Methane wetlands

Many physical, chemical, and biological factors of soil influence the production and emission of nitrous oxide and methane. Wetland hydrology and hydroperiod determine whether soil aerobic or anaerobic conditions exist. Redox status is a quantifiable measurement of the reduction process occurring in wetlands. It is well known that nitrous oxide is mainly produced through denitrification and nitrification at moderately reducing conditions, but methanogenesis occurs only under strictly anaerobic conditions. 

Controlling methane release from wetland, rice paddies and gaseous emissions from animals is more problematic. The release from rice paddies and wet lands is slow, intermittent and takes place over a wide geographic area, and thus very difficult to control. Gaseous emissions from agricultural animals contribute to atmospheric accumulation of methane due to fermentative digestion that produces methane in... 

Longer ice-core records show that methane concentrations have varied on a variety of time scales over the past 220 000 years (Fig. 18-15) Qouzel et al, 1993 Brook et al, 1996). Wetlands in tropical (30° S to 30° N) and boreal (50° N to 70° N) regions are the dominant natural methane source. As a result, ice-core records for preanthropogenic times have been interpreted as records of changes in methane emissions from wetlands. Studies of modem wetlands indicate that methane emissions are positively correlated with temperature, precipitation, and net ecosystem productivity (Schlesinger, 1996). 

Conrad R. Control of microbial methane production in wetland rice fields. Nutr. Cycl. Agroecosys. 2002 64 59-69. 

Denier van der Gon HAC, van Breemen N, Neue HU, Lantin RS, Aduna JB, Alberto MCR, Wassmann R. 1996. Release of entrapped methane from wetland rice fields upon soil drying. Global Biogeochem. Cycl. 1996 10 1-7. 

Whiting GJ, Chanton JP. Primary production control of methane emission from wetlands. Nature. 1993 364 794-795. 

Air bubbles in the ice corroborated the increased wetness in other areas. The amount of methane in the bubbles indicates that this gas was entering the atmosphere 50 percent faster during the warming than it had earlier. The methane probably entered the atmosphere as wetlands flooded in the tropics and ice and snow thawed in the north. 

Aselmann 1, Crutzen PJ. 1989. Global distribution of natural fresh-water wetlands and rice paddies their net primary productivity, seasonality and possible methane emissions. Journal of Atmospheric Chemistry 8 307-358. 

Bachelet D, Neue HU. 1993. Methane emissions from wetland rice areas of Asia. Chemosphere 26 219-237. 

Cao MK, Gregson K, Marshall S. 1998. Global methane emission from wetlands and its sensitivity to climate change. Atmospheric Environment 32 3293-3299. 

Conrad R. 1993. Mechanisms controlling methane emission from wetland rice fields. In Oremland R, ed. Biogeochemistry of Global Change. Radiatively Active Gases. New York Chapman HaU, 317-355. 

Segers R. 1998. Methane production and methane consumption a review of processes underlying wetland methane fluxes. Bio geochemistry 41 23-51. 

Methane is produced by bacteria under anaerobic conditions in wet environments such as wetlands, swamps and rice fields. It is also produced in the stomachs of cattle and by termites. Typical anthropogenic sources are from fossil fuels such as coal mining and as a byproduct in the burning of biomass. The latter sources are considerably heavier in C than the former. Recently, Keppler et al. (2006) demonstrated that methane is formed in terrestrial plants under oxic conditions by an unknown mechanism. The size of this methane source is stiU unknown but it might play an important role for the methane cycle. 

Wania R. Prentice C. Harrison S. Homibrook E. Gedney N. Christensen T. and Clymo R. (2004). The role of natural wetlands in the global methane cycle. EOS, 85, 466. 

Chanton, J.P., Martens, C.S., and Kelley, C.A. (1989a) Gas transport from methane-saturated, tidal freshwater and wetland sediments. Lirnnol. Oceanogr. 34, 807-819. 

Chanton, J.P., Smith, C.J., and Patrick, W. (1993) Methane release from Gulf coast wetlands. Tellus 35, 8-15. 

King, G.M. (1990) Regulation by light of methane emissions from a wetland. Nature 345,513-515. 

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