As noted near the end of the article, the introduction of ammonium sulfate to active rice paddies shifts the bacterial population away from those producing methane. Directly adding ammonium sulfate would, if this actually accounts for a reduction in methane emissions and doesn't adversely impact crop yields could be a useful mitigation strategy.
Reducing sulfur dioxide emissions to control air pollution still outweighs the disadvantages of not doing it. Since the methane in the Arctic sediments has already been produced and any increases are probably insignificant relative to existing deposits, the use of stratospheric or even upper tropospheric sulfate based aerosols there would have no impact on the amount of methane that could be released as the sediments warm. The aerosol deposition would occur over a broad area and mostly add to the sulfate concentration in the water, which is probably already well buffered relative to sulfate ion. Given that the shallowest of these so-called shallow sediments are stll under upwards of 100 ft of water, I also doubt the aerosols would have much of an impact on cooling the sediments except over very long periods of time, perhaps hundreds of years. http://www.ghgonline.org/methanerice.htm Methane Sources - Rice Paddies At between 50 and 100 million tonnes of methane a year, rice agriculture is a big source of atmospheric methane, possibly the biggest of man-made methane sources. The warm, waterlogged soil of rice paddies provides ideal conditions for methanogenesis, and though some of the methane produced is usually oxidized by methanotrophs in the shallow overlying water, the vast majority is released into the atmosphere. Rice is grown very widely and rates of methane emission may vary greatly between different areas. Differences in average temperature, water depth and the length of time that the rice paddy soil is waterlogged can all result in big regional variations. However, methane emission from worldwide rice agriculture has been well studied in recent years and fairly reliable estimates of global emissions now exist. Emissions from rice paddies can vary hugely during the course of a year. On average, the rice paddy soil is only fully waterlogged for about 4 months each year. For the rest of the time methanogenesis is generally much reduced and, where the soil dries out sufficiently, rice paddy soil can become a temporary sink for atmospheric methane. Human Impact Clearly, humans are directly responsible for the world's paddy fields and so also for their methane emissions. The expansion of the human population has necessitated increased rice production and so methane emission from this source. There are, though, strategies which may lessen our impact via this greenhouse gas source as outlined below. Potential for control With an increasing world population, reductions in rice agriculture remain largely untenable as on methane emission reduction strategy. However, through a more integrated approach to rice paddy irrigation and fertilizer application substantial reductions remain possible. Many rice varieties can be grown under much drier conditions than those traditionally employed, with big reductions on methane emission without any loss in yeild. Additionally, there is the great potential for improved varieties of rice, able to produce a much larger crop per area of rice paddy and so allow for a cut in the area of rice paddies, without a cut in rice production. Finally, the addition of compounds such as ammonium sulphate, which favour activity of other microbial groups over that of the methanogens, has proved successful under some conditions. ----- Original Message ----- From: Renaud_de_RICHTER To: Alvia Gaskill Sent: Friday, October 03, 2008 7:09 AM Subject: Methane Emissions from Rice Paddies Reduced 24% by Acid Rain Alvia, I don' know if this could also apply to methane release from permafrost melting. If it's the case, Crutzen idea could be reinforced... related to "shallow shelf hydrates" post to the geoengineering group by Collin Forest Regards Renaud Methane Emissions from Rice Paddies Reduced by Acid Rain Friday, 03 October 2008 Article by WorldNews.com Correspondent Vlad Jecan - [EMAIL PROTECTED] http://article.wn.com/view/2008/08/07/Methane_Emissions_from_Rice_Paddies_Reduced_by_Acid_Rain/ China is the world's largest producer of rice and the methane emissions from rice paddies have grown to an alarming rate. But scientists discovered that acid rain can reduce methane emissions by about 24 per cent. Acid rains are caused by excessive atmospheric pollution and methane is 21 times more powerful than carbon dioxide as a greenhouse gas. According to a recent study, the narrowing of methane emissions happen when the rice plant is producing grain, this being the stage when most methane emissions come from rice. After scientists simulated an acid rain, they found out that it reduces methane emissions by 24 per cent. Researchers used Portuguese rice soils and grain, with very low or non existent acid rain influence, which are very similar to the Asian rice soils before pollution. Adding small doses of sulphate, the scientists managed to simulate an acid rain experience very similar to polluted areas in China. Acid rains are of extreme importance in China, and other parts of Asia. The once clean and healthy soil is now contaminated, but the research team who discovered the effects of acid rains on methane emissions from rice paddies say that this beneficial side effect should not be ignored. In the next years, the scientists may manage to find a way to reduce the frequency of acid rains or to eliminate them. Additionally, new ways are being researched to cut the methane emissions which are extremely dangerous as greenhouse gases. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
