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How do wetlands produce methane?

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World map shaded to show annual carbon dioxide emissions by country in 2022, with China, the United States, and India highlighted as top emitters in dark red. A bar chart below lists the top ten emitting countries by million metric tons. — Greenhouse gas Map of annual carbon dioxide emissions by country in 2014.

In wetlands, methane is produced through the anaerobic bacterial decomposition of organic matter, such as vegetable material, occurring under water.12

This process is carried out by highly specialized, obligately anaerobic microorganisms known as methanogens, which are members of the domain Archaea. Because these organisms are sensitive to oxygen, they thrive in the oxygen-depleted (anaerobic) environments found in wetlands, such as swamps and marshes.13

During this decomposition, other anaerobic bacteria first break down complex organic materials into simpler substances like acetate, carbon dioxide, and hydrogen gas. Methanogens then utilize these products—primarily by using carbon dioxide as a terminal electron acceptor and hydrogen gas as an electron donor—to generate methane (CH $_{4}$ ) as a metabolic by-product. By consuming the hydrogen gas produced by other bacteria, methanogens also help stimulate the overall metabolic activity of the microbial community in these environments.13