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Showing papers on "Atmospheric methane published in 2010"


Journal ArticleDOI
05 Mar 2010-Science
TL;DR: It is shown that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere, and that the current atmospheric venting flux is on par with previous estimates of methane venting from the entire World Ocean.
Abstract: Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere. The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate.

521 citations


Journal ArticleDOI
TL;DR: In this article, an important question is to what extent increased temperatures will affect the performance of methane formation (MF) and methane oxidation (MO) rates in aquatic environments, and the answer is that it depends on methane formation and MO rates.
Abstract: Methane emissions from aquatic environments depend on methane formation (MF) and methane oxidation (MO) rates. One important question is to what extent increased temperatures will affect the balanc ...

244 citations


Journal ArticleDOI
TL;DR: A review of the available scientific literature on how natural sources and the atmospheric fate of methane may be affected by future climate change is presented in this paper, where the authors discuss how processes governing methane wetland emissions, permafrost thawing, and destabilization of marine hydrates may affect the climate system.
Abstract: We have reviewed the available scientific literature on how natural sources and the atmospheric fate of methane may be affected by future climate change. We discuss how processes governing methane wetland emissions, permafrost thawing, and destabilization of marine hydrates may affect the climate system. It is likely that methane wetland emissions will increase over the next century. Uncertainties arise from the temperature dependence of emissions and changes in the geographical distribution of wetland areas. Another major concern is the possible degradation or thaw of terrestrial permafrost due to climate change. The amount of carbon stored in permafrost, the rate at which it will thaw, and the ratio of methane to carbon dioxide emissions upon decomposition form the main uncertainties. Large amounts of methane are also stored in marine hydrates, and they could be responsible for large emissions in the future. The time scales for destabilization of marine hydrates are not well understood and are likely to be very long for hydrates found in deep sediments but much shorter for hydrates below shallow waters, such as in the Arctic Ocean. Uncertainties are dominated by the sizes and locations of the methane hydrate inventories, the time scales associated with heat penetration in the ocean and sediments, and the fate of methane released in the seawater. Overall, uncertainties are large, and it is difficult to be conclusive about the time scales and magnitudes of methane feedbacks, but significant increases in methane emissions are likely, and catastrophic emissions cannot be ruled out. We also identify gaps in our scientific knowledge and make recommendations for future research and development in the context of Earth system modeling.

239 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that methylated compounds may serve as precursors for methane and thermodynamic calculations show that methylotrophic methanogenesis can provide energy in aerobic environments.
Abstract: . A methane surplus relative to the atmospheric equilibrium is a frequently observed feature of ocean surface water. Despite the common fact that biological processes are responsible for its origin, the formation of methane in aerobic surface water is still poorly understood. We report on methane production in the central Arctic Ocean, which was exclusively detected in Pacific derived water but not nearby in Atlantic derived water. The two water masses are distinguished by their different nitrate to phosphate ratios. We show that methane production occurs if nitrate is depleted but phosphate is available as a P source. Apparently the low N:P ratio enhances the ability of bacteria to compete for phosphate while the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) is utilized as a C source. This was verified by experimentally induced methane production in DMSP spiked Arctic sea water. Accordingly we propose that methylated compounds may serve as precursors for methane and thermodynamic calculations show that methylotrophic methanogenesis can provide energy in aerobic environments.

194 citations


Journal ArticleDOI
TL;DR: In this article, the role of varying wetland area on the seasonal and interannual variability of CH4 wetland emissions over the past decade was provided over the period 1993-2000 by a suite of satellite observations from multiple sensors.
Abstract: [1] Climate variability impacts CH4 wetland sources as changes in flux density per unit area and via expansion or contraction of wetland areas in response to surface hydrological processes This paper is a first attempt to isolate the role of varying wetland area on the seasonal and interannual variability of CH4 wetland emissions over the past decade Wetland area extent at monthly intervals was provided over the period 1993–2000 by a suite of satellite observations from multiple sensors The regionally variable fraction of wetland area was optimized using satellite observations of flooded area as a first estimate and further adjusted to match the seasonal cycle of CH4 fluxes retrieved from a global atmospheric inversion Wetland flux densities of CH4 were calculated by coupling the ORCHIDEE global vegetation model with a process-based wetland CH4 emission model, calibrated by optimizing its parameters at the site level against representative CH4 flux time series For boreal bogs north of 50°N, we found that variations in area contributed about 30% to the annual flux For temperate and tropical wetlands, the variations in area has almost no influence on the annual CH4 emissions but contributes significantly to the seasonal behavior, accounting for 40% and 66% of the seasonal amplitude of fluxes, respectively In contrast, the interannual variability of wetland area appears to be the dominant cause of interannual variations in regional CH4 emissions from wetlands at all latitudes (largest in the tropics), with up to 90% of annual flux anomalies explained by wetland area anomalies in some years For example, in 1998, boreal wetlands north of 50°N contributed to approximately 80% of the positive anomaly according to our calculations We also found that climate anomalies can lead to both increased emitting areas and decreased flux densities at the same time, with opposite effects on the total CH4 flux entering the atmosphere With a view to forecasting the future trajectory of atmospheric methane content, our results point to the absolute necessity to be able to predict the variations in wetland extent, a hydrological problem, in order to affirm the reliability of simulations of changing methane emissions perturbed by climate

157 citations


Journal ArticleDOI
TL;DR: It is indicated that the methanotrophic diversity and abundance in spruce soils are lower than those of beech soils, suggesting that tree species-related factors might influence the in situ activity of methnotrophs.
Abstract: Norway spruce (Picea abies) forests exhibit lower annual atmospheric methane consumption rates than do European beech (Fagus sylvatica) forests. In the current study, pmoA (encoding a subunit of membrane-bound CH4 monooxygenase) genes from three temperate forest ecosystems with both beech and spruce stands were analyzed to assess the potential effect of tree species on methanotrophic communities. A pmoA sequence difference of 7% at the derived protein level correlated with the species-level distance cutoff value of 3% based on the 16S rRNA gene. Applying this distance cutoff, higher numbers of species-level pmoA genotypes were detected in beech than in spruce soil samples, all affiliating with upland soil cluster α (USCα). Additionally, two deep-branching genotypes (named 6 and 7) were present in various soil samples not affiliating with pmoA or amoA. Abundance of USCα pmoA genes was higher in beech soils and reached up to (1.2 ± 0.2) × 108pmoA genes per g of dry weight. Calculated atmospheric methane oxidation rates per cell yielded the same trend. However, these values were below the theoretical threshold necessary for facilitating cell maintenance, suggesting that USCα species might require alternative carbon or energy sources to thrive in forest soils. These collective results indicate that the methanotrophic diversity and abundance in spruce soils are lower than those of beech soils, suggesting that tree species-related factors might influence the in situ activity of methanotrophs.

136 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the most extensive lateral expansion of high-latitude peatlands occurred only after 5-ka, parallel with the rise of CH 4 in the ice cores.

121 citations


Journal ArticleDOI
TL;DR: In this article, an up-scaling of the PEATLAND-VU emission model to the global scale with a spatial resolution of 0.5 degrees for the period 2001-2006 is presented.
Abstract: Methane (CH4) emission from boreal, arctic and subarctic wetlands constitutes a potentially positive feedback to global climate warming. Many process-based models have been developed, but high uncertainties remain in estimating the amount of CH4 released from wetlands at the global scale. This study tries to improve estimates of CH4 emissions by up-scaling a wetland CH4 emission model, PEATLAND-VU, to the global scale with a spatial resolution of 0.5 degrees for the period 2001-2006. This up-scaling was based on the global circum-arctic distribution of wetlands with hydrological conditions being specified by a global hydrological model, PCR-GLOBWB. In addition to the daily hydrological output from PCR-GLOBWB, comprising water table depths and snow thickness, the parameterization included air temperature as obtained from the ECMWF Operational Archive. To establish the uncertainty in the representations of the circum-arctic distribution of wetlands on the CH4 emission, several existing products were used to aggregate the emissions. Using the description of potential peatlands from the FAO Digital Soil Map of the World and the representation of floodplains by PCR-GLOBWB, the average annual flux over the period 2001-2006 was estimated to be 78 Tg yr(-1). In comparison, the six-year average CH4 fluxes were 37.7, 89.4, 145.6, and 157.3 Tg yr(-1) for different estimates of wetland extends based on the studies by Matthews and Fung, Prigent et al., Lehner and Doll, and Kaplan, respectively. This study shows the feasibility to estimate interannual variations in CH4 emissions by coupling hydrological and CH4 emission process models. It highlights the importance of an adequate understanding of hydrology in quantifying the total emissions from northern hemispheric wetlands and shows how knowledge of the sub-grid variability in wetland extent helps to prescribe relevant hydrological conditions to the emission model as well as to identify the uncertainty associated with existing wetland distributions. (Less)

112 citations


Journal ArticleDOI
01 Jul 2010
TL;DR: The authors showed that a significant portion of drylands occur over sedimentary basins hosting natural gas and oil reservoirs, where gas migration to the surface takes place, producing positive fluxes of methane into the atmosphere.
Abstract: Drylands are considered a net sink for atmospheric methane and a main item of the global inventories of the greenhouse gas budget. It is outlined here, however, that a significant portion of drylands occur over sedimentary basins hosting natural gas and oil reservoirs, where gas migration to the surface takes place, producing positive fluxes of methane into the atmosphere. New field surveys, in different hydrocarbon-prone basins, confirm that microseepage, enhanced by faults and fractures in the rocks, overcomes the methanotrophic consumption occurring in dry soil throughout large areas, especially in the winter season. Fluxes of a few units to some tens of mg m − 2 day − 1 are frequent over oil–gas fields, whose global extent is estimated at 3.5–4.2 million km 2 ; higher fluxes (> 50 mg m − 2 day − 1 ) are primarily, but not exclusively, found in basins characterized by macro-seeps. Microseepage may however potentially exist over a wider area (∼ 8 million km 2 , i.e. 15% of global drylands), including the Total Petroleum Systems, coal measures and portions of sedimentary basins that have experienced thermogenesis. Based on a relatively large and geographically dispersed data-set (563 measurements) from different hydrocarbon-prone basins in USA and Europe, upscaling suggests that global microseepage emission exceeding 10 Tg year − 1 is very likely. Microseepage is then only one component of a wider class of geological sources, including mud volcanoes, seeps, geothermal and marine seepage, which cannot be ignored in the atmospheric methane budget.

111 citations


Journal ArticleDOI
TL;DR: Gas hydrates are ice-like crystalline solids that form from mixtures of water and light natural gases such as methane, carbon dioxide, ethane, propane and butane as discussed by the authors.

108 citations


Journal ArticleDOI
TL;DR: It is suggested that global foliar CH(4) emissions from UV-irradiated pectin could account for 0.2-1.0 Tg yr(-1), of which 60% is from tropical latitudes, corresponding to <0.2% of total CH( 4) sources.
Abstract: Summary •Several studies have reported in situ methane (CH4) emissions from vegetation foliage, but there remains considerable debate about its significance as a global source. Here, we report a study that evaluates the role of ultraviolet (UV) radiation-driven CH4 emissions from foliar pectin as a global CH4 source. •We combine a relationship for spectrally weighted CH4 production from pectin with a global UV irradiation climatology model, satellite-derived leaf area index (LAI) and air temperature data to estimate the potential global CH4 emissions from vegetation foliage. •Our results suggest that global foliar CH4 emissions from UV-irradiated pectin could account for 0.2–1.0 Tg yr−1, of which 60% is from tropical latitudes, corresponding to < 0.2% of total CH4 sources. •Our estimate is one to two orders of magnitude lower than previous estimates of global foliar CH4 emissions. Recent studies have reported that pectin is not the only molecular source of UV-driven CH4 emissions and that other environmental stresses may also generate CH4. Consequently, further evaluation of such mechanisms of CH4 generation is needed to confirm the contribution of foliage to the global CH4 budget.

Journal ArticleDOI
TL;DR: In this article, space-borne observations indicate that tank bromeliads, herbaceous plants common throughout tropical forests, emit methane and may contribute to the tropical source of CO 2.
Abstract: Methane concentrations above tropical forests in the neotropics are high, according to space-borne observations. Flux measurements in the field suggest that tank bromeliads, herbaceous plants common throughout tropical forests, emit methane and may contribute to the tropical source.

Journal ArticleDOI
12 Nov 2010-Science
TL;DR: An atmospheric chemistry model was used to show how nitrous oxide emissions lower the concentration of tropospheric methane through a chain of chemical reactions that include stratospheric ozone depletion, changes in solar ultraviolet radiation fluxes, altered fluxes of ozone transport from the stratosphere to the troposphere, and increases in the amount of Tropospheric hydroxyl radicals.
Abstract: Nitrous oxide (N(2)O) and methane (CH(4)) are chemically reactive greenhouse gases with well-documented atmospheric concentration increases that are attributable to anthropogenic activities. We quantified the link between N(2)O and CH(4) emissions through the coupled chemistries of the stratosphere and troposphere. Specifically, we simulated the coupled perturbations of increased N(2)O abundance, leading to stratospheric ozone (O(3)) depletion, altered solar ultraviolet radiation, altered stratosphere-to-troposphere O(3) flux, increased tropospheric hydroxyl radical concentration, and finally lower concentrations of CH(4). The ratio of CH(4) per N(2)O change, -36% by mole fraction, offsets a fraction of the greenhouse effect attributable to N(2)O emissions. These CH(4) decreases are tied to the 108-year chemical mode of N(2)O, which is nine times longer than the residence time of direct CH(4) emissions.

Journal ArticleDOI
TL;DR: In this article, the authors report results from a greenhouse mesocosm study that indicate significant emissions of anaerobically produced CH4 transmitted to the atmosphere through broadleaf riparian tree species grown under flooded conditions.
Abstract: [1] Recent studies indicate that plants may be a previously overlooked but significant source of atmospheric CH4, though there is considerable disagreement on the mechanism of production. Our work sought to verify that woody deciduous trees grown under inundated conditions had the capacity for transporting CH4 from an anaerobic subsurface to the atmosphere and to consider if such a source could be important globally. Here, we report results from a greenhouse mesocosm study that indicate significant emissions of anaerobically produced CH4 transmitted to the atmosphere through broadleaf riparian tree species grown under flooded conditions. Using a leaf area normalized mean emission rate (0.7 ± 0.3 μg cm−2 hr−1), results were scaled globally for flooded forest regions and estimated to be 60 ± 20 Tg year−1, ∼10% of the global CH4 source. The carbon isotopic composition of CH4 emitted was found to be significantly enriched compared with expectations (δ13C ∼ −54‰) and provided an important isotopic constraint on the global source which coincides with the mean of the globally scaled greenhouse-based estimate.

Journal ArticleDOI
TL;DR: In this article, the authors used the relationship between changes in southern European tree populations and atmospheric methane concentrations in previous interglacials to evaluate the natural vs. anthropogenic contribution to Holocene methane emissions and assess the two alignment schemes.
Abstract: . Marine Isotope Stage (MIS) 11 has been considered a potential analogue for the Holocene and its future evolution. However, a dichotomy has emerged over the precise chronological alignment of the two intervals, with one solution favouring a synchronization of the precession signal and another of the obliquity signal. The two schemes lead to different implications over the natural length of the current interglacial and the underlying causes of the evolution of greenhouse gas concentrations. Here, the close coupling observed between changes in southern European tree populations and atmospheric methane concentrations in previous interglacials is used to evaluate the natural vs. anthropogenic contribution to Holocene methane emissions and assess the two alignment schemes. Comparison of the vegetation trends in MIS 1 and MIS 11 favours a precessional alignment, which would suggest that the Holocene is nearing the end of its natural course. This, combined with the divergence between methane concentrations and temperate tree populations after 5 kyr BP, provides some support for the notion that the Holocene methane trend may be anomalous compared to previous interglacials. In contrast, comparison of MIS 1 with MIS 19, which may represent a closer astronomical analogue than MIS 11, leads to substantially different conclusions on the projected natural duration of the current interglacial and the extent of the anthropogenic contribution to the Holocene methane budget. As answers vary with the choice of analogue, resolution of these issues using past interglacials remains elusive.

Journal ArticleDOI
TL;DR: In this article, the backscatter strength of a multibeam system was integrated with single-beam data to estimate the amount of seeps/m2 for different back-scatter intensities, resulting in 2709 vents in total.
Abstract: Bubble transport of methane from shallow seep sites in the Black Sea west of the Crimea Peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling. Ship-based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor. Here, the backscatter strength of a multibeam system was integrated with single-beam data to estimate the amount of seeps/m2 for different backscatter intensities, resulting in 2709 vents in total. Direct flux measurements by submersible revealed methane fluxes from individual vents of 0.32–0.85 l/min or 14.5–37.8 mmol/min at ambient pressure and temperature conditions. A conservative estimate of 30 mmol/min per site was used to estimate the flux into the water to be 1219–1355 mmol/s. The flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth, temperature, gas composition, and bubble size spectra into account. The flux into the atmosphere (3930–4533 mol/d) or into the mixed layer (6186–6899 mol/d) from the 21.8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods (1030–2495 mol/d). The amount of methane dissolving in the mixed layer is 2256–2366 mol/d. This close match shows that the hydroacoustic approach for extrapolating the number of seeps/m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas.

Journal ArticleDOI
25 Jun 2010-Science
TL;DR: Evidence is presented from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger events 7 and 8, and box modeling supports boreal wetland emissions as the most likely explanation for the interstadial increase.
Abstract: The causes of past changes in the global methane cycle and especially the role of marine methane hydrate (clathrate) destabilization events are a matter of debate. Here we present evidence from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane [δD(CH4)] that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger (DO) events 7 and 8. Box modeling supports boreal wetland emissions as the most likely explanation for the interstadial increase. Moreover, our data show that δD(CH4) dropped 500 years before the onset of DO 8, with CH4 concentration rising only slightly. This can be explained by an early climate response of boreal wetlands, which carry the strongly depleted isotopic signature of high-latitude precipitation at that time.

Journal ArticleDOI
TL;DR: In this article, the authors measured dissolved methane and nitrous oxide in seawater along a 6700 km transect of the North-West Passage between the North Atlantic Ocean and Beaufort Sea in the Arctic Ocean.

Journal ArticleDOI
TL;DR: Conversion of forests to farmland permanently lowers atmospheric methane consumption due to unresolved reasons, suggesting a shift from oligotrophic to copiotrophic species.
Abstract: Conversion of forests to farmland permanently lowers atmospheric methane consumption due to unresolved reasons. Alphaproteobacterial methanotrophs were predominant in forested soils and gammaproteobacterial species were predominant in farmland soils of subtropical ferralsols in Brazil. The capability of atmospheric methane consumption was obliterated in farmland soils, suggesting a shift from oligotrophic to copiotrophic species.

BookDOI
12 Aug 2010
TL;DR: In this paper, the authors provide a comprehensive and balanced overview of current knowledge of sources of methane and how these might be controlled to limit future climate change and highlight the potential to contribute significantly to climate change mitigation in the 21st century.
Abstract: Methane is a powerful greenhouse gas and is estimated to be responsible for approximately one-fifth of man-made global warming. Per kilogram, it is 25 times more powerful than carbon dioxide over a 100-year time horizon -- and global warming is likely to enhance methane release from a number of sources. Current natural and man-made sources include many where methane-producing micro-organisms can thrive in anaerobic conditions, particularly ruminant livestock, rice cultivation, landfill, wastewater, wetlands and marine sediments. This timely and authoritative book provides the only comprehensive and balanced overview of our current knowledge of sources of methane and how these might be controlled to limit future climate change. It describes how methane is derived from the anaerobic metabolism of micro-organisms, whether in wetlands or rice fields, manure, landfill or wastewater, or the digestive systems of cattle and other ruminant animals. It highlights how sources of methane might themselves be affected by climate change. It is shown how numerous point sources of methane have the potential to be more easily addressed than sources of carbon dioxide and therefore contribute significantly to climate change mitigation in the 21st century.

Journal ArticleDOI
TL;DR: The deep biocover demonstrated substantial reductions for nonmethane hydrocarbon emissions with high percentages of negative fluxes for several hydrocarbon groups, especially the aromatics, alkanes, and lower chlorinated compounds.
Abstract: Methane-oxidizing “biocovers” were constructed at the Leon County Landfill (Florida). The primary goal was to determine if a biocover placed above the existing thin (15 cm) intermediate clay cover would be capable of mitigating CH4 and nonmethane hydrocarbon (NMHC) emissions to the atmosphere in this subtropical environment. A secondary goal was to maximize the use of locally recycled materials for biocover construction. The biocovers consisted of 30 or 60 cm of ground garden waste placed over a 15 cm gas distribution layer (clean crushed recycled glass from discarded fluorescent lights). The deep biocover reduced methane fluxes relative to the controls during temporal monitoring over more than a year; in large part, these reductions were attributable to increased methane oxidation. Both the shallow and the deep biocover exhibited significant percentages of negative fluxes (uptake of atmospheric methane) relative to the nonbiocover controls which had consistently positive fluxes. The overall annual effect...

Journal ArticleDOI
05 Mar 2010-Science
TL;DR: Two observational studies shed light on how natural sources of methane emissions from sources such as wetlands may change in today's changing climate.
Abstract: Methane is, after water vapor and carbon dioxide, the third most important greenhouse gas in the atmosphere. Its concentration in the atmosphere has more than doubled since preindustrial times. Human energy production and use, landfills and waste, cattle raising, rice agriculture, and biomass burning are considered responsible for this increase ( 1 ). However, ∼40% of current global methane sources are natural. Most natural emissions come from anaerobic decomposition of organic carbon in wetlands, with poorly known smaller contributions from the ocean, termites, wild animals, wildfires, and geological sources. Two observational studies now shed light on how these natural sources are changing in today's changing climate ( 2 , 3 ).

Journal ArticleDOI
TL;DR: In this paper, the authors estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled atmosphere-ocean and atmosphere-vegetation models.
Abstract: [1] It is an open question to what extent wetlands contributed to the interglacial-glacial decrease in atmospheric methane concentration. Here we estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled atmosphere-ocean and atmosphere-ocean-vegetation models. These simulations apply improved boundary conditions resulting in better agreement with paleoclimatic data than earlier PMIP1 simulations. Emissions are computed from the dominant controls of water table depth, soil temperature, and plant productivity, and we analyze the relative role of each factor in the glacial decline. It is found that latitudinal changes in soil moisture, in combination with ice sheet expansion, cause boreal wetlands to shift southward in all simulations. This southward migration is instrumental in maintaining the boreal wetland source at a significant level. The mean emission temperature over boreal wetlands drops by only a few degrees, despite the strong overall cooling. The temperature effect on the glacial decline in the methane flux is therefore moderate, while reduced plant productivity contributes equally to the total reduction. Model results indicate a relatively small boreal and large tropical source during the LGM, with wetlands on the exposed continental shelves mainly contributing to the tropical source. This distribution in emissions is consistent with the low interpolar difference in glacial methane concentrations derived from ice core data.

Journal ArticleDOI
01 May 2010-Icarus
TL;DR: In this paper, the authors report results of laboratory studies of methane adsorption onto JSC-Mars-1, a martian soil simulant, and suggest that this process could explain the observations.

Journal ArticleDOI
David van der Ha1, Sven Hoefman1, Pascal Boeckx1, Willy Verstraete1, Nico Boon1 
TL;DR: The results obtained demonstrate that the treatment of methane-saturated effluents, even those with increased ammonium and salt levels, can be mitigated by implementation of Methane-oxidizing microbial consortia.
Abstract: Effluents of anaerobic digesters are an underestimated source of greenhouse gases, as they are often saturated with methane. A post-treatment with methane-oxidizing bacterial consortia could mitigate diffuse emissions at such sites. Semi-continuously fed stirred reactors were used as model systems to characterize the influence of the key parameters on the activity of these mixed methanotrophic communities. The addition of 140 mg L(-1) NH (4) (+) -N had no significant influence on the activity nor did a temperature increase from 28 degrees C to 35 degrees C. On the other hand, addition of 0.64 mg L(-1) of copper(II) increased the methane removal rate by a factor of 1.5 to 1.7 since the activity of particulate methane monooxygenase was enhanced. The influence of different concentrations of NaCl was also tested, as effluents of anaerobic digesters often contain salt levels up to 10 g NaCl L(-1). At a concentration of 11 g NaCl L(-1), almost no methane-oxidizing activity was observed in the reactors without copper addition. Yet, reactors with copper addition exhibited a sustained activity in the presence of NaCl. A colorimetric test based on naphthalene oxidation showed that soluble methane monooxygenase was inhibited by copper, suggesting that the particulate methane monooxygenase was the active enzyme and thus more salt resistant. The results obtained demonstrate that the treatment of methane-saturated effluents, even those with increased ammonium (up to 140 mg L(-1) NH (4) (+) -N) and salt levels, can be mitigated by implementation of methane-oxidizing microbial consortia.

Journal ArticleDOI
TL;DR: In this paper, the authors determined methane emissions in a field enclosure experiment in a littoral freshwater marsh composed of Phragmites australis were measured with funnel traps deployed in a series of enclosures for two 3 week periods.
Abstract: We determined methane (CH4) emissions in a field enclosure experiment in a littoral freshwater marsh under the influence of experimentally simulated warming and enhanced nitrogen deposition. Methane emissions by ebullition from the marsh composed of Phragmites australis were measured with funnel traps deployed in a series of enclosures for two 3 week periods. Diffusive fluxes were estimated on the basis of measured CH4 concentrations and application of Fick's law. Neither diffusive nor ebullitive fluxes of methane were significantly affected by warming or nitrate enrichment, possibly because variability both within and among replicate experimental enclosures was high. Average emission rates resulted primarily from ebullition (0.2–30.3 mmol CH4 m−2 d−1), which were 4 orders of magnitude higher than estimated diffusive fluxes and were of similar importance as the coarsely estimated advective methane transport through plants. Significant correlations between dissolved oxygen and dissolved methane and ebullition flux suggest that methane release from the sediment might feed back positively on methane production by reducing dissolved oxygen in the water column and oxygen flux into the sediment. Nitrate may have a similar effect. Extrapolation of our limited data indicates that total methane fluxes from vegetated littoral zones of temperate lakes may contribute 0.5%–7% of the global natural CH4 emissions. These results emphasize the importance of freshwater marshes as sources of methane emissions to the atmosphere, even when they occupy only relatively small littoral areas. More detailed investigations are clearly needed to assess whether global warming and nitrogen deposition can have climate feedbacks by altering methane fluxes from these wetlands.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the water column of the north-western Black Sea during the summers of 2003 and 2004, collecting water samples along a transect which crosses three methane seep areas in 90, 220, and 600 m water depth.

Journal ArticleDOI
TL;DR: The carbon isotopic composition of pore water carbon dioxide from Sallie's Fen, a New Hampshire poor fen, is measured to suggest that much of the methane produced during this time comes either from the unsaturated peat, or from the top 1-3 cm of saturated peat where episodic exchange with the atmosphere makes it invisible to the method.
Abstract: We measured the carbon isotopic composition of pore water carbon dioxide from Sallie's Fen, a New Hampshire poor fen. The isotope profiles are used in combination with a one-dimensional diffusion-reaction model to calculate rates of methane production, oxidation and transport over an annual cycle. We show how the rates vary with depth over a seasonal cycle, with methane produced deeper during the winter months and at progressively shallower depths into the summer season. The rates of methane production, constrained by the measured delta(13)C(dic) profiles, cannot explain high methane emission during the summer. We suggest that much of the methane produced during this time comes either from the unsaturated peat, or from the top 1-3 cm of saturated peat where episodic exchange with the atmosphere makes it invisible to our method.

Journal ArticleDOI
TL;DR: The diurnal variation in methane emission from alpine wetland vegetation could be attributable to changes in CH4 oxidation and production driven by plant gas transport mechanism, and has important implications for sampling and scaling strategies for estimating methane emission.
Abstract: Alpine wetland is a source for CH(4), but little is known about methane emission from such wetland, especially about its diurnal pattern. In this study we tried to probe the diurnal variation in methane emission from alpine wetland vegetation. The average methane emission rate was 9.6 +/- 3.4 mg CH(4) m (-aEuro parts per thousand 2) h (-aEuro parts per thousand 1). There was an apparent diurnal variation pattern in methane emission with one minor peak at 06:00 and a major one at 15:00. The sunrise peak was consistent with a two-way transport mechanism for plants (convective at daytime and diffusive at night-time). CH(4) emission was found significantly correlated with redox potentials. The afternoon peak could not be explained by diurnal variation in soil temperature, but could be attributable to changes in CH(4) oxidation and production driven by plant gas transport mechanism. The results have important implications for sampling and scaling strategies for estimating methane emission from alpine wetlands.