Methane Release from Land and Land Use-significance and Mitigation Options
The rise of the atmospheric concentration of methane(CH4)contributes significantly to global warming.Despite itssignificance,recent data document a slowdown in the rate of increase of atmospheric CH4.The reasons of this decreasingrate are not known.China hosts ecosystems and land use types that are important for the global CH4 budget.Among these,rice paddies,wetlands,and landfills are of particular importance.In this contribution,I present CH4 emissions as well as mitigation options from these ecosystems and land rise types.The most recent IPCC report shows that biogenic CH4 emissions(by methanogenic bacteria)make up 70％ of the global CH4 release,with non biogenic sources responsible for the rest.Rice paddies release 31-112 Tg CH4 yr-1,naturalwetlands emit 100-231 Tg CH4 yr-1,and landfills are a source of 35-65 Tg CH4 yr-1.It is estimated that, of 7.67 Tg CH4 yr-1 that are released by rice cultivation in China, 70.4％ originate from irrigation and 27.5％ from rainthd production. If appliad to the entire rice growing area in China, the recent reduction in CH4 release due to the introduction of midseason paddy drainage amounts to 5 Tg annualy. Following investigations from India and Indonesia low soil organic matter and high pH(>6)may result in a further reduction of CH4 release due to rice growing.Depite its importance (70％ of the global wetland CH4 release) tropical and subtropical wetlands have been examined very little compared to northern wetlands. The catastrophe of burning peatlands in Kalimantan (Indonesias) as a consequence of the Mega Rice project led to a carbon dioxide (CO2) release of 0.6-2.6*109 t CO2-C in 1997. Thus,drainage reduces CH4 cmissions from wetlands to 0, but is accompanied by CO2 emissions with a much higher radiative foreing. On the other hand, some elements of envionmental pollution may inadvertently reduce CH4 emissions: In areas of high sulfate deposition, sulfate reducing bacteria outcompete methanogenic bacteria, thus inhibiting methanogenesis and CIL, emissions by up to 47.5％. Already, sulfate emissions have reduced the global CH4 souse by 5 Tg below preindustrial levals. In global warming scenarios,this effect may halve the rise of CH4 emissions in wetlands (15 Tg instead of 30 Tg)The CH4 source in landfils is also a resull of the decomposition of orgainc mater. While in many countries, cover soils and landfill caps are not designed with CH4 oxidation in mind, in Germany, a set of measures has resulted in a drastic reduction of CH4 release from landfills.These measures include most importantly the pre-treatment of waste, but also the recovery of dry materials, gas-tight sealing of landfills, and the capture of remaining produced CH4. Due to these measures, the waste sector met the German goal of reducing greenhouse gas emissions by 18％.In summary, the presented ecosystems and land use types have shown a considerable potential in the reduction of CH4 emissions.Some of the emission reductions were implemented deliberately, others as an inadevertent side effect of human manipluations of the natural ennvironment. In all cases, it can ha seen that human interventions are able to substantially reduce the CH4 emissions from many important sources.
Stephan Glatzel
Faculty of Agricultural and Environmental Sciences,Landscape Ecology and Site Evaluation,University of Rostock,Rostock,18069,Germany
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2008-06-05（万方平台首次上网日期，不代表论文的发表时间）