Human activities emitting methane include leaks from natural gas systems and the raising of livestock. (epa.gov)
Flooded rice paddies also emit methane because water prevents oxygen from reaching the soil, triggering a build - up of methane - emitting bacteria. (insideclimatenews.org)
Wetlands emit methane because of anaerobic degradation of organic material by micro-organisms. (environmentalresearchweb.org)