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Freshwater lakes are increasingly recognized as significant sources of atmospheric methane (CH4), potentially offsetting the terrestrial carbon sink. We present the first study of dissolved CH4 distributions and lake-air flux from Lake Winnipeg, based on two-years of observations collected during all seasons. Methane concentrations across two years had a median of value of 24.6 nmol L-1 (mean: 41.6 ± 68.2 nmol L-1) and ranged between 5.0 and 733.8 nmol L-1, with a 2018 annual median of 24.4 nmol L-1 (mean: 46.8 ± 99.3 nmol L-1) and 25.1 nmol L-1 (mean: 38.8 ± 45.2 nmol L-1) in 2019. The median lake-air flux was 1.1 µmol m−2 h−1 (range: 0.46–70.1 µmol m−2h−1, mean: 2.9 ± 10.2 µmol m−2 h−1) in 2018, and 5.5 µmol m−2h−1 (range: 0.0–78.4 µmol m−2 h−1, mean: 2.7 ± 8.5 µmol m−2 h−1) in 2019, for a total diffusive emission of 0.001 Tg of CH4-C yr−1. We found evidence of consistent spatial variability, with higher concentrations near river inflows. Significant seasonal trends in CH4 concentrations were not observed, though fluxes were highest during the fall season due to strong winds. Our findings suggest Lake Winnipeg is a CH4 source of similar mean magnitude to Lake Erie, with lower concentrations and fluxes per unit area than smaller mid- to high-latitude lakes. Additional work is needed to understand the factors underlying observed spatial variability in dissolved gas concentration, including estimations of production and consumption rates in the water column and sediments.

Forest soils are the largest atmospheric methane (CH4) sinks in terrestrial ecosystems, but models simulating this uptake have considerable uncertainties. Soil organic matter derived from aboveground vegetation net primary productivity (NPP) significantly influences CH4 uptake; therefore, we propose that the incorporation of NPP into global CH4 uptake models will greatly improve model predictions.

Ice core records of atmospheric methane ( CH 4 ) and its isotopic composition provide important information about biogeochemical cycles in the past. Interpreting these data requires that they faithfully record the composition of the atmosphere. In this study, we describe anomalies of up to 30–40 ppb CH 4 that are only observed in dust-rich ( > ∼ 60 ng Ca/g ice), glacial-period ice measured with standard melt-refreeze methods. The stable isotopic composition of CH 4 is also significantly affected. Results from the GISP2 and NEEM ice cores from Greenland show that excess CH 4 is either released or produced in the presence of liquid water in amounts which are highly correlated with the abundance of Ca 2 + and mineral dust in the sample. Additional experiments show that excess CH 4 is unaffected by the addition of HgCl 2 (a microbial inhibitor) and is not related to ice core storage time. Dust concentrations in Antarctic ice cores are an order of magnitude lower than in Greenlandic ice cores and no excess CH 4 was observed in samples from the Antarctic WAIS Divide (WD) and South Pole (SPICE) ice cores. While the overall structure of the ice core atmospheric methane history is minimally impacted by excess CH 4 , the impacts on the isotopic record and on inverse models used to reconstruct CH 4 sources are greater. We propose three potential mechanisms to explain the presence of excess CH 4 : (1) that CH 4 is adsorbed on dust particles prior to deposition on the ice sheet and is slowly desorbed during the melt-extraction step of sample analysis; (2) that dust acts as a micro-environment within the ice sheet for methanogenic extremophiles; or (3) that excess CH 4 is a product of abiotic degradation of organic compounds during the melt-extraction step of sample analysis.

Biological methane production occurs in anoxic terrestrial wetlands and in sulfate depleted marine sediments. It has been suggested that methanogens may have flourished in the anoxic and sulfate-poor environments of the Precambrian ocean, generating large amounts of methane that would have accumulated in the atmosphere and warmed the early Earth. However, modern ferruginous and sulfate-poor environments such as Lake Matano are not very efficient at generating methane, converting only about 5% of organic carbon to CH4 despite the lack of alternative remineralization pathways. We apply this restriction to a simple model of marine carbon cycling in order to generate new estimates of methane concentrations in the Precambrian atmosphere. Our results suggest that, if the ancient biosphere were similarly inefficient, atmospheric methane concentrations did not exceed 1 ppm, or about twice the pre-industrial value, at any time during the Proterozoic. Following the evolution of oxygenic photosynthesis, the maximum methane concentration in the Archean atmosphere was order 100 ppm, but no more than 1 ppm if steady state oxygen concentrations were greater than 10−8 present atmospheric levels. Substantially larger methane concentrations are only possible before the evolution of oxygenic photosynthesis.

Rice paddies are a significant source of atmospheric methane (CH4) threatening global warming. Methane fluxes from rice soils are mediated by both methanogens and methanotrophs, while subject to fertilization regimes. A field experiment was conducted to investigate the response of CH4 emissions, with a close link to methanogenic and methanotrophic communities, to different fertilization strategies over two consecutive rice growing seasons in a paddy field. Four fertilized treatments were established consisting of chemical phosphorous (P) and potassium (K) fertilizer (PK), chemical nitrogen (N) PK fertilizer (NPK), chemical NPK combined with organic manure (NPKM), and organic manure alone (M). Results showed that, relative to chemical PK treatment without N fertilizer input, the application of chemical NPK fertilizer, manure, and their combination significantly increased seasonal mean CH4 emissions by 67.4, 20.4 and 101.2%, respectively. Methane fluxes were significantly and positively (r2 = 0.75) related to mcrA gene copy numbers and the ratio of mcrA/pmoA, while negatively (r2 = 0.40) related to pmoA gene copy numbers, which was mainly regulated by the dynamics of water irrigation regime. The abundance of mcrA and pmoA had trade-off relationship over the rice growing season. In comparison with PK fertilization, N fertilized treatments did not alter the seasonal trend of CH4 fluxes, but enhanced the source strength of CH4 emissions through increased mcrA abundances rather than reduced pmoA-dominated methanotrophic CH4 oxidation in rice paddies. In contrast, N fertilization showed no effect on pmoA abundance and associated methanotrophic community in rice paddies. Results highlight that, given the fertilizer-driven balance between methanogenic and methanotrophic communities, fertilization options with either chemical or organic N input stimulated CH4 emissions mainly through improving soil C substrate and methanogenic activities, especially under the combination of chemical and organic N fertilization in rice paddies.

Karst caves are considered a natural sink of atmospheric methane (CH 4 ). Studies generally focus on measuring CH 4 within the cave environment, and little information is available about the factors influencing CH 4 abundance, such as the surrounding vadose and saturated zones of the aquifer, inputs of carbon dioxide (CO 2 ) – a potential precursor of CH 4 – and methanotrophic bacteria, which is likely the main cause of CH 4 consumption. In this paper we report the first study of CH 4 budget in Nerja, one of the main karst caves in Spain, based on seasonal monitoring of CH 4 and CO 2 concentration and stable C isotopic ratio in the cave system, integrated with analogue data from the underlying and overlying saturated/vadose zone, and methanotrophic bacteria activity (rDNA and Polymerase Chain Reaction analyses) in cave sediments and water. The results show that the cave environment consumes, via methanotrophic activity and through γ- and α–Proteobacteria, CH 4 coming from both the atmosphere and the vadose/saturated zones of the aquifer, where it is produced microbially. However, vadose zone methanogenesis may seasonally exceed the methanotrophy capacity of the cave, resulting in a net CH 4 increase in it. This competition process may be an important factor limiting the sink potential of karst caves.

Aerobic methanotrophs in upland soils consume atmospheric methane, serving as a critical counterbalance to global warming; however, the biogeographic distribution patterns of their abundance and community composition are poorly understood, especial at a large scale. In this study, soils were sampled from 30 grasslands across >2000 km on the Qinghai-Tibetan Plateau to determine the distribution patterns of methanotrophs and their driving factors at a regional scale. Methanotroph abundance and community composition were analyzed using quantitative PCR and Illumina Miseq sequencing of pmoA genes, respectively. The pmoA gene copies ranged from 8.2 × 10 5 to 1.1 × 10 8 per gram dry soil. Among the 30 grassland soil samples, Upland Soil Cluster Gamma (USCγ) dominated the methanotroph communities in 26 samples. Jasper Ridge Cluster (JR3) was the most dominant methanotrophic cluster in two samples; while Methylocystis, cluster FWs, and Methylobacter were abundant in other two wet soil samples. Interestingly, reanalyzing the pmoA genes sequencing data from existing publications suggested that USCγ was also the main methanotrophic cluster in grassland soils in other regions, especially when their mean annual precipitation was

Between 2012 and 2015, a severe drought and the consequent decrease in water supply in the southeastern region of Brazil reached concerning levels, leading to a water crisis. This situation caused aerial exposure of some reservoirs drawdown zone. This study aims to measure methane fluxes emitted by this drawdown zone along the Funil hydropower reservoir, Rio de Janeiro, Brazil. It was observed that there was a temporal variation of the methane flux in the sediments exposed in the three scenarios studied: drought, flooding and full (0.43, −0.31 and −0.01 mg CH4 m-2 h-1, respectively). The CH4 flux by area in the scenario with the highest exposed sediment area was 0.195 ton CH4 d-1. Considering the values recorded, the contribution of these emissions must become considered in the overall balance of methane in the atmosphere as a new pathway by reservoirs, mainly with the expected forecasts and possible cycles of droughts that may occur frequently. However, the temporal variability of these fluxes indicated the need for future monitoring initiatives that seek to understand how climate change affects the biochemical processes within the exposed sediments of drawdown zones.

Rice paddy fields are importan t sources of atmospheric methane (CH 4 ), and nitrous oxide (N 2 O) . In our previous study, we found that greenhouse gas emissions varied among rice varieties. Dissolved organic matter (DOM) is one of the most reactive organic matter fractions in an ecosystem. However, the relation between greenhouse gas emissions and DOM propertie s among rice varieties in paddy fields remains unclear. Here, a two-year field experiment was conducted to investigate the dynamic changes in DOM characteristics in seven rice varieties and their relation to the CH 4 and N 2 O emissions. Among the seven rice varieties studied, those with lower DOC, NH 4 -N and NO 3 -N concentrations and higher dissolved phenol (DP) concentrations in DOM had lower CH 4 and N 2 O emissions. Structural equation modeling revealed that DOC and DP can indirectly regulate CH 4 emissions by influencing mcrA and pmoA gene abundance, and DOC also can indirect regulate N 2 O emissions by influencing AOB , nirS and nosZ gene abundance. Fourier transform infrared (FTIR) and t hree-dimensional fluorescence (EEM) spectroscopy analysis further indicated that DOM includes more O-H and C=O phenol and protein content. Tryptophan-like and tyrosine-like protein material could regulate CH 4 and N 2 O emissions, respectively, by influencing the abundance of microbial functional genes ( mcrA , pmoA , AOB , nirS and nosZ ). These results demonstrated that the differences in greenhouse gas emissions among different rice varieties were dependent on DOM properties and microbial abundance , providing a theoretical basis for mitigating greenhouse gas emissions in rice paddy fields.

The increase in frequency and severity of heat waves during the pre-monsoon season (March–May) over Northwest India in recent decades is alarming. This study investigates the causative mechanism for warming through the forcing induced by planetary albedo changes over Northwest India, a hotspot for land-cover change. We use satellite-measured planetary albedo (α) and satellite-derived land-use-land-cover (LULC) data to estimate the impact of LULC changes from 2001 to 2018 on α and the associated radiative forcing. Over Northwest India, significant area under native land-cover, viz., barren, shrub and grass-lands, has been converted to cropland. The associated land-cover-induced changes have perturbed the radiation-budget by modifying the absorption of shortwave radiation, thereby contributing to the pronounced reduction of α as observed over this region. The diurnal-mean α has decreased by 0.016 ± 0.001 from 2001 to 2018 during pre-monsoon season which dominates α-decrease during the annual cycle over this region and contributes to the overall decreasing trend over India. Conversion of barren and shrub-lands to cropland is observed to be the greatest contributor to the α-decrease as compared to other land-cover changes. The radiative forcing due to decline in diurnal-mean α over Northwest India from 2001 to 2018 is highest during pre-monsoon at 5.99 ± 0.34 W/m2. This α-induced forcing averaged over the global land surface (0.02 W/m2) is equivalent to the corresponding direct forcing from rise in atmospheric methane concentrations during this period. We find an enhancement in near-surface heating to be associated with change in α; the decreasing trend in α during pre-monsoon has substantially enhanced near-surface extreme effective temperatures by 3.15 ± 2.61 K thus far and may further lead to more extreme heatwaves in future. Further, our findings highlight a decreasing (warming) and increasing (cooling) trend in clear-sky planetary albedo respectively over Northwest India and coastal regions, suggesting that sudden climate change could occur if one forcing dominates over the other.

Geological hydrocarbon gas seepage is a major global source of atmospheric methane, ethane and propane as greenhouse gases and photochemical pollutants. Natural gas seepage is generally related to faults and associated fracture intensification domains that provide conduits for natural gas from reservoir rocks to migrate upward and enter the atmosphere. In this study, we compare the case of intense gas seepage stemming directly from source rocks, mostly organic-rich fractured black shales in western New York State (NYS) versus areas with rare seepage in the more southern regions of the Appalachian Basin and the Midwest USA. In addition to thermogenic methane, western NYS shale gas seeps emit ethane and propane with C_(2+3) gas concentrations reaching up to 35 vol%. Fractures in NYS developed, reactivated and maintained permeability for gas as a result of Quaternary glaciation and post-glacial basin uplift. In contrast, the Appalachian regions farther south and the southern Midwest regions experienced less glacial loading and unloading than in NYS, resulting in less recent natural fracturing, as witnessed by the rarity of seepage on surface outcrops and in caves overlying gas-bearing shales and coals. The historical literature suggests that early western NYS drilling and production of oil and gas diminished shale gas pressure and resulted in declining gas seepage rates. Our survey documented 12 active western NYS natural gas seeps, whereas >32 seeps have been reported or documented since the 17th century. Preliminary tests showed that SCIAMACHY satellite data did not detect atmospheric methane anomalies over western NYS seeps.

The apparent activation energy of silicate weathering is a key parameter for understanding the regulation of atmospheric CO2 and surface-temperature of the Earth. Combining the atmospheric composition effects on the apparent activation energy with the compensation law for silicate-weathering flux, the relationship between the temperature dependence of atmospheric CO2 ( Δ H C O 2 ′ ), temperature (T) and silicate-weathering flux ( F C O 2 ) has been recently established ( Kanzaki and Murakami, 2018 ). The present study examined the effects of atmospheric CO2 and CH4 on silicate weathering in the Precambrian based on the above T- Δ H C O 2 ′ - F C O 2 relationship and the greenhouse effects of CO2, which represent Δ H C O 2 ′ on the global scale, with and without the presence of CH4. Calculation of the ratio of the change in F C O 2 to the corresponding change in the partial pressure of atmospheric CO2 ( P C O 2 ) as an indicator of the silicate-weathering feedback on CO2 revealed hitherto unknown weathering-climate interplays. The states where P C O 2 ∼30 °C are unstable due to the positive feedback, and immediately change with slight CO2 changes to either the states of P C O 2 > 10−0.5 atm or those of P C O 2 The temperature and P C O 2 transitions in the Precambrian were finally calculated based on the relationship between Δ H C O 2 ′ , T and F C O 2 and the greenhouse effects of CO2. The calculated CO2 levels are high enough that the temperature could have been maintained at >0 °C only by CO2 through the Precambrian. The consistent P C O 2 estimates from paleosols (fossil weathering profiles) in the literature support the argument. The calculated temperatures suggest that the Earth could have been cool to hot until around the end of Archean and cool to moderate afterwards.

Aquaculture ponds are of increasing worldwide concerns as critical sources of atmospheric methane (CH4) and nitrous oxide (N2O), but little is known about these gases emissions as affected by aquaculture species, stocking and water management in aquaculture ponds. Here, a two-year study was carried out to quantify CH4 and N2O emissions from freshwater crab and fish aquaculture ponds in subtropical China. We further explored how the microbial functional genes [CH4: mcrA and pmoA; N2O: archaeal and bacterial amoA (AOA + AOB), nirS, nirK, nosZ] may drive CH4 and N2O release in the crab aquaculture pond typically undergoing flooding-to-drainage alteration. Over the two-year period, annual CH4 and N2O fluxes averaged 0.95 mg m−2 h−1 and 20.94 μg m−2 h−1 in the fish aquaculture, and 0.78 mg m−2 h−1and 28.48 μg m−2 h−1 in the crab aquaculture, respectively. The direct N2O emission factors were estimated to be 0.77% and 0.36% of the total N input by feed or 1.59 g N2O-N kg−1 and 1.06 g N2O-N kg−1 aquaculture yield in the crab and fish ponds, respectively. Among three functional stocking areas, CH4 and N2O emissions were consistently the highest at the feeding area (FA) in the both aquaculture ponds, followed by at the undisturbed area (UA) and aerated area (AA). The shift in sediment soil moisture from waterlogging to drainage conditions significantly increased the abundance of AOB relative to AOA and pmoA, decreased those of denitrifying functional genes (nirS, nirK, nosZ) and mcrA, while did not alter the functional group ratio of nirS + nirK relative to nosZ. Our results highlight that a better understanding of CH4 and N2O emissions from aquaculture ponds requires taking into consideration of data sourced from more diverse aquaculture systems with different management patterns. In addition, a deep analysis of the microbial processes that drive CH4 and N2O production and consumption from aquaculture ponds remains to be addressed in future studies.

The rapid increase of natural gas consumption has induced imbalance between supply and demand of natural gas, and the continuous growth of methane emissions has severely exacerbated greenhouse effects and destroyed the atmospheric methane cycle. High-efficiency CH4 capture and separation from N2 rich gases has become a significant challenge for the recovery and utilization of low-grade natural gas and also industrial tail gas, which was important for sustainable energy and environment and attracted much attention from both researchers and engineers in recent years. This review provides an overview of selective separation techniques for N2 removal from natural gas including the benefits and drawbacks of these typical methods. Most notably, the review primarily outlines the progress of metal-organic frameworks, zeolites and activated carbons as superior adsorbents for separating CH4-N2 mixtures in worldwide laboratories, respectively, with an emphasis on the relationship of the pore size, surface chemistry and composition of adsorbents with the CH4/N2 selectivity and methane capacity. We also highlight the potential for the development of the new adsorbents with the best possible matching between aperture control and atomic-scale tuning of the composition for CH4 capture and separation from N2 rich gases, and indicate that the MOFs possess both the advantages of activated carbons and zeolites and will become one of the most promising candidates for high-efficiency CH4 separation from N2 rich gases in the future.

Atmospheric methane has been increasing since the beginning of the industrial era due to anthropogenic emissions. Methane has many sources, both natural and anthropogenic, and there continues to be considerable uncertainty regarding the contribution of each source to the total methane budget. Thus, remote sensing techniques for monitoring and measuring methane emissions are of increasing interest. Recently, the Airborne Visible-Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) has proven to be a valuable instrument for quantitative mapping of methane plumes. Despite this success, uncertainties remain regarding the sensitivity of the retrieval algorithms, including the influence of albedo and the impact of surfaces that may cause spurious signals. To explore these sensitivities, we applied the Iterative Maximum a Posterior Differential Optical Absorption Spectroscopy (IMAP-DOAS) methane retrieval algorithm to synthetic reflected radiances with variable methane concentrations, albedo, surface cover, and aerosols. This allowed for characterizing retrieval performance, including potential sensitivity to variable surfaces, low albedo surfaces, and surfaces known to cause spurious signals. We found that dark surfaces (below 0.10 μWcm^(−2)nm^(−1)sr^(−1) at 2139 nm), such as water and green vegetation, and materials with absorption features in the 2200–2400 nm range caused higher errors in retrieval results. We also found that aerosols have little influence on retrievals in the SWIR. Results from the synthetic scene are consistent with those observed in IMAP-DOAS retrievals for real AVIRIS-NG scenes containing methane plumes from a waste dairy lagoon and coal mine ventilation shafts. Understanding the effect of surface properties on methane retrievals is important given the increased use of AVIRIS-NG to map gas plumes from a diversity of sources over variable landscapes.

Natural wetlands are the largest source of methane emissions, contributing 20–40% of global emissions and dominating the inter-annual variability. Large uncertainties remain on their variability and response to climate change. This study uses atmospheric methane observations from the GOSAT satellite to evaluate methane wetland emission estimates. We assess how well simulations reproduce the observed methane inter-annual variability by evaluating the detrended seasonal cycle. The latitudinal means agree well but maximum differences in the tropics of 28.1–34.8 ppb suggest that all simulations fail to capture the extent of the tropical wetland seasonal cycle. We focus further analysis on the major natural wetlands in South America: the seasonally flooded savannah of the Pantanal (Brazil) and Llanos de Moxos (Bolivia) regions; and the riverine wetlands formed by the Parana River (Argentina). We see large discrepancies between simulation and observation over the Pantanal and Llanos de Moxos region in 2010, 2011 and 2014 and over the Parana River region in 2010 and 2014. We find highly consistent behaviour between the time and location of these methane anomalies and the change in wetland extent, driven by precipitation related to El Nino Southern Oscillation activity. We conclude that the inability of land surface models to increase wetland extent through overbank inundation is the primary cause of these observed discrepancies and can lead to under-estimation of methane fluxes by as much as 50% (5.3–11.8 Tg yr−1) of the observed emissions for the combined Pantanal and Parana regions. As the hydrology of these regions is heavily linked to ENSO variability, being able to reproduce changes in wetland behaviour is important for successfully predicting their methane emissions.

Paddy soil accounts for 10% of global atmospheric methane (CH4) emissions. Many types of fertilizers may enhance CH4 emissions, especially organic fertilizer. The aim of this study was to explore the effects of different fertilizers on CH4 and methanogen patterns in paddy soil. This experiment involved four treatments: chemical fertilizer (CT), organic fertilizer (OT), mixed with chemical and organic fertilizer (MT), and no fertilizer (ctrl). The three fertilization treatments were applied with total nitrogen at the same rate of 300 kg N ha−1. Paddy CH4, soil physicochemical variables and methanogen communities were quantitatively analyzed. Rhizosphere soil mcrA and pmoA gene copy numbers were determined by qPCR. Methanogenic 16S rRNA genes were identified by MiSeq sequencing. The results indicated CH4 emissions were significantly higher in OT (145.31 kg ha−1) than MT (84.62 kg ha−1), CT (77.88 kg ha−1) or ctrl (32.19 kg ha−1). Soil organic acids were also increased by organic fertilization. CH4 effluxes were significantly and negatively related to mcrA and pmoA gene copy numbers, and positively related to mcrA/pmoA. Above all, hydrogenotrophic Methanocella and acetoclastic Methanosaeta were the predominant methanogenic communities; these communities were strictly associated with soil potassium, oxalate, acetate, and succinate. Application of organic fertilizer promoted the dominant acetoclastic methanogens, but suppressed the dominant hydrogenotrophic methanogens. The transformation in methanogenic community structure and enhanced availability of C substrates may explain the increased CH4 production in OT compared to other treatments. Compared to OT, MT may partially mitigate CH4 emissions while guaranteeing a high rice yield. On this basis, we recommend the local fertilization pattern should change from 300 N kg ha−1 of organic manure to the same level of mixed fertilization. Moreover, we suggest multiple combinations of mixed fertilization merit more investigation in the future.

The present study examines the spatiotemporal variability and interrelations of the atmospheric methane (CH4), carbon monoxide (CO) and biomass burning (BB) outbreaks retrieved from satellite data over the Amazon region during the 2003–2012 period. In the climatological context, we found consistent seasonal cycles of BB outbreaks and CO in the Amazon, both variables showing a peak during the dry season. The dominant CO variability mode features the largest positive loadings in the southern Amazon, and describes the interannual CO variations related to BB outbreaks along the deforestation arc during the dry season. In line with CO variability and BB outbreaks, the results show strong correspondence with the spatiotemporal variability of CH4 in the southern Amazon during years of intense drought. Indeed, the areas with the largest positive CH4 anomalies in southern Amazon overlap the areas with high BB outbreaks and positive CO anomalies. The analyses also showed that high (low) BB outbreaks in the southern Amazon occur during dry (wet) years. In consequence, the interannual climate variability modulates the BB outbreaks in the southern Amazon, which in turn have considerable impacts on CO and CH4 interannual variability in the region. Therefore, the BB outbreaks might play a major role in modulating the CH4 and CO variations, at least in the southern Amazon. This study also provides a comparison between the estimate of satellite and aircraft measurements for the CH4 over the southern Amazon, which indicates relatively small differences from the aircraft measurements in the lower troposphere, with errors ranging from 0.18% to 1.76%.

Shallow gas, here defined as free gas that is trapped in unconsolidated, deltaic and shallow marine siliciclastic sediments of Plio-Pleistocene age, is found within the topmost 1000 m of sediment in the southern North Sea. Shallow amplitude anomalies in seismic reflection data are likely due to the presence of gas. The most prominent and easy-to-recognize indicators are high-amplitude anomalies, or “bright spots”, that are widespread within the southern North Sea. Gas from shallow reservoirs is currently produced offshore The Netherlands. In this study, we determine whether there are analogous shallow gas accumulations within the German North Sea. Therefore, we screened 2D and 3D multichannel seismic data for shallow amplitude anomalies. Several clusters of bright spots are identified above salt domes that closely resemble the economic deposits known in the Dutch sector in both size and their characteristic multilayered shape. Three of these potential gas accumulations, occurring in combination with additional hydrocarbon indicators such as seismic attenuation and velocity push-downs, are investigated in detail and compared to shallow gas fields from offshore The Netherlands. Amplitude anomalies indicate gas seepage on the seafloor that may contribute to the atmospheric methane budget and may have an impact on offshore infrastructure.

The extensive use of natural gas (NG) in urban areas for heating and cooking and as a vehicular fuel is associated with potentially significant emissions of methane (CH4) to the atmosphere. Methane, a potent greenhouse gas that influences the chemistry of the atmosphere, can be emitted from different sources including leakage from NG infrastructure, transportation activities, end-use uncombusted NG, landfills and livestock. Although significant CH4 leakage associated with aging local NG distribution systems in the U.S. has been reported, further investigation is required to study the role of this infrastructure component and other NG-related sources in atmospheric CH4 enhancements in urban centers. In this study, neighborhood-scale mobile-based monitoring of potential CH4 emissions associated with NG in the Greater Houston area (GHA) is reported. A novel dual-gas 3.337 μm interband cascade laser-based sensor system was developed and mobile-mode deployed for simultaneous CH4 and ethane (C2H6) monitoring during a period of over 14 days, corresponding to ∼ 90 h of effective data collection during summer 2016. The sampling campaign covered ∼250 exclusive road miles and was primarily concentrated on eight residential zones with distinct infrastructure age and NG usage levels. A moderate number of elevated CH4 concentration events (37 episodes) with mixing ratios not exceeding 3.60 ppmv and associated with atmospheric background enhancements below 1.21 ppmv were observed during the field campaign. Source discrimination analyses based on the covariance between CH4 and C2H6 levels indicated the predominance of thermogenic sources (e.g., NG) in the elevated CH4 concentration episodes. The volumetric fraction of C2H6 in the sources associated with the thermogenic CH4 spikes varied between 2.7 and 5.9%, concurring with the C2H6 content in NG distributed in the GHA. Isolated CH4 peak events with significantly higher C2H6 enhancements (∼11%) were observed at industrial areas and locations with high density of petroleum and gas pipelines in the GHA, indicating potential variability in Houston's thermogenic CH4 sources.

The atmospheric methane growth rate has fluctuated over the past three decades, signifying variations in methane sources and sinks. Methane isotopic ratios ( δ 13 CH 4 ) differ between emission categories, and can therefore be used to distinguish which methane sources have changed. However, isotopic modelling studies have mainly focused on uncertainties in methane emissions rather than uncertainties in isotopic source signatures. We simulated atmospheric δ 13 CH 4 for the period 1990–2010 using the global chemistry-climate model SOCOL. Empirically-derived regional variability in the isotopic signatures was introduced in a suite of sensitivity simulations. These simulations were compared to a baseline simulation with commonly used global mean isotopic signatures. We investigated coal, natural gas/oil, wetland, livestock, and biomass burning source signatures to determine whether regional variations impact the observed isotopic trend and spatial distribution. Based on recently published source signature datasets, our calculated global mean isotopic signatures are in general lighter than the commonly used values. Trends in several isotopic signatures were also apparent during the period 1990–2010. Tropical livestock emissions grew during the 2000s, introducing isotopically heavier livestock emissions since tropical livestock consume more C4 vegetation than midlatitude livestock. Chinese coal emissions, which are isotopically heavy compared to other coals, increase during the 2000s leading to higher global values of δ 13 CH 4 for coal emissions. EDGAR v4.2 emissions disagree with the observed atmospheric isotopic trend for almost all simulations, confirming past doubts about this emissions inventory. The agreement between the modelled and observed δ 13 CH 4 interhemispheric differences improves when regional source signatures are used. Even though the simulated results are highly dependent on the choice of methane emission inventories, they emphasize that the commonly used global mean signatures are inadequate. Regional isotopic signatures should be employed in modelling studies that try to constrain methane emission inventories.

Inland aquaculture ponds have been documented as important sources of atmospheric methane (CH4) and nitrous oxide (N2O), while their regional or global source strength remains unclear due to lack of direct flux measurements by covering more typical habitat-specific aquaculture environments. In this study, we compared the CH4 and N2O fluxes from rice paddies and nearby inland fish aquaculture wetlands that were converted from rice paddies in southeast China. Both CH4 and N2O fluxes were positively related to water temperature and sediment dissolved organic carbon, but negatively related to water dissolved oxygen concentration. More robust response of N2O fluxes to water mineral N was observed than to sediment mineral N. Annual CH4 and N2O fluxes from inland fish aquaculture averaged 0.51 mg m−2 h−1 and 54.78 μg m−2 h−1, amounting to 42.31 kg CH4 ha−1 and 2.99 kg N2O-N ha−1, respectively. The conversion of rice paddies to conventional fish aquaculture significantly reduced CH4 and N2O emissions by 23% and 66%, respectively. The emission factor for N2O was estimated to be 0.46% of total N input in the feed or 1.23 g N2O-N kg−1 aquaculture production. The estimate of sustained-flux global warming potential of annual CH4 and N2O emissions and the net economic profit suggested that such conversion of rice paddies to inland fish aquaculture would help to reconcile the dilemma for simultaneously achieving both low climatic impacts and high economic benefits in China. More solid direct field measurements from inland aquaculture are in urgent need to direct the overall budget of national or global CH4 and N2O fluxes.

Biogas upgrading to natural gas quality has been under focus the recent years for increasing the utilization potential of biogas. Conventional methods for CO2 removal are expensive and have environmental challenges, such as increased emissions of methane in the atmosphere with serious greenhouse impact. In this study, an innovative microbial electrochemical separation cell (MESC) was developed to in-situ separate and regenerate CO2 via alkali and acid regeneration. The MESC was tested under different applied voltages, inlet biogas rates and electrolyte concentrations. Pure biomethane was obtained at 1.2 V, inlet biogas rate of 0.088 mL/h/mL reactor and NaCl concentration of 100 mM at a 5-day operation. Meanwhile, the organic matter of the domestic wastewater in the anode was almost completely removed at the end. The study demonstrated a new sustainable way to simultaneously upgrade biogas and treat wastewater which can be used as proof of concept for further investigation.

While temperate reservoirs can be a significant source of atmospheric methane (CH4), knowledge of the role they play in global emissions of the gas remains limited in line with extreme temporal and spatial variability noted both within and between reservoirs. There is also still no clear identification of the environmental factors influencing the emission of this gas to the atmosphere. This article presents the results of research into the influence of sedimenting matter on CH4 emission from the surface of different zones of reservoirs. The research were conducted in 2018-2019 within Maziarnia and Nielisz Reservoirs – two artificial bodies of water of eutrophic status both located in SE Poland. Their diffusive CH4 fluxes at the water-air interface were measured using the “static chamber” method, while sediment traps monitored the rate of accumulation of sedimenting matter in bottom sediments (US). The CH4 fluxes noted at the reservoirs proved highly variable, both temporally and spatially, ranging from 0.02 to over 2500 mmol/m2·d. Determined accumulation indexes were in turn in the 13.61-618.49 g/m2·d range. Nevertheless, CH4 flux was found to correlate significantly with sedimentation index (US), with highest observed values for both reservoirs noted in river zone, while the lowest characterise the lacustrine zone. On this basis, it was hypothesised that sedimentation index may prove a useful tool in estimating CH4 emissions from reservoirs, with the reverse relationship also likely to apply. Furthermore, the key factor found to be responsible for the aforementioned temporal and spatial variations in CH4 emissions is primary production, whose subsequent sedimentation supplies sediments with easily-degradable organic matter. The results presented here contribute to an understanding of environmental factors that may influence spatial variation in CH4 production and can be useful to serve determinate of potential methods by which to reduce emissions this gas from managed systems such as reservoirs.

Atmospheric methane emissions from anaerobic effluents represent a source of greenhouse gases that can be mitigated by biofiltration. This study performs a comprehensive analysis on methane biofiltration using compost as packing to determine the limiting phenomena. A mathematical model calibrated by heterogeneous respirometry predicted the temperature effects (15–40 °C) on the kinetics of mass transport and biological reaction in a methanotrophic biofilm. It was validated through experimentation from steady state continuous runs (elimination capacities from 38 to 50 g m−3 h−1 with removal efficiencies of 62–80%). Results from model validation showed no significant differences (p-value ≥ 0.05) between the experimental methane elimination capacities and those predicted by the model at inlet 21 g C H 4 m−3 (4% volume in air, at 20 °C and 0.78 atm). To assess the limiting phenomena, the global and biofilm effectiveness factors were evaluated. This analysis demonstrated a biofilm limitation, specifically due to methane diffusion within the biofilm at the conditions tested (19 min of empty bed residence time). Even if the optimal temperature for methane oxidation activity was between 25 and 30 °C, the lower reaction rates at other temperatures did not limit the methane biofiltration in the applied interval.

A high sensitivity sensor, combining a multipass cell and wavelength modulation spectroscopy in the near infrared spectral region was designed and implemented for trace gas detection. The effective length of the multipass cell was about 290 meters. The developed spectroscopic technique demonstrates an improved sensitivity of methane in ambient air and a relatively short detection time compared to previously reported sensors. Home-built electronics and software were employed for diode laser frequency modulation, signal lock-in detection and processing. A dual beam scheme and a balanced photo-detector were implemented to suppress the intensity modulation and noise for better detection sensitivity. The performance of the sensor was evaluated in a series of measurements ranging from three hours to two days. The average methane concentration measured in ambient air was 2.01 ppm with a relative error of ± 2.5%. With Allan deviation analysis, it was found that the methane detection limit of 1.2 ppb was achieved in 650 s. The developed sensor is compact and portable, and thus it is well suited for field measurements of methane and other trace gases.

Methanotrophic bacteria in soil serve as the only known biological sink of atmospheric methane, and impact net methane emission from soils. Most members of methanotrophs use particulate methane monooxygenase enzyme, encoded by the pmoA gene, to oxidize methane. Here, Illumina sequencing (iTAG) of pmoA gene was carried out to examine methanotrophic bacterial diversity in soils under different land use. Additionally, the effect of soil-type on pmoA amplicon sequence abundance was analyzed. Two sites in Ohio, each comprising of long-term no-tillage plots, plow-tillage plots, grassland, and forest were sampled. The tillage plots also included continuous-corn and corn-soybean crop rotations. By referencing a curated database of the pmoA gene, we were able to identify eight genera of methanotrophs with varying relative abundances in the samples. Additionally, four genera were differentially abundant across samples (alpha = 0.005) and included Methylocystis , Methylocococcus , Methylosoma , and USCa . About 30% of processed sequences were unclassified. Nonmetric multidimensional scaling (NMDS) of unweighted UniFrac and Bray-Curtis metrics showed clear community distinction based on sites. Soil type had the most significant effect (p

Methane emitted by insects is considered to be an important source of atmospheric methane. Here we report the stimulation of methane emission in the cockroach Periplaneta americana and termite Coptotermes chaohuensis, insects with abundant methanogens, by neonicotinoids, insecticides widely used to control insect pests. Cycloxaprid (CYC) and imidacloprid (IMI) caused foregut expansion in P. americana, and increased the methane emission. Antibiotics mostly eliminated the effects. In P. americana guts, hydrogen levels increased and pH values decreased, which could be significantly explained by the gut bacterium community change. The proportion of several bacterium genera increased in guts following CYC treatment, and two genera from four could generate hydrogen. Hydrogen is a central intermediate in methanogenesis. All increased methanogens in both foregut and hindgut used hydrogen as electron donor to produce methane. Besides, the up-regulation of mcrA, encoding the enzyme for the final step of methanogenesis suggested the enhanced methane production ability in present methanogens. In the termite, hydrogen levels in gut and methane emission also significantly increased after neonicotinoid treatment, which was similar to the results in P. americana. In summary, neonicotinoids changed bacterium community in P. americana gut to generate more hydrogen, which then stimulated gut methanogens to produce and emit more methane. The finding raised a new concern over neonicotinoid applications, and might be a potential environmental risk associated with atmospheric methane.

The Earth's polar regions are experiencing a greater frequency of freeze-thaw events throughout the polar summer, contributing to atmospheric methane and destabilising clay-rich sediments. Clays in soils tightly bind pore water and thus substantially modify freeze-thaw events. While temperatures of phase transitions for confined pore water may be precisely assessed using calorimetric or thermal analyses to −30 or −40 °C, neutron scattering directly probes how pores in clay minerals control ice formation and melting to lower temperatures. We apply elastic neutron scattering to accurately quantify the unfrozen water content of clay gels and unambiguously identify different pore-water environments by their freezing temperatures. Using this approach, we conclude that cryosuction controls water mobility in frozen soils in the absence of soluble salts to much lower temperatures than observed by other techniques. Dyanmics determined from neutron scattering indicates that water in clay gel pores thaws at much lower temperatures than currently considered, and thus pose potential risks for contaminant migration at sub freezing temperatures. The general poor strength of wet clays can significantly impact infrastructure in cold regions undergoing an increased frequency of freeze-thaw events.

Methane (CH4) is a prominent Greenhouse Gas (GHG) and its global atmospheric concentration has increased significantly since the year 2007. Anthropogenic CH4 emissions are projected to be 9390 million metric tonnes by 2020. Here, we present the long–term changes in atmospheric methane over India and suggest possible alternatives to reduce soil emissions from paddy fields. The increase in atmospheric CH4 concentrations from 2009 to 2020 in India is significant, about 0.0765 ppm/decade. The Indo-Gangetic Plains, Peninsular India and Central India show about 0.075, 0.076 and 0.074 ppm/decade, respectively, in 2009–2020. Seasonal variations in CH4 emissions depend mostly on agricultural activities and meteorology, and contribution during the agricultural intensive period of Kharif–Rabi (i.e., June–December) is substantial in this regard. The primary reason for agricultural soil emissions is the application of chemical fertilizers to improve crop yield. However, for rice farming, soil amendments involving stable forms of carbon can reduce GHG emissions and improve soil carbon status. High crop production in pot culture experiment resulted in lower potential yield–scaled GHG emissions in rice with biochar supplement. The human impact of global warming induced by agricultural activities could be reduced by using biochar as a natural solution.

Subterranean methanotrophy is a potentially important but overlooked sink for the atmospheric greenhouse gas methane (CH 4 ). This study documents a microbial CH 4 sink in tropical subterranean karst cavities in Vietnam's northern karst province where porosity, steep topography, and scarce soil and vegetation cover foster the exchange of subterranean air with the atmosphere. Our data are based on (i) surveys of CH 4 , carbon dioxide, and radon concentrations in the air of 11 caves, (ii) in situ mesocosm experiments in caves, as well as (iii) laboratory mesocosm measurements using sediment and rock from caves. The extent of CH 4 depletion in cave air depends on the ventilation rate and the availability of moisture to provide a habitat for CH 4 -oxidizing bacteria, both of which are seasonally variable in northern Vietnam and in part depend on monsoonal activity. Mesocosm experiments using fresh versus sterilized rock and sediment confirmed the role of microbial methanotrophy towards uptake of CH 4 from cave air. Our results also suggest that within-cave heterogeneity of environmental variables like salinity may affect rates of CH 4 oxidation. We conservatively estimate that 150,000 metric tons of atmospheric CH 4 are microbially oxidized annually in the ~ 29,000 km 2 of Vietnamese tropical karst, which would compensate for ~ 7% of Vietnam's agricultural CH 4 emissions from rice farming and livestock. Future studies estimating the global fluxes of the atmospheric greenhouse gas CH 4 should consider subterranean karst as a potentially important CH 4 sink.

Methane emissions from wetlands contribute to the currently rising levels of methane in the atmosphere. Nonetheless, the assessments of methane-producing Archaea (methanogens) and their environmental controls are still rare particularly in soils from estuarine tidal marshes. In estuarine tidal marshes, the salinity gradient is commonly observed, and its effects on the methanogenic community are hardly known. In this study, in the Min River estuary, southeast China, we analyzed two freshwater and two brackish (oligohaline) marshes in a subtropical estuary, where we assessed methanogenic community structure and abundance by molecular cloning, sequencing, and quantitative PCR methods, as well as by means of soil physicochemical characteristics and concentration of methane dissolved in pore water. The common and dominant genera of these methanogens include Methanoregula, Methanobacterium, Methanosarcina, and Methanolinea in the four marshes. Phylotypes of the methanogens using H2/CO2 (Methanomicrobiales) or acetate (Methanosarcinales) were identified in the mcrA gene clone libraries and by restriction fragment length polymorphism (RFLP) analyses. The abundance levels of methanogens in the two freshwater marshes were significantly higher than those in the two brackish marshes. The value of the Shannon Index (H′) of diversity and Simpson index (D) of evenness of methanogen mcrA clone libraries decreased along the salinity gradient from freshwater to brackish water. Methanogen community structure varied with soil depth in the four wetlands. The concentrations of methane in pore water also decreased from the freshwater sites to the brackish sites; this pattern is consistent with a change in the abundance of methanogens. Our results showed that in a low-level salinity gradient of a subtropical estuary, salinity is still a major factor controlling the overall community structure and abundance of methanogens.

Canada and Mexico have large but uncertain methane emissions from the oil/gas industry. Inverse analyses of atmospheric methane observations can improve emission estimates but require accurate source patterns as prior information. In order to serve this need, we develop a 0.1° × 0.1° gridded inventory of oil/gas emissions in Canada for 2013 and Mexico for 2010 by disaggregating national emission inventories using best available data for production, processing, transmission, and distribution. Results show large differences with the EDGAR v4.2 gridded global inventory used in past inverse analyses. Canadian emissions are concentrated in Alberta (gas production and processing) and Mexican emissions are concentrated along the east coast (oil production).

To what extent methane liberated from marine hydrate will enter the ocean during a warmer world is unknown. Although methane release due to hydrate dissociation has been modelled, it is unclear whether or not methane will reach the seafloor during a warmer world and therefore contribute to oceanic and atmospheric budgets. Here we show, using a new three-dimensional (3-D) seismic dataset, that some hydrate deposits surround the gas chimneys passing through the HSZ. Bottom water warming since the last glacial maximum (LGM) is interpreted to cause hydrate dissociation but critically some of the released methane was not vented to the ocean. The released gas caused seal failure and free gas entered the hydrate stability zone (HSZ) through vertical gas chimneys to where new hydrate accumulations formed. This process is a new evidence for methane recycling and could account in part for the lack of methane in ice core records that cover warming events during the late Quaternary. This research provides new insight into how methane could be recycled rather than vented during a warmer world.

We retrieve vertical and meridional variations of methane mole fraction in Titan's lower troposphere by re-analyzing near-infrared ground-based observations from 17 July 2014 UT (Adamkovics et al., 2016). We generate synthetic spectra using atmospheric methane profiles that do not contain supersaturation or discontinuities to fit the observations, and thereby retrieve minimum saturation altitudes and corresponding specific humidities in the boundary layer. We relate these in turn to surface-level relative humidities using independent surface temperature measurements. We also compare our results with general circulation model simulations to interpret and constrain the relationship between humidities and surface liquids. The results show that Titan's lower troposphere is undersaturated at latitudes south of 60N, consistent with a dry surface there, but increases in humidity toward the north pole indicate appreciable surface liquid coverage. While our observations are consistent with considerably more liquid methane existing at the north pole than is present in observed lakes, a degeneracy between low-level methane and haze leads to substantial uncertainty in determining the extent of the source region., Comment: Accepted for publication in Icarus

Life as we know it requires liquid water and sufficient liquid water is highly unlikely on the surface of present-day Mars. However, according to thermal models there is a possibility of liquid water in the deep subsurface of Mars. Thus, the martian subsurface, where the pressure and temperature is higher, could potentially provide a hospitable environment for a biosphere. Also, methane has been detected in the Mars’ atmosphere. Analogous to Earth’s atmospheric methane, martian methane could also be biological in origin. The carbon and energy sources for methanogenesis in the subsurface of Mars could be available by downwelling of atmospheric CO2 into the regolith and water-rock reactions such as serpentinization, respectively. Corresponding analogs of the martian subsurface on Earth might be the active sites of serpentinization at depths where methanogenic thermophilic archaea are the dominant species. Methanogens residing in Earth’s hydrothermal environments are usually exposed to a variety of physiological stresses including a wide range of pressures, temperatures, and pHs. Martian geochemical models imply that the pH of probable groundwater varies from 4.96 to 9.13. In this work, we used the thermophilic methanogen, Methanothermobacter wolfeii, which grows optimally at 55oC. Therefore, a temperature of 55oC was chosen for these experiments, possibly simulating Mars’ subsurface temperature. A martian geophysical model suggests depth and pressure corresponding to a temperature of 55 °C would be between 1–30 km and 100-3,000 atm respectively. Here, we have simulated Mars deep subsurface pH, pressure, and temperature conditions and have investigated the survivability, growth rate, and morphology of M. wolfeii after exposure to a wide range of pH 5–9) and pressure (1−1200 atm) at a temperature of 55 °C. Interestingly, in this study we have found that M. wolfeii was able to survive at all the pressures and pHs tested at 55 °C. In order to understand the effect of different pHs and pressures on the metabolic activities of M. wolfeii, we also calculated their growth rate by measuring methane concentration in the headspace gas samples at regular intervals. In acidic conditions, the growth rate (γ) of M. wolfeii increased with the increase in pressure. In neutral and alkaline conditions, the growth rate (γ) of M. wolfeii initially increased with pressure, but decreased upon further increase of pressure. To investigate the effect of combined pH, pressure, and temperature on the morphology of M. wolfeii, we took phase contrast images of the cells. We did not find any obvious significant alteration in the morphology of M. wolfeii cells. Methanogens, chemolithoautotrophic anaerobic microorganisms, are considered as ideal model microorganisms for Mars. In light of research presented here, we suggest that at least one methanogen, M. wolfeii, could survive in the deep subsurface environment of Mars.

A series of experiments were carried out to determine the clumped ( 13 CH 3 D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH was produced from the reaction of O( 1 D) (from O 3 photolysis) with H 2 O, and Cl was from photolysis of Cl 2 . Samples were taken from the reaction cell and analyzed for methane ( 12 CH 4 , 12 CH 3 D, 13 CH 4 , 13 CH 3 D) isotopologue ratios using tunable infrared laser direct absorption spectroscopy. Measured kinetic isotope effects for singly substituted species were consistent with previous experimental studies. For doubly substituted methane, 13 CH 3 D, the observed kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13 C and deuterium substituted species (i.e., 13,2 KIE = 13 KIE × 2 KIE). The deviation from this relationship is 0.3‰ ± 1.2‰ and 3.5‰ ± 0.7‰ for OH and Cl oxidation, respectively. This is consistent with model calculations performed using quantum chemistry and transition state theory. The OH and Cl reactions enrich the residual methane in the clumped isotopologue in open system reactions. In a closed system, however, this effect is overtaken by the large D/H isotope effect, which causes the residual methane to become anti-clumped relative to the initial methane. Based on these results, we demonstrate that oxidation of methane by OH, the predominant oxidant for tropospheric methane, will only have a minor (∼0.3‰) impact on the clumped isotope signature (Δ 13 CH 3 D, measured as a deviation from a stochastic distribution of isotopes) of tropospheric methane. This paper shows that Δ 13 CH 3 D will provide constraints on methane source strengths, and predicts that Δ 12 CH 2 D 2 can provide information on methane sink strengths.

In order to expand current atmospheric methane monitoring capabilities, we investigated the performance of an off-the-shelf, low-cost, metal oxide based methane (CH4) gas sensor. A sensor assembly was designed that powered the gas sensor and its resistive heater, provided ancillary temperature (T) and relative humidity (rH) measurements, and controlled sensor read-out and data storage. After calibrating the gas sensor with respect to methane concentration ([CH4]), T, and rH, we were able to estimate the [CH4] of lab air over a period of 31 days for a large range of T and rH conditions with a systematic error of −1.0 ppm and a variable error within ±1.7 ppm. The sensor showed no significant drift in [CH4] estimate. We show that sensor accuracy can likely be improved by optimizing the voltage regulator that powers the gas sensor’s heater, and by measuring and compensating for the difference in partial oxygen pressure of the air that was sampled during calibration and validation experiments. Such improvements are expected to allow the use of the sensor assembly for fence-line methane monitoring, for example near fossil fuel extraction sites. In its current form, the sensor assembly is suitable for detecting fugitive methane from leak-prone equipment.

Recent observations suggest that karst landscapes may be an unaccounted sink for atmospheric CH4, but questions remain about the processes contributing to sub-atmospheric CH4 mole fractions in caves. The CH4 dynamics associated with karst environments were studied over 18 months at 6 locations in Buckner Cave, Southern Indiana by measuring the mole fractions and stable isotopic composition of CH4 and carbon dioxide (CO2). CO2 mole fractions were used to infer seasonal changes in airflow. Samples were obtained on a monthly basis. CH4 mole fractions ranged from 1.9 ± 0.1 ppm near the cave entrance to 0.1 ± 0.1 ppm in the more remote parts of the cave. The carbon and hydrogen stable isotopic compositions of CH4 in the cave ranged from − 58.7 to + 7 ‰ (VPDB) and − 170 to + 10 ‰ (VSMOW), respectively. The isotopic data suggest that the CH4 dynamics of Buckner Cave can be described by a seasonally variable mixing system in which atmospheric CH4 enters primarily through the main entrance and is subsequently consumed by methanotrophs. Additionally, at least two smaller CH4 sources are evident when air has been stagnant. The results suggest that subterranean karst cavities are an important sink for atmospheric CH4.

Fugitive methane emissions from fossil fuel extraction account for significant contribution towards greenhouse gas (GHG) emissions in India. Out of total all-India GHG emissions of 1.88 million Gg-CO 2 equivalent in 2010 (with LULUCF), 48928.66 Gg-CO 2 equivalent belonged to fugitive emissions from fossil fuel extraction. Methane emission from coal mining and handling activities has increased from 0.555 Tg in 1991 to 0.765 Tg in 2012, as per national emission factors developed by CSIR-CIMFR. These estimates have been prepared as part of India's Second National Communication to the United Nations Framework Convention on Climate Change (UNFCCC) and the Biennial Update Report (BUR). With increasing demand of coal, current production is likely to touch around a billion tonnes by 2020. In this paper a time series data of coal production and associated fugitive methane emissions from coal mining and handling activities have been presented up to the year 2012. The methane released from coal mining and also coalbed methane can supplement India's scarce natural gas reserves and act as a GHG mitigation opportunity. There are several technologies to achieve this in India, which include: 1. Coalbed methane (CBM): There exists an estimated potential of 400 BCM of CBM in three provinces viz. Jharkhand, West Bengal and Chhatisgarh. Commercial scale exploitation of CBM has already begun in Raniganj Coalfield in India. 2. Coal Mine Methane (CMM): Three coalfields in the Damodar River Basin (Raniganj, Jharia and Bokaro) were studied for feasibility of recovery and utilization of CMM. Kalidaspur and Ghusick collieries in the Raniganj Coalfield, Murulidih, Amlabad, Sudamdih and Parbatpur mines in the Jharia Coalfield and Jarangdih and Sawang collieries in the East Bokaro Coalfield appear to be favourable sites for CMM recovery. 3. Ventilation Air Methane (VAM): Methane diluted by ventilating air in underground coal mines is vented to the atmosphere and may be captured for its gainful utilization. Our studies have revealed that utilization of VAM at Moonidih Mine of BCCL can lead to a net emission reduction of 0.62 million tonnes of CO 2 equivalent per year. 4. Abandoned Mine Methane (AMM): There has been no effort to quantify the potential of AMM resource in India so far. It is imperative, therefore to initiate a study for evaluation of AMM resource potential in India. Such mechanisms may serve as a valuable instrument to mitigate atmospheric methane emissions to the atmosphere and to find new pathways of clean energy deployment in India. This paper presents an analysis for policy-makers and the stake holders by providing a technological overview for augmenting clean energy resources in India.

Continuous eddy-covariance measurements of turbulent methane exchange between the ground and the atmosphere were carried out during the period from July 2013 to September 2015. The measurement sites were located in areas characterized by different types of use: the city (Łodź, central Poland) and the wetlands of Biebrza National Park (northeastern Poland). Regardless of the type of surface, such long-term, continuous measurements of the turbulent fluxes of methane are rare. Our aim was to investigate the temporal variability of the turbulent methane exchange in the surface–atmosphere system, while considering the impact of land use. Because cities are a huge source of atmospheric carbon dioxide, we compared the intensity of methane emissions from the city as compared to the wetland, which is considered to be the most intense natural source atmospheric methane. In both cases, the results show a clear prevalence of positive as compared with negative fluxes. This shows that both areas are net sources of methane to the troposphere. The measurements also demonstrated the existence of a clear annual cycle of turbulent methane flux in the centre of the city (average values in winter ranged from ∼40 to 60 nmol m−2·s−1 and were significantly greater than values measured in summer) as well as in the wetlands, where maximum values were observed during the warm part of the year (approximately 80 nmol m−2·s−1 or more). The different times of maximum CH4 flux (FCH4) occurrence resulted from the differentiation of processes that determine methane emissions: in the city these are anthropogenic emissions (strongest in winter); in the wetland, natural processes dominate. The diurnal variability of FCH4 was faintly detectable, except for the cold half of the year in the city and the warm half of the year in the wetland. The studied area of the centre of Łodź, in turn, is also characterized by a weekly cycle of methane exchange: the values measured on working days were higher by 6.6% (winter) to 5.6% (summer) than those observed on weekends. Differences in the annual exchange of methane in 2014 were insignificant: the centre of Łodź emitted 17.4 g m−2 net, while the wetland emitted about 18.7 g m−2 net. The results of the measurements performed during the period from January to September 2015, however, suggest that a very dry summer, drying of the soil and, consequently, a reduced water level in the fen significantly reduced the ability of the wetland to emit methane. This pattern was not observed in the city.

The emission of greenhouse gases (GHGs) is a major air pollution issue that affects climate change across the globe. Methane (CH 4 ), behind carbon dioxide (CO 2 ), is the second most abundant GHGs that negatively impact the atmosphere layer. Many studies have been conducted to identify a method for reducing the concentration of methane in the atmosphere. Converting methane to alternative forms source of energy, such as methanol, is a preferred method for methane reduction. This review aims to present an overview of recent literature that focuses on conversion of methane to methanol, with a focus primarily on the manufacturing systems and processes used in this conversion. Basic descriptions are given of several relevant technologies for converting methane to methanol and their characteristics, including conventional catalytic processes, plasma technology, photo-catalysts, supercritical water processes, biological processes and other processes. All of these options are feasible for use in the conversion process of methane to methanol.

Near-shore environments are a significant source of atmospheric methane but the size of this source is poorly constrained, particularly for fjords and fjards. This study investigated the methane emission rates and the drivers controlling the dynamics of dissolved methane in the Saguenay Fjord, a deep, stratified, and well‑oxygenated subarctic fjord system in eastern Canada. Dissolved methane concentrations ([CH4]) in the water column were measured in October 2016 and June, October, and November 2017, with stable carbon isotope composition of methane (δ13CCH4) analyzed during the November 2017 survey. Surface-water [CH4] ranged from 16 to 184 nmol L−1 and decreased with increasing salinity in a bi-segment linear manner, inferring a temporally constant marine endmember but a freshwater discharge-dependent river endmember. The multi-cruises dataset yields a mean [CH4] saturation ratio of 12.7 (range: 4.5–48.7) and a mean emission rate of 53.4 μmol m−2 d−1 (range: 16.4–256.9 μmol m−2 d−1). [CH4] was generally higher in surface water than in deep water. However, sill-induced mixing could homogenize [CH4] near the mouth of the fjord and sedimentary input of biogenic methane (δ13CCH4: −57.660‰) in the fjord's head region increased [CH4] in the overlying bottom water up to 459 nmol L−1. The longitudinal pattern of [CH4] below the surface layer was primarily controlled by deep-water renewal events. Deep-water [CH4] declined with rising apparent oxygen utilization, suggestive of aerobic microbial methane oxidation at rates estimated to be

Methane oxidation driven by aerobic methanotrophs plays a critical role in the alleviation of global warming. Yet, we still know little about the assembly mechanisms of methanotrophic communities and the corresponding drivers in mountain soils. Here, we comprehensively investigated methanotrophic bacteria along an elevational gradient (1800–4100 m) in Mount Gongga, China. Our results indicated that previously unrecognized AOB-rel methanotrophs predominated in mountain forest soils, and they showed distinct phylogenetic differentiation and pH preferences (pH 5.9–7.2 and pH 4.7–5.6 for AOB-rel subclade 1 and 2, respectively). Soil pH, temperature and precipitation primarily shaped methanotrophic communities. The community assembly of aerobic methanotrophs was governed mainly by deterministic processes. Our findings also implied that more acidic soils contained less phylogenetically clustered methanotrophic communities, and more neutral soils harbored more phylogenetically clustered communities. This study is the first to illustrate the significant role of soil pH in the assembly of aerobic methanotrophic communities and reinforce the importance of AOB-rel methanotrophs in atmospheric methane oxidation process in mountain forest soils.

Estimation and mapping of wetland methane (CH4) emission is carried out from the wetlands of mature Ganges deltaic environment of India. Wetlands are firstly demarcated into six types and CH4 emission is estimated for each wetland types during pre and post-monsoon seasons in order to assess seasonality effects on methanogenesis across wetland habitat types. Water Richness (WR) of the wetlands area was also assessed using Machine Learning (ML) algorithms to investigate its effect on CH4 emission. Results show significant variation of wetland CH4 emission influenced by WR and seasonality. Very high WR zone is found over almost 18% wetland area where average monthly emission is 3.0 ton/km2) covering more than 35% of the wetland area. Average monthly emission during pre-monsoon season is about 0.18 ton/km2 and which decreases to 0.15 ton/km2 during post-monsoon season. Considerable seasonal wetland areas make greater total CH4 emission during post-monsoon month than pre-monsoon. Highest average monthly emission rate is found over lakes which is 1.73 ton/km2 during pre-monsoon and reduces to 0.54 ton/km2 during post-monsoon followed by marshy wetlands. The bheries (local name of embanked wetland diurnally controlled by tidal water mainly used for pisciculture) show the lowest emission rate which is not more than 0.08 ton/km2.

The information in spectroscopic databases is routinely updated, therefore it is necessary to evaluate on a regular basis how efficient the improvements in spectroscopic data are with respect to the atmospheric remote sensing problems. One of such problems is the methane total column retrieval from the ground-based FTIR measurements of the direct solar radiation. The CH4 line parameters contained in various modern spectroscopic databases demonstrate some differences. In the present study, the impact of these differences on the atmospheric methane retrievals is estimated. The ground-based FTIR measurements at the St.Petersburg and Kourovka observational stations (Russian Federation) are taken as the basis for the study. The retrieval algorithms conform to the specifications worked out by the IRWG NDACC and TCCON networks. The databases HITRAN2001, HITRAN2008, HITRAN2012, HITRAN2016, GEISA, ATM12, ATM16, ATM19 and the GOSAT2014 line list are used as the input for the forward modeling and for the retrievals of the CH4 total column. Different criteria for quality assessment of fitting of measured and simulated transmittance spectra are considered. It has been shown that the variability of the methane total column values retrieved using absorption line parameters from different spectroscopic databases reaches 1.7%. The obtained results confirmed that for mid-infrared range the current IRWG NDACC recommendation to use HITRAN2001 is still valid: the HITRAN2001 data provide better CH4 retrievals than the newer spectroscopic databases, with the exception of one database (ATM19) yielding slightly different results but comparable to HITRAN2001. The best retrieval results in the near-infrared region are observed when the ATM, HITRAN2008 and GEISA2011 databases are used. The lowest value of RMS corresponded to the calculations which used the ATM19 line list.

To date, there has been no conclusive observation of ongoing endogenous volcanic activity on Saturn's moon Titan. However, with time, Titan's atmospheric methane is lost and must be replenished. We have modeled one possible mechanism for the replenishment of Titan's methane loss. Cryolavas can supply enough heat to release large amounts of methane from methane clathrate hydrates (MCH). The volume of methane released is controlled by the flow thickness and its areal extent. The depth of the destabilisation layer is typically ≈30% of the thickness of the lava flow (≈3 m for a 10-m thick flow). For this flow example, a maximum of 372 kg of methane is released per m2 of flow area. Such an event would release methane for nearly a year. One or two events per year covering ∼20 km2 would be sufficient to resupply atmospheric methane. A much larger effusive event covering an area of ≈9000 km2 with flows 200 m thick would release enough methane to sustain current methane concentrations for 10,000 years. The minimum size of “cryo-flows” sufficient to maintain the current atmospheric methane is small enough that their detection with current instruments (e.g., Cassini) could be challenging. We do not suggest that Titan's original atmosphere was generated by this mechanism. It is unlikely that small-scale surface MCH destabilisation is solely responsible for long-term (> a few Myr) sustenance of Titan's atmospheric methane, but rather we present it as a possible contributor to Titan's past and current atmospheric methane.

With increased concentration of methane in the atmosphere and its impact on climate, effective mitigation of methane emission is of global importance. Recent studies have shown the inhibition of microbial methanogenesis upon addition of ferruginous clay minerals. To better elucidate the mechanism of the inhibitory effect of clay minerals on methanogenesis, laboratory experiments with Methanosarcina mazei and Methanothermobacter thermautotrophicus were performed in batch systems in which pristine kaolinite or iron-coated kaolinite were added as representative clay minerals. Soluble Al in solution and production of Fe(II) and methane gas were monitored over the course of the experiments. The mineralogical changes in the kaolinites were characterized with scanning electron microscopy. The results confirmed that both Ms. mazei and Mt. thermautotrophicus were capable of reducing ferric iron with H2/CO2 as methanogenic reactants. Both pristine and iron-coated kaolinites could act as effective inhibitors of methanogenesis. The overall methane production was similar with pristine kaolinite and iron-coated kaolinite, although at the beginning of the experiment less CH4 was observed in iron-coated kaolinite system. The inhibition of methanogenic activity observed in pristine kaolinite was primarily ascribed to the toxicity effect of aluminum. A more effective inhibition of methanogenesis in iron-coated kaolinite during the first several days could be explained by the combined effects of aluminum toxicity and diversion of electron flow from CO2 to Fe(III). Our results have important implications for mitigating methane emission in natural or anthropogenic settings.

The only organic compounds that have been detected in the Martian soil are simple chlorinated compounds released from heated surface material. However, the sources of the organic carbon are in dispute. Wind abraded silicates, which are widespread on the Martian surface, can sequester atmospheric methane which generates methylated silicates and thus could provide a mechanism for accumulation of reduced carbon in the surface soil. In this study we show that thermal volatilization of methylated silicates in the presence of perchlorate leads to the production of chlorinated methane. Thus, methylated silicates could be a source of the organic carbon released as chlorinated methane upon thermal volatilization of Martian soil samples. Further, our experiments show that the ratio of the different chlorinated compounds produced is dependent on the mass ratio of perchlorate to organic carbon in the soil.

The 22/4b blowout occurred in the UK sector of the North Sea in November 1990, but during a survey in September 2011 strong gas emissions still were occurring. This manuscript summarizes the findings of the 2011 survey and subsequent studies, considering them in the context of previous investigations, and the regional geologic and oceanographic environments. The seabed crater formed during the initial event is still there, as is a previously-undiscovered secondary crater. Seabed bubble flux estimates indicate methane emission rates of 90 L s−1 at the time; however, this methane's fate(s) remains unclear. The very strong thermocline that persists for more than half the year acts as an effective barrier to upward migration, despite the presence of strong upwelling flows around the bubble plume. Clearly a large proportion of the methane is advected away from the site to be either oxidized microbially in the water column, or released to the atmosphere as a result of normal sea:air gas exchange processes. Nevertheless, a significant atmospheric methane anomaly persists in the vicinity of the blowout site. This has been constrained to likely less than 0.72 Mscfd (5 kTon yr−1) and possibly less than 0.36 Mscfd (2.5 kton yr−1). During the late-fall to early spring months (when there is no thermocline), direct methane emissions to the atmosphere are expected to increase significantly. Also, long-term monitoring has shown that periodic eruptive events occur, which likely expel great quantities of methane. These demonstrate the dynamic nature of the system and suggest that migration pathways in and between the deep sub-seabed and seabed remain active. The 22/4b Study resulted in the development and adaptation of novel techniques that are applicable to other studies of seabed seepage and the development of a number of critical hypotheses with application to megaplume seepage by natural migration pathways or from the result of anthropogenic intervention.