Carbon dioxide reduction methanogenesis

Sulphate reduction in marine sediments is often the dominant form of carbon remineralisation, and contributes most of the alkalinity observed in the sediment pore-water. When concentrations of sulphate fall below 35 to 40 pM, carbon dioxide reduction by methanogens may begin, whereas sulphate levels below about 30 pM are required before the onset of acetate-type reduction reactions that dominate methanogenesis (Kuivila et al., 1989). Carbon dioxide reduction is usually only evident in the sulphate reduction zone, where bicarbonate is produced, but it can contribute about 65% of the methane flux at its peak (Crill Martens, 1986). 

Capone, D.G., Reese, D.D., and Kiene, R.P., Effects of metals on methanogenesis, sulfate reduction, carbon dioxide evolution, and microbial biomass in anoxic salt marsh sediments, Appl Environ Microbiol, 45 (5), 1586-1591, 1983. 

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