Methane Emission from Natural Wetlands in China: Summary of Years 1995–2004 Studies

• Published in: Pedosphere Vol. 17; no. 4; pp. 475 - 486
• Main Authors: DING, Wei-Xin, CAI, Zu-Cong
• Format: Journal Article
• Language: English
• Published: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 China 01.08.2007
• Subjects: Freshwater; China, People's Rep; seasonal variation; diel variation; methane emission; wetland; temporal variation
• ISSN: 1002-0160; 2210-5107
• DOI: 10.1016/s1002-0160(07)60057-5

From studies undertaken during 1995-2004, annual budgets of CH sub(4) emissions from natural wetlands and its temporal and spatial variations were examined throughout China, and various factors influencing CH sub(4) emissions were also evaluated. The seasonal variation in CH sub(4) emissions that increased with increasing plant growth reached its peak in August; decrease in the emissions was found in freshwater marshes but not in peatlands. Emissions were mainly controlled by temperature and depth of standing water. Low CH sub(4) emissions at the early plant growing stages were not because of deficiency of organic C for CH sub(4) production but because of low temperatures. Low temperatures not only reduced CH sub(4) production but also stimulated CH sub(4) oxidation by lowering the activity of other aerobic microbes which left more O sub(2) in the rhizosphere for methanotrophs. Low summer temperatures (below 20 degree C) in the Qinghai-Tibetan Plateau lowered CH sub(4) production and CH sub(4) emission resulting in little or no seasonal variation of emissions. Diel and spatial variation in CH sub(4) emissions depended on plant species. For plants that transport CH sub(4) using the pressure-driven convective through-flow mechanism, diel variation in CH sub(4) emissions was governed by diel variation of solar energy load (that produces temperature and vapor pressure differences within various plant tissues) and stomatal conductance. For plants that transport gases using the molecular diffusion mechanism only, the diel variation of CH sub(4) emissions was because of differences in the magnitude of O sub(2) produced through photosynthesis and then delivered into the rhizomes and/or rhizosphere for CH sub(4) oxidation. Emergent plants could transport more CH sub(4) than submerged plants because the former transport CH sub(4) directly into the atmosphere rather than into water as do submerged plants where CH sub(4) can be further be oxidized during its diffusion from water to the atmosphere. Emergent plants with high gas transport capacity could not only transport more CH sub(4) into the atmosphere but also live in deeper water, which in turn would inundate more plant litter, resulting in increased availability of C for CH sub(4) production. Annual CH sub(4) emission from natural wetlands in China was estimated to be 1.76 Tg, up to 1.17 Tg of which was emitted from freshwater marshes. CH sub(4) emission from freshwater marshes mainly occurred during the growing season and less than 8% was released during the freeze-thawing period despite the fact that thawing efficiently released CH sub(4) fixed in ice column into the atmosphere.