyses suggest that AOM is a key methane sink in oceans, while aerobic methanotrophs consume more methane in the other studied ecosystems. Finally, the controlling factors of AOM and some issues in the rate quantification were discussed. It is believed that more comprehensive studies of AOM and improved rate quantification would assist in forecasting methane emission, which fosters scientific debate over global warming and eventually affects climate policymaking.