Terminal Electron Acceptors for Controlling Methane Emissions from Submerged Rice Soils

Abstract

Wetland rice fields are source of atmospheric methane. Methane is formed following reduction of carbon dioxide by hydrogen and through decarboxylation of acetate in anaerobic soils under reduced conditions. Methane production requires flow of carbon and electrons to microbial population of methanogens under reduced conditions in the strict absence of free oxygen. Application of or in-situ availability of terminal electron acceptors (oxidants) such as ferric iron or sulfate allows iron or sulfate reducers to successfully compete for substrates, hydrogen or acetate, with methanogens. This stops methane production. Electron acceptors also oxidize methane and reduce its emission. Since iron redox system plays a dominant role in tropical rice soils, which are rich in iron, the role of iron oxides and hydroxides as electron acceptor for controlling methane emission from wetland rice fields deserves more attention. For mitigating methane emission from wetland rice fields, ferric iron as a terminal electron-accepting agent, can either be added to the soil or regenerated in the soil by manipulating redox potential through soil and water management. Examples are given from recent literature illustrating the role of electron acceptors (ferric iron, sulfate, etc.) in reducing methane emission from submerged rice soils. The need for future research is also examined.