Showing papers on "Atmospheric methane published in 2000"
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TL;DR: The most promising areas for future research for reducing methanogenesis are the development of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors in theRumen and reduction in protozoal numbers in the rumen.
Abstract: The aim of this paper is to review the role of methane in the global warming scenario and to examine the contribution to atmospheric methane made by enteric fermentation, mainly by ruminants. Agricultural emissions of methane in the EU-15 have recently been estimated at 10.2 million tonnes per year and represent the greatest source. Of these, approximately two-thirds come from enteric fermentation and one-third from livestock manure. Fermentation of feeds in the rumen is the largest source of methane from enteric fermentation and this paper considers in detail the reasons for, and the consequences of, the fact that the molar percentage of the different volatile fatty acids produced during fermentation influences the production of methane in the rumen. Acetate and butyrate promote methane production while propionate formation can be considered as a competitive pathway for hydrogen use in the rumen. The many alternative approaches to reducing methane are considered, both in terms of reduction per animal and reduction per unit of animal product. It was concluded that the most promising areas for future research for reducing methanogenesis are the development of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors in the rumen and reduction in protozoal numbers in the rumen. It is also stressed that the reason ruminants are so important to mankind is that much of the world's biomass is rich in fibre. They can convert this into high quality protein sources (i.e. meat and milk) for human consumption and this will need to be balanced against the concomitant production of methane.
1,172 citations
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TL;DR: Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials.
Abstract: Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials. Furthermore, several large, brief, negative excursions (up to -6 per mil) coinciding with smaller shifts (up to -3 per mil) in depth-stratified planktonic foraminiferal species indicate massive releases of methane from basin sediments. Gas hydrate stability was modulated by intermediate-water temperature changes induced by switches in thermohaline circulation. These oscillations were likely widespread along the California margin and elsewhere, affecting gas hydrate instability and contributing to millennial-scale atmospheric methane oscillations.
552 citations
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TL;DR: It is found that a CH4 mixing ratio of 10(-4) (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.3-2.4 Ga, which could have triggered the Earth's first widespread glaciation.
Abstract: Earth appears to have been warm during its early history despite the faintness of the young Sun. Greenhouse warming by gaseous CO 2 and H 2 O by itself is in conflict with constraints on atmospheric CO 2 levels derived from paleosols for early Earth. Here we explore whether greenhouse warming by methane could have been important. We find that a CH 4 mixing ratio of 10 -4 (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.8 Ga. Such a CH 4 concentration could have been readily maintained by methanogenic bacteria, which are thought to have been an important component of the biota at that time. Elimination of the methane component of the greenhouse by oxidation of the atmosphere at about 2.3 - 2.4 Ga could have triggered the Earth's first widespread glaciation.
530 citations
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TL;DR: It is shown here that the activity and growth of such bacteria in the root zone of rice plants are stimulated after fertilization, and the bacteria responsible for this effect are identified using a combination of radioactive fingerprinting and molecular biology techniques.
Abstract: Methane is involved in a number of chemical and physical processes in the Earth's atmosphere, including global warming. Atmospheric methane originates mainly from biogenic sources, such as rice paddies and natural wetlands; the former account for at least 30% of the global annual emission of methane to the atmosphere. As an increase of rice production by 60% is the most appropriate way to sustain the estimated increase of the human population during the next three decades, intensified global fertilizer application will be necessary: but it is known that an increase of the commonly used ammonium-based fertilizers can enhance methane emission from rice agriculture. Approximately 10-30% of the methane produced by methanogens in rice paddies is consumed by methane-oxidizing bacteria associated with the roots of rice; these bacteria are generally thought to be inhibited by ammonium-based fertilizers, as was demonstrated for soils and sediments. In contrast, we show here that the activity and growth of such bacteria in the root zone of rice plants are stimulated after fertilization. Using a combination of radioactive fingerprinting and molecular biology techniques, we identify the bacteria responsible for this effect. We expect that our results will make necessary a re-evaluation of the link between fertilizer use and methane emissions, with effects on global warming studies.
468 citations
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TL;DR: This review presents the current knowledge about the highly complex microbiology of flooded rice paddies and describes the predominant microbial groups and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea.
Abstract: Flooded rice paddies are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the ‘greenhouse’ effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure, and dynamics of microbial communities as well as structure–function relationships between microbial groups. Flooded rice paddy soil can be considered as a system with three compartments (oxic surface soil, anoxic bulk soil, and rhizosphere) characterized by different physio-chemical conditions. After flooding, oxygen is rapidly depleted in the bulk soil. Anaerobic microorganisms, such as fermentative bacteria and methanogenic archaea, predominate within the microbial community, and thus methane is the final product of anaerobic degradation of organic matter. In the surface soil and the rhizosphere well-defined microscale chemical gradients can be measured. The oxygen profile seems to govern gradients of other electron acceptors (e.g., nitrate, iron(III), and sulfate) and reduced compounds (e.g., ammonium, iron(II), and sulfide). These gradients provide information about the activity and spatial distribution of functional groups of microorganisms. This review presents the current knowledge about the highly complex microbiology of flooded rice paddies. In Section 2 we describe the predominant microbial groups and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea. Section 3 describes the spatial and temporal development of microscale chemical gradients measured in experimentally defined model systems, including gradients of oxygen and dissolved and solid-phase iron(III) and iron(II). In Section 4, the results of measurements of microscale gradients of oxygen, pH, nitrate–nitrite, and methane in natural rice fields and natural rice soil cores taken to the laboratory will be presented. Finally, perspectives of future research are discussed (Section 5).
447 citations
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TL;DR: In this paper, the authors report the range and statistical distribution of oxidation rates of atmospheric CH4 in soils found in Northern Europe in an international study, and compares them with published data for various other ecosystems.
Abstract: This paper reports the range and statistical distribution of oxidation rates of atmospheric CH4 in soils found in Northern Europe in an international study, and compares them with published data for various other ecosystems. It reassesses the size, and the uncertainty in, the global terrestrial CH4 sink, and examines the effect of land-use change and other factors on the oxidation rate.
Only soils with a very high water table were sources of CH4; all others were sinks. Oxidation rates varied from 1 to nearly 200 μg CH4 m−2 h−1; annual rates for sites measured for ≥1 y were 0.1–9.1 kg CH4 ha−1 y−1, with a log-normal distribution (log-mean ≈ 1.6 kg CH4 ha−1 y−1). Conversion of natural soils to agriculture reduced oxidation rates by two-thirds –- closely similar to results reported for other regions. N inputs also decreased oxidation rates. Full recovery of rates after these disturbances takes > 100 y. Soil bulk density, water content and gas diffusivity had major impacts on oxidation rates. Trends were similar to those derived from other published work. Increasing acidity reduced oxidation, partially but not wholly explained by poor diffusion through litter layers which did not themselves contribute to the oxidation. The effect of temperature was small, attributed to substrate limitation and low atmospheric concentration.
Analysis of all available data for CH4 oxidation rates in situ showed similar log-normal distributions to those obtained for our results, with generally little difference between different natural ecosystems, or between short-and longer-term studies. The overall global terrestrial sink was estimated at 29 Tg CH4 y−1, close to the current IPCC assessment, but with a much wider uncertainty range (7 to > 100 Tg CH4 y−1). Little or no information is available for many major ecosystems; these should receive high priority in future research.
440 citations
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TL;DR: In this article, the authors present high resolution records of atmospheric methane from the GISP2 (Greenland Ice Sheet Project 2) ice core for four rapid climate transitions that occurred during the past 50 ka.
Abstract: We present high resolution records of atmospheric methane from the GISP2 (Greenland Ice Sheet Project 2) ice core for four rapid climate transitions that occurred during the past 50 ka: the end of the Younger Dryas at 11.8 ka, the beginning of the Bolling-Allerod period at 14.8 ka, the beginning of interstadial 8 at 38.2 ka, and the beginning of interstadial 12 at 45.5 ka. During these events, atmospheric methane concentrations increased by 200–300 ppb over time periods of 100–300 years, significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record. We suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change. We find no evidence for rapid, massive methane emissions that might be associated with large-scale decomposition of methane hydrates in sediments. With additional results from the Taylor Dome Ice Core (Antarctica) we also reconstruct changes in the interpolar methane gradient (an indicator of the geographical distribution of methane sources) associated with some of the rapid changes in atmospheric methane. The results indicate that the rise in methane at the beginning of the Bolling-Allerod period and the later rise at the end of the Younger Dryas were driven by increases in both tropical and boreal methane sources. During the Younger Dryas (a 1.3 ka cold period during the last deglaciation) the relative contribution from boreal sources was reduced relative to the early and middle Holocene periods.
308 citations
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TL;DR: In this paper, stable carbon isotopic analyses of organic carbon (δ 13 C) in individual paleosol profiles from Permian-Triassic sequences of Antarctica reveal systematic isotopic variations with profile depth.
Abstract: Stable carbon isotopic analyses of organic carbon (δ 13 C) in individual paleosol profiles from Permian–Triassic sequences of Antarctica reveal systematic isotopic variations with profile depth. These variations are in many cases analogous to those in modern soils, which are functions of redox conditions, soil development, and degree and type of microbial decay. In modern soils, these isotopic depth functions develop independently from vegetation changes (C 3 versus C 4 vegetation) and can be diagnostic of soil orders. This study shows that soil-intrinsic functions can be preserved in the δ 13 C values of paleosols as old as 260 Ma and constitute valuable data for paleoecological interpretations. A large carbon isotopic offset of as much as 10‰ in whole paleosol profiles across the Permian-Triassic boundary indicates significant changes in the soil biogeochemistry and the soil-atmosphere system. Early Triassic paleosols are distinctive in their extremely low δ 13 C values (to −42‰) and often show an anomalous δ 13 C depth distribution compared to both Permian paleosols and modern soils. Highly depleted δ 13 C values, as the ones in Early Triassic paleosols, are suggested to be associated with microbial methane oxidation (methanotrophy). This hypothesis implies increased methane concentrations in the Early Triassic soil-atmosphere system. Increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the Permian–Triassic boundary.
265 citations
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TL;DR: Analysis of labelled phospholipid fatty acids provided unambiguous evidence of methane assimilation at true atmospheric concentrations, and high proportions of 13C-labelled C18 fatty acids and the co-occurrence of a labelled, branched C17 fatty acid indicated that a new methanotroph was the predominant soil micro-organism responsible for atmospheric methane oxidation.
Abstract: Well-drained non-agricultural soils mediate the oxidation of methane directly from the atmosphere, contributing 5 to 10% towards the global methane sink1,2. Studies of methane oxidation kinetics in soil infer the activity of two methanotrophic populations: one that is only active at high methane concentrations (low affinity) and another that tolerates atmospheric levels of methane (high affinity). The activity of the latter has not been demonstrated by cultured laboratory strains of methanotrophs, leaving the microbiology of methane oxidation at atmospheric concentrations unclear3,4. Here we describe a new pulse-chase experiment using long-term enrichment with 12CH4 followed by short-term exposure to 13CH4 to isotopically label methanotrophs in a soil from a temperate forest. Analysis of labelled phospholipid fatty acids (PLFAs) provided unambiguous evidence of methane assimilation at true atmospheric concentrations (1.8–3.6 p.p.m.v.). High proportions of 13C-labelled C18 fatty acids and the co-occurrence of a labelled, branched C17 fatty acid indicated that a new methanotroph, similar at the PLFA level to known type II methanotrophs, was the predominant soil micro-organism responsible for atmospheric methane oxidation.
232 citations
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TL;DR: It seems, however, that extra ammonium may stimulate soil bacteria that oxidize methane, and so reduce emissions.
Abstract: Rice agriculture is projected to expand by up to 70% over the next 25 years, and is likely to mean much more intensive use of ammonium-based nitrogen fertilizers. That is a worry because rice paddies are one of the main sources of methane (a greenhouse gas) in the atmosphere, and increased emissions would be undesirable. It seems, however, that extra ammonium may stimulate soil bacteria that oxidize methane, and so reduce emissions.
195 citations
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TL;DR: In this article, the authors assessed the impact of different levels of urea and HPO4 on the microbial processes involved in production and consumption of CH4 in rice field soil.
Abstract: The emission of the greenhouse gas CH4 from rice paddies is strongly influenced by management practices such as the input of ammonium-based fertilisers. We assessed the impact of different levels (200 and 400 kgN.ha(-1)) of urea and (NH4)(2)HPO4 on the microbial processes involved in production and consumption of CH4 in rice field soil. We used compartmented microcosms which received fertiliser twice weekly. Potential CH4 production rates were substantially higher in the rice rhizosphere than in unrooted soil, but were not affected by fertilisation. However, CH4 emission was reduced by the addition of fertiliser and was negatively correlated with pore water NH4+ concentration, probably as the consequence of elevated CH4 oxidation due to fertilisation. CH4 oxidation as well as numbers of methanotrophs was distinctly stimulated by the addition of fertiliser and by the presence of the rice plant. Without fertiliser addition, nitrogen- limitation of the methanotrophs will restrict the consumption of CH4. This may have a major impact on the global CH4 budget, as nitrogen-limiting conditions will be the normal situation in the rice rhizosphere. Elevated potential nitrifying activities and numbers were only detected in microcosms fertilised with urea. However, a substantial part of the nitrification potential in the rhizosphere of rice was attributed to the activity of methanotrophs, as was demonstrated using the inhibitors CH3F and C2H2. [KEYWORDS: fertiliser; methane emission; methane oxidation; microcosm; rice Atmospheric methane; oxidizing bacteria; ch4 oxidation; nitrous-oxide; flooded rice; sparganium-eurycarpum; nitrosococcus-oceanus; nitrosomonas-europaea; water management; glyceria-maxima]
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01 Jan 2000
TL;DR: The record of Atmospheric Methane and its sources is described in this paper, where the authors use stable isotopes and global budgets to constrain atmospheric Methane Budgets and to limit Methane production.
Abstract: 1 Atmospheric Methane: An Introduction.- Record of Atmospheric Methane.- 2 The Ice Core Record of Atmospheric Methane.- 3 The Isotopic Composition of Atmospheric Methane and Its Sources.- Formation and Consumption of Methane.- 4 Biological Formation and Consumption of Methane.- Sources and Sinks.- 5 Can Stable Isotopes and Global Budgets Be Used to Constrain Atmospheric Methane Budgets?.- 6 Methane Sinks, Distributions, and Trends.- 7 Sources of Methane: An Overview.- Methane Emissions from Individual Sources.- 8 Ruminants and Other Animals.- 9 Rice Agriculture: Factors Controlling Emissions.- 10 Rice Agriculture: Emissions.- 11 Biomass Burning.- 12 Wetlands.- 13 Waste Management.- 14 Fossil Fuel Industries.- 15 Geological Sources of Methane.- The Environmental Role of Methane and Current Issues.- 16 Methane in the Global Environment.
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TL;DR: In this paper, four sandy soils with different organic matter content (1-9% w/w) from two landfills in Denmark were investigated in batch experiments in the laboratory to determine the response of methane oxidation at low temperatures and different soil moisture regimes.
Abstract: Soil exposed to elevated methane concentrations can develop a high capacity for methane oxidation. Methane oxidation at high and low methane concentrations is performed by different types of methanotrops and therefore oxidation rates found at low temperatures at the atmospheric methane content cannot be extrapolated to soils exposed to high methane concentrations. Four sandy soils with different organic matter content (1-9% w/w) from two landfills in Denmark were investigated in batch experiments in the laboratory to determine the response of methane oxidation at low temperatures and different soil moisture regimes. At 2°C the methane oxidation rates were 0.005 to 0.17 μmol g -1 h -1 , and calculations showed that it was possible to oxidize all the produced methane at older landfills, even during the winter. Therefore, methane oxidation in top covers of landfills is an alternative to gas recovery at smaller and older landfills in northern Europe. Equations have been developed that describe the dependency of temperature and soil moisture content for each soil. The oxidation rates depended significantly on the soils (and thereby organic matter content), temperature, and soil moisture content. Soil moisture was the most important factor. However, high Q 10 values indicate that temperature also was important. The four soils tested had optimum soil moisture content between 11 and 32%. At increasing organic matter content, both the optimal soil moisture content and the maximum oxidation rate increased.
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TL;DR: In this article, the authors used a three-dimensional chemistry-transport model to estimate the source strength of preindustrial CH4 from natural wetlands, with an estimated ± 2σ uncertainty range of 130-194 Tg(CH4) yr−1.
Abstract: Previous attempts to quantify the global source strength of CH4 from natural wetlands have resulted in a range of 90–260 Tg(CH4) yr−1. This relatively uncertain estimate significantly limits our understanding of atmospheric methane. In this study we reduce this uncertainty by simulating preindustrial CH4 with a three-dimensional chemistry-transport model. Methane mixing ratios and δ13C-CH4, as deduced from ice cores, and estimates of other preindustrial sources and sinks, are used as constraints. This yields an average preindustrial natural wetland source strength of 163 Tg(CH4) yr−1, with an estimated ±2σ uncertainty range of 130–194 Tg(CH4) yr−1. The present natural wetland source may be ∼10% smaller, owing to drainage and cultivation of wetland area since 1800 A.D. The simulated pole-to-pole concentration difference is found to be rather insensitive to the assumed relative contributions of important preindustrial sources and sinks, and therefore imposes only a limited constraint on the estimate of natural wetland emissions. In contrast, δ13C-CH4 could provide robust constraints, but, unfortunately, at present reliable measurements are absent. Estimates of the historic development of anthropogenic CH4 sources, in combination with our model calculations, can largely explain the increase of methane mixing ratios during the nineteenth century. Results for the twentieth century indicate that these historical emission inventories underestimate anthropogenic emissions by at least 10%. Simulations of preindustrial and present-day isotopic ratios show that the growth of anthropogenic sources since 1800 A.D. may have increased δ13C-CH4 by 3‰.
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TL;DR: In this article, the hydrogen and carbon kinetic isotope effects (KJEs) occurring during uptake of atmospheric methane (CH4) by soils were measured using in situ static flux chambers in a native grassland and a temperate forest in Washington State.
Abstract: The hydrogen and carbon kinetic isotope effects (KJEs) occurring during uptake of atmospheric methane (CH4) by soils were measured using in situ static flux chambers in a native grassland and a temperate forest in Washington State. The hydrogen KIE was αDsoil =k(CH4)/k(CH3D) = 1.099 ± 0.030 and 1.066 ± 0.007 for the grassland and forest, respectively. The carbon KIE of αCsoil =k(12CH4)/k(13CH4) = 1.0173 ± 0.0010 and 1.0181 ± 0.0004 for the grassland and forest, respectively, compares well to previous determinations in other ecosystems. Local spatial variability in αsoil was as large as the between-ecosystem variability. The dependence of αsoil on αox and the KIE during diffusion is described. The apparent KIE associated with microbial oxidation, αox, was determined from αsoil and the relative rates of CH4 oxidation and diffusion in the soil column, derived from observed steady state profiles of soil air CH4 concentration. The apparent αox ranged from 1.094 to 1.209 for αDox and from 1.0121 to 1.0183 for αCox. These are the first determinations of the hydrogen KIEs during soil uptake of atmospheric CH4 and during aerobic microbial oxidation of CH4 at or below atmospheric concentrations. The KIE during uptake of atmospheric CH4 by soils is significantly different than the KIEs associated with the other sinks of atmospheric CH4. The interhemispheric asymmetry in the strength of the soil sink of atmospheric CH4 suggests a difference of ∼6‰ between the overall hydrogen KIEs in the two hemispheres. Modeling studies of the global atmospheric CH4 budget using deuterium as a tracer must therefore include αDsoil.
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TL;DR: In this paper, the authors use a simple model simulation incorporating a plausible scenario of the global methane source history over 1700-2010, which includes an unchanged source since 1990, to assess their likely magnitudes in the global atmosphere over recent decades.
Abstract: A recent paper by Tans [1997] has drawn attention to the isotopic disequilibrium that inevitably prevails when atmospheric methane is not in steady state with its sources, noting in particular the very slow adjustment of the isotopic signature δ13C toward its steady state. Our aim in this paper is to clarify the nature of disequilibrium effects on δ13C(CH4) and to assess their likely magnitudes in the global atmosphere over recent decades. We use a simple model simulation incorporating a plausible scenario of the global methane source history over 1700–2010, which includes an unchanged source since 1990. The simulation of both mixing ratio and δ13C compare favorably with the secular features of a 10-year data set (1988–1998) from Baring Head, New Zealand, and of a 17-year data set (1978–1995) in air archived from Cape Grim, Australia. This corroborates a recent analysis of those data sets and their compatibility with stabilized sources. We show that the slow adjustment of δ13C toward steady state arises from the effect of isotope fractionation on the cancellation of contributing terms to δ13C. We explore the implications of disequilibrium for the usual practice of relating δ13C values in the atmosphere to those in the aggregate source through a shift induced by fractionation and quantify the flaws in this practice. Finally, we examine the sensitivity of the atmospheric secular response, in both mixing ratio and δ13C, to sustained changes in source and sink and show that δ13C is a potentially powerful diagnostic of such changes.
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TL;DR: In this paper, the seasonal fluctuation in CH 4 fluxes from water bodies and the difference in the methane efflux from vegetated and unvegetated surfaces of natural and man-made water bodies as well as investigate the edaphic factors controlling the methane production and emission.
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TL;DR: In this paper, continuous measurements from 1990 to 1998 of atmospheric CH 4 from the Canadian observational sites at Fraserdale (49°53'N 81°34'W) and Alert (82°27'N 62°31'W), were used to estimate CH 4 emissions from the Hudson Bay Lowland (HBL), a 320,000 km 2 semicontinuous wetland region in central Canada.
Abstract: Wetlands are an important source of atmospheric methane (CH 4 ), but the strength of this source and its sensitivity to potential changes in climate are still uncertain. In this study, continuous measurements from 1990 to 1998 of atmospheric CH 4 from the Canadian observational sites at Fraserdale (49°53'N 81°34'W) and Alert (82°27'N 62°31'W) are used to estimate CH 4 emissions from the Hudson Bay Lowland (HBL), a 320,000 km 2 semicontinuous wetland region in central Canada. The HBL comprises ∼ 10% of the total area of northern wetlands. A conceptually simple approach was used to calculate the methane emission flux using the CH 4 concentration difference between Alert and Fraserdale, the residence time of the air mass over the HBL, and the mixing height of the convective boundary layer. Emission rates estimated using this approach for 1990 compare well with empirical aircraft and tower flux measurements made within the HBL during the same time period, thus indicating that the methodology used is reasonable. Annual CH 4 emission rates range from 0.23 to 0.50 Tg CH 4 yr -1 and are much lower than many empirical flux measurements observed at other northern wetland sites. A seasonal temperature sensitivity with a Q 10 of about 4 was found. Moreover, the observed interannual variations in emissions are well correlated to variations in annual air temperatures corresponding to a sensitivity of Q 10 7. That is, a 10°C change in annual temperature would result in a sevenfold change in wetland emissions which is much larger than Q 10 values used in current global CH 4 models (typically Q 10 1.5). Our findings suggest that northern wetland emissions are probably overestimated to date but may increase significantly due to predicted global warming.
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TL;DR: Titan's atmospheric methane appears to have been formed from carbon and other carbon compounds, either by gas phase reactions in the subnebula or by accretional heating during the formation of Titan.
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TL;DR: In this article, the authors investigated the effect of combustion efficiency on the amount of methane released by combustion in controlled forest and grassland burns and within a wood stove, and found that the proportion of methane produced in these fires varied from 0.2 to 8.5% of the carbon dioxide production.
Abstract: Factors controlling the δ13C of methane released by combustion include the combustion efficiency of the fire and the δ13C of the fuel. Smoldering fires produced 13C-depleted methane relative to hot, flaming fires in controlled forest and grassland burns and within a wood stove. Pine forest burns in the southeastern United States produced methane which ranged from −21 to −30‰, while African grassland burns varied from −17 to −26‰, depending upon combustion phase. African woodland burns produced methane at −30‰. In forest burns in the southeastern United States, the δ13C of methane released with smoldering was significantly 13C depleted relative to methane released under hot flaming conditions. Methane released with smoldering was depleted by 2–3‰ relative to the fuel δ13C, but this difference was not significant. The δ13C of methane produced in a variety of wood stove conditions varied from −9 to −25‰ and also depended upon combustion efficiency. Similar results were found for methane produced by gasoline automobile engines, where the δ13C of methane varied from −9 to −22‰. For combustion occurring within the confining chamber of a wood stove or engine the δ13C of methane was clearly 13C enriched relative to the δ13C of the fuel, possibly because of preferential combustion of 12CH4 in the gas phase. Significant quantities of ethylene (up to 25 to 50% of methane concentrations) were produced in southeastern U.S. forest fires, which may have consequences for physiological and reproductive responses of plants in the ecosystem. Methane production in these fires varied from 0.2 to 8.5% of the carbon dioxide production.
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01 Jan 2000TL;DR: In this article, the authors describe the progress towards the understanding of global budgets and trends of global methane and provide a guide to the book, and describe briefly the progress toward understanding the global budget and trends.
Abstract: Methane is a greenhouse gas thought to be second only to CO2 as an agent of future global warming. The increasing trend is the single most important reason for the current interest in methane It is the foundation for much of the research on methane during the past decade, particularly on the global budget, which is tied directly to explaining why it is increasing. Figure 1 (a-f) shows the concentration and trends of methane over the recent decades and back to a thousand years. I want to describe briefly the progress towards the understanding of global budgets and trends, and to provide a guide to the book.
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TL;DR: In this paper, the authors quantify the methane exchange processes on a regional scale in the Ruhr Basin and the Lower Rhine Embayment and show that methane release by upcast mining shafts dominates the methane consumption by bacterial oxidation in the soils.
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01 Jan 2000TL;DR: In this paper, the authors consider geological sources of methane, and natural pathways which enable it to enter the atmosphere, and make reference to releases associated with geological resource extraction, however the most significant of these (coal and petroleum) are discussed in specific chapters elsewhere in this volume.
Abstract: Methane is one of many gases produced by geological processes. Others include: CO2, H2, H2S, N2, SO2, H2O (as steam or water vapour), and the petroleum gases (ethane, propane, butane and pentane). This chapter considers geological sources of methane, and natural pathways which enable it to enter the atmosphere. For the purposes of this chapter ‘geological’ sources are taken to include sediments of all ages: ancient and modern, including those being actively deposited at the present day. Reference is also made to releases associated with geological resource extraction, however the most significant of these (coal and petroleum) are discussed in specific chapters elsewhere in this volume.
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01 Jan 2000TL;DR: In the last 200 years, anthropogenic activities such as rice cultivation, animal production, fossil fuel burning and waste management have resulted in a dramatic increase of the atmospheric CH4 concentration during the last 20 years.
Abstract: Methane is a greenhouse gas contributing about 19% to the enhanced greenhouse effect (IPCC, 1994). Anthropogenic activities, such as rice cultivation, animal production, fossil fuel burning and waste management have resulted in a dramatic increase of the atmospheric CH4 concentration during the last 200 years. Its actual concentration is 1.72 ppmv, currently increasing at a rate of 0.6–0.8% per year (Houghton et al.,1996).
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TL;DR: The results suggest that widespread acidification of soils and aluminum mobilization due to acid precipitation may exacerbate inhibition of atmospheric methane consumption due to changes in other parameters and increase the contribution of methane to global warming.
Abstract: Atmospheric methane consumption by Maine forest soils was inhibited by additions of environmentally relevant levels of aluminum. Aluminum chloride was more inhibitory than nitrate or sulfate salts, but its effect was comparable to that of a chelated form of aluminum. Inhibition could be explained in part by the lower soil pH values which resulted from aluminum addition. However, significantly greater inhibition by aluminum than by mineral acids at equivalent soil pH values indicated that inhibition also resulted from direct effects of aluminum per se. The extent of inhibition by exogenous aluminum increased with increasing methane concentration for soils incubated in vitro. At methane concentrations of >10 ppm, inhibition could be observed when aluminum chloride was added at concentrations as low as 10 nmol g (fresh weight) of soil−1. These results suggest that widespread acidification of soils and aluminum mobilization due to acid precipitation may exacerbate inhibition of atmospheric methane consumption due to changes in other parameters and increase the contribution of methane to global warming.
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TL;DR: In this article, field plots of aspen and black spruce in the Alaskan boreal forest were fertilized repeatedly with nitrogen during the 1993 summer growing season, and weekly determinations of the influence of fertilization on atmospheric CH4 oxidation were made with static chambers.
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01 Jan 2000TL;DR: In this article, the authors examined past trends in the concentration of methane, the sources and sinks affecting its growth rate, and the factors that could affect its growth in the future, and examined the current understanding of the effects of methane on atmospheric chemistry and climate.
Abstract: The concentration of methane (CH4), the most abundant organic trace gas in the atmosphere, has increased dramatically over the last few centuries, more than doubling its concentration. Increasing concentrations of methane are of special concern because of their effects on climate and atmospheric chemistry. On a per molecule basis, additional methane is much more effective as a greenhouse gas than additional CO2. Methane is also important to both tropospheric and stratospheric chemistry. Here, we examine past trends in the concentration of methane, the sources and sinks affecting its growth rate, and the factors that could affect its growth rate in the future. This study also examines the current understanding of the effects of methane on atmospheric chemistry and climate.
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01 Jan 2000TL;DR: In this paper, the authors present a global coverage of atmospheric methane latitudinal variation and provide an overview of the source strengths and sources of fluxes of methane across the geosphere-biosphere-atmosphere interface.
Abstract: Global climate change associated with the increasing atmospheric methane burden is an important societal concern. Today we can monitor with good precision the yearly 1% rise in lower tropospheric methane mixing ratios (e.g., Blake and Rowland, 1988), and we have adequate, basic global coverage of atmospheric methane latitudinal variation. Mesoscopically, we are able to roughly estimate the various source strengths, e.g., from wetlands, agriculture, fossil fuels, but there is considerable uncertainty in the actual magnitudes of the various individual fluxes of methane across the geosphere-biosphere-atmosphere interface. This knowledge deficit includes our understanding of both release and uptake process-groups. Control of methane emissions to the atmosphere requires that we reliably characterize these source-sink relationships.
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TL;DR: In this paper, the authors measured methane consumption in Swedish forest soil once every autumn for 2 years after fertilization with 150 kg N −1 as calcium ammonium-nitrate, and found that the methane oxidation capacity was substantially higher in the fertilized plots compared with the controls.