Rice paddies, atmospheric

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... 

Cicerone RJ, Shetter JD. Sources of atmospheric methane Measurements in rice paddies and a discussion. J. Geophys. Res. 1981 86 7203-7209. 

Recent estimates indicate that the level of carbon dioxide in the atmosphere has increased by a third since the beginning of the industrial age, and that it contributes significantly to global warming. Other major contributors include methane, tropospheric ozone, and nitrous oxide. Methane is the principal component of natural gas, but it is also produced by other sources such as rice paddies and farm animals. Tropospheric ozone is generated naturally and by the sunlight-... 

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. 

Holzapfel-Pschorn A, Seiler W. 1986. Methane emission during a cultivation period from an Italian rice paddy. Journal of Geophysical Research-Atmospheres 91 1803-1814. 

Seiler W, Holzapfel-Pschom A, Comad R, Scharffe D. 1984. Methane emission from rice paddies. Journal of Atmospheric Chemistry 1 241-268. 

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 ... 

It is estimated that about 500 million tons of methane are being added to the air each year (Craig and Chou, 1982), largely by anaerobic production in rice paddies and wetlands as well as from the metabolism of ruminant domestic animals and, possibly, African termites (Rasmussen and Khalil, 1981 Zimmerman et d., 1982). This gas is slowly oxidized by reactions with Hydroxyl free radical. Its atmospheric content is around 5 gigatons, indicating that the residence time in the atmosphere is about 10 years. As Figure 12 shows, since 1965 the atmospheric concentration of methane has increased by about 3096. If this rate continues, the methane concentration will have doubled early in the 21st century. 

Although forests are obvious as sources of gas, it is the microorganisms that are especially important in generating atmospheric trace gases. Methane, which we have already discussed, is generated by reactions in anaerobic systems. Damp soils, as found in marshes or rice paddies, are important micro-biologically dominated environments, as are the digestive tracts of ruminants such as cattle. 

The simplest alkane is methane (CH4). Methane oxidation is the essential chemistry of the background troposphere (Logan et al., 1981 Thompson and Cicerone, 1986). Ice-core records show that methane concentrations in the atmosphere have more than doubled since preindustrial times (Khalil and Rasmussen, 1987), reaching a rate of increase of 1% yr-1 in the last decade (Khalil et al., 1989). Methane is emitted to the atmosphere by ruminants, wetlands, tundra, open waters, termites, rice paddies, biomass burning, natural gas production, and coal mining [see Jacob (1991) for a review of the literature on methane sources] the principal sink of CH4 is reaction with OH. 

The second major greenhouse gas is CH4 which is produced by the anaerobic decomposition of organic material the old name of marsh gas came about because bubbles of CH4 escape from marshes. Flooded areas such as rice paddy fields produce large amounts of CH4, and ruminants (e.g. cows, sheep and goats) also expel sizeable quantities of CH4. Although the latter is a natural process, recent increases in the numbers of domestic animals around the world are naturally leading to increased release of CH4 into the atmosphere. 

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