Topic
Atmospheric methane
About: Atmospheric methane is a research topic. Over the lifetime, 2034 publications have been published within this topic receiving 119616 citations.
Papers published on a yearly basis
Papers
More filters
••
TL;DR: In this paper, seasonal and spatial variation of dissolved and atmospheric methane (CH 4 ) was measured in the estuaries of the Sundarban mangrove ecosystem from January to December 2003.
115 citations
••
TL;DR: In this article, chemical kinetic relationships are established between the bacteriamediated anaerobic decomposition of humic matter, the mean residence time (MRT) of humus, and methane fluxes.
Abstract: On the basis of 17 ecosystems, it is estimated that 9.1×1014 g CH4/year are emitted into the atmosphere from the biosphere. Enteric fermentation in animals and humans, decomposition of organic wastes, and biomass burning contribute an additional 2.0×1014 g CH4/yr. Various fossil sources emit another 1×1014 g CH4/yr. When all sources are considered, they emit 12.1×1014 g CH4 each year. As with earlier inventories, this study indicates that the fossil methane contribution is less than 10% of the total annual global production rate. Chemical kinetic relationships are established between the bacteriamediated anaerobic decomposition of humic matter, the mean residence time (MRT) of humus, and methane fluxes. These equations and the 14C specific activity are used to obtain an average MRT of 1365 years for the earth's 1.8×1018 grams of humic carbon. Use of the global methane production rate and the concentration of atmospheric methane results in an average 3.3 year residence time and an average global hydroxyl radical concentration of 2.7×106 per cm3.
115 citations
••
TL;DR: It has now become possible to isolate, detect and characterize the methanogens and methanotrophs by using molecular biological tools like PCR, FISH, etc.
Abstract: Methane has profound impact on the physico-chemical properties in atmosphere leading to global climate change. Out of the various sources of CH4, rice fields are the most significant contributors. The processes involved in the emission of CH4 from rice fields to the atmosphere include CH4 production (methanogenesis) in the soil by methanogens, methane oxidation (methanotrophy) by methanotrophs and vertical transfer of CH4 via plant transport and diffusion or ebullition. In the overall methane dynamics rice plants act as : a) source of methanogenic substrate, b) conduit for CH4 through well developed system of inter cellular air space (aerenchyma), and c) potential methane oxidizing micro-habitat in the rhizosphere by diffusing oxygen which favour the growth and multiplication of methanotrophs. Apart from mechanistic uncertainties, there are several other uncertainties in the estimation of CH4 flux. Methane dynamics in the paddy field is controlled by a complex set of parameters linking the biological and physical characteristics of soil environment like temperature, carbon source, Eh, pH, soil microbes and properties of rice plants, etc. It has now become possible to isolate, detect and characterize the methanogens and methanotrophs by using molecular biological tools like PCR, FISH, etc. techniques. The apparent half saturation constant (Km) and maximum oxidation rate (Vmax) are distinctive parameters which determine the ability of bacteria to survive on atmospheric methane. Keywords. methane; methanotrophs; methanotrophy; methanogens; molecular tools
113 citations
••
TL;DR: Using a combination of field sampling, incubation experiments, and modeling, this paper showed that the recurring midwater methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones.
Abstract: The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m22 d21. Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0–20% dissolved oxygen (DO) in the bottom water, and a positive gradient within $ 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle. Methane accounts for 20% of the total radiative forcing among all long-lived greenhouse gases and has an estimated global warming potential 25 times that of CO2 in the coming century (Forster et al. 2007). Balancing the global methane budget, however, remains problematic due to uncertainty in its sources and sinks (Conrad 2009; Bastviken et al. 2011). Besides geological and anthropogenic emissions, methane is also produced by methanogens via three major pathways: acetoclastic, methylotrophic, and hydrogenotrophic methane production (Mah et al. 1977). Many of the enzymes involved are believed to be sensitive to oxygen (Jarrell 1985). Accordingly, a longstanding paradigm is that biological production of methane occurs exclusively under anoxic conditions (Mah et al. 1977). Recent studies suggested that terrestrial plants may emit methane under aerobic conditions (Keppler et al. 2006), and saprotrophic fungi are able to produce methane independently of methanogenic archaea (Lenhart et al. 2012). Hence, the methane cycle appears to be more
113 citations
••
TL;DR: In this paper, an integrated assessment of greenhouse gas emissions in slash and burn agriculture and an alternative chop-and-mulch system in the Amazon Basin is presented. And the authors demonstrate a potential 'win-win' strategy for maintaining soil fertility and reducing net greenhouse gases emissions, thus simultaneously contributing to sustainability at both spatial scales.
Abstract: Fires set for slash-and-burn agriculture contribute to the current unsustainable accumulation of atmospheric greenhouse gases, and they also deplete the soil of essential nutrients, which compromises agricultural sustainability at local scales. Integrated assessments of greenhouse gas emissions have compared intensive cropping systems in industrialized countries, but such assessments have not been applied to common cropping systems of smallholder farmers in developing countries. We report an integrated assessment of greenhouse gas emissions in slash-and-bum agriculture and an alternative chop-and-mulch system in the Amazon Basin. The soil consumed atmospheric methane (CH 4 ) under slash-and-burn treatment and became a net emitter of CH 4 to the atmosphere under the mulch treatment. Mulching also caused about a 50% increase in soil emissions of nitric oxide and nitrous oxide and required greater use of fertilizer and fuel for farm machinery. Despite these significantly higher emissions of greenhouse gases during the cropping phase under the alternative chop-and-mulch system, calculated pyrogenic emissions in the slash-and-burn system were much larger, especially for CH 4 . The global warming potential CO 2 -equivalent emissions calculated for the entire crop cycles were at least five times lower in chop-and-mulch compared with slash-and-bum. The crop yields were similar for the two systems. While economic and logistical considerations remain to be worked out for alternatives to slash-and-bum, these results demonstrate a potential 'win-win' strategy for maintaining soil fertility and reducing net greenhouse gas emissions, thus simultaneously contributing to sustainability at both spatial scales.
113 citations