Rice paddies, methanogenesis

The total flux of CH4 to the atmosphere today is about 34 x 1012 moles y1 about 20% of this flux results from enteric fermentation processes in animals, termites, and humans. Of the remaining flux, about 60% comes from the process of methanogenesis in sediments of various types-primarily muds of rice paddy fields, swamps, and marshes. The overall bacterial reactions in sediments are the disproportionation of organic matter to CH4 and CO2, that is ... 

There have been remarkably few attempts to determine the contribution of Fe(III) reduction to anaerobic carbon metabolism in freshwater ecosystems where it may be the dominant pathway. The most extensive such study examined 16 rice paddy soils collected from China, Italy, and the Philippines (Yao et al., 1999). Fe(III) reduction was 58-79% of carbon metabohsm during the reduction phase (Section 8.08.8.1), with most of the remainder attributed to methanogenesis. Fe(III) reduction contributed —70% of the anaerobic metabolism in a Juncus effusus marsh (Roden and Wetzel, 1996). 

Frenzel P., Bosse U., and Janssen P. H. (1999) Rice roots and methanogenesis in a paddy soil ferric iron as an alternative electron acceptor in the rooted soil. Soil Biol. Biochem. 31, 421-430. 

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