Biogenic Methane Production Research Articles

Tectonic Controls on Gas Hydrate Distribution Off SW Taiwan

AbstractThe northern part of the South China Sea is characterized by widespread occurrence of bottom simulating reflectors indicating the presence of marine gas hydrate. Because the area covers both a tectonically inactive passive margin and the termination of a subduction zone, the influence of tectonism on the dynamics of gas hydrate systems can be studied in this region. Geophysical data show that there are multiple thrust faults on the active margin while much fewer and smaller faults exist in the passive margin. This tectonic difference matches with a difference in the geophysical characteristics of the gas hydrate systems. High hydrate saturation derived from ocean bottom seismometer data and controlled source electromagnetic data and conspicuous high‐amplitude reflections in P‐Cable 3‐D seismic data above the bottom simulating reflector are found in the anticlinal ridges of the active margin. In contrast, all geophysical evidence for the passive margin points to normal to low hydrate saturations. Geochemical analyses of gas samples collected at seep sites on the active margin show methane with heavy δ13C isotope composition, while gas collected at the passive margin shows light carbon isotope composition. Thus, we interpret the passive margin as a typical gas hydrate province fueled by biogenic production of methane and the active margin gas hydrate system as a system that is fueled not only by biogenic gas production but also by additional advection of thermogenic methane from the subduction system.

Occurrence and fate of methane leakage from cut and buried abandoned gas wells in the Netherlands

Methane leakage caused by well integrity failure was assessed at 28 abandoned gas wells and 1 oil well in the Netherlands, which have been plugged, cut and buried to below the ground surface (≥3 mbgl). At each location, methane concentrations were thoroughly scanned at the surface. A static chamber setup was used to measure methane flow rates from the surface as well as from 1 m deep holes drilled using a hand auger. An anomalously high flow rate from 1 m depth combined with isotopic confirmation of a thermogenic origin revealed ongoing leakage at 1 of the 29 wells (3.4%), that had gone undetected by surficial measurements. Gas fluxes at the other sites were due to shallow production of biogenic methane. Detailed investigation at the leaking well (MON-02), consisting of 28 flux measurements conducted in a 2 × 2 m grid from holes drilled to 1 and 2 m depth, showed that flux magnitude was spatially heterogeneous and consistently larger at 2 m depth compared to 1 m. Isotopic evidence revealed oxidation accounted for roughly 25% of the decrease in flux towards the surface. The estimated total flux from the well (443 g CH4 hr−1) was calculated by extrapolation of the individual flow rate measurements at 2 m depth and should be considered an indicative value as the validity of the estimate using our approach requires confirmation by modelling and/or experimental studies. Together, our findings show that total methane emissions from leaking gas wells in the Netherlands are likely negligible compared to other sources of anthropogenic methane emissions (e.g. <1% of emissions from the Dutch energy sector). Furthermore, subsurface measurements greatly improve the likelihood of detecting leakage at buried abandoned wells and are therefore essential to accurately assess their greenhouse gas emissions and explosion hazards.

Impact of bioconversion on matrix strain response of coal reservoirs: Part 1-Experimental insights

The technical feasibility of commercial gas production from microbially enhanced coalbed methane (MECBM) reservoirs can be divided into two broad categories: microbial treatment procedures and reservoir suitability. At this time, studies investigating the changes in reservoir-scale properties of coal as a result of bioconversion are lacking. This paper, first of a two-part series, presents the experimental work aimed at investigating the changes in sorption-induced strain response of coal to helium and methane flooding as a result of bioconversion. The strain and its variation, critical to producing methane after bioconversion, were established for coal treated for three periods, 15, 30 and 60 days. The results indicated a softer coal post-bioconversion which, in turn, resulted in inelastic strain with initial helium injection. However, past this initial compression, the bioconverted coal behavior was similar to untreated coal during continued helium injection/depletion. Methane flooding resulted in decreased sorption-induced shrinkage post-treatment, the decrease in Langmuir pressure and volume constants becoming larger with continued treatment. The observed results were used to understand the changes in coal structure for production of biogenic coalbed methane (BCBM) from depleted CBM reservoirs, recharged with methane using the bioconversion technology. The second part presents a detailed analysis of the experimental results to evaluate the behavior and performance of BCBM reservoirs.

Direct isotopic evidence of biogenic methane production and efflux from beneath a temperate glacier

The base of glaciers and ice sheets provide environments suitable for the production of methane. High pressure conditions beneath the impermeable ‘cap’ of overlying ice promote entrapment of methane reserves that can be released to the atmosphere during ice thinning and meltwater evacuation. However, contemporary glaciers and ice sheets are rarely accounted for as methane contributors through field measurements. Here, we present direct field-based evidence of methane production and release from beneath the Icelandic glacier Sólheimajökull, where geothermal activity creates sub-oxic conditions suited to methane production and preservation along the meltwater flow path. Methane production at the glacier bed (48 tonnes per day, or 39 mM CH4 m−2 day−1), and evasion to the atmosphere from the proglacial stream (41 tonnes per day, or 32 M CH4 m−2 day−1) indicates considerable production and release to the atmosphere during the summer melt season. Isotopic signatures (−60.2‰ to −7.6‰ for δ13Cch4 and −324.3‰ to +161.1‰ for Dch4), support a biogenic signature within waters emerging from the subglacial environment. Temperate glacial methane production and release may thus be a significant and hitherto unresolved contributor of a potent greenhouse gas to the atmosphere.

Analysis of methanogens adsorption and biogas production characteristics from different coal surfaces.

The aim of this study was to examine the biogas production and the adsorption aspect of microorganism from different coals. Coal samples were obtained from Qianqiu mine and Guandi mine. Microbial populations were cultured from the coal mine drainage. After an anaerobic reaction period at about 35°C, adsorption rate was determined by the spectrophotometer, while a scanning electron microscopy was used to observe the microorganisms on the coal and the headspace methane was analyzed using gas chromatography. Results show that the coal rank and particle size serve as important factors influencing the adsorption of microorganism and biogenic methane production. With decreasing particle size, the Qianqiu coal produced a considerable adsorption rate between 75 and 79%, while the adsorption rate of Guandi coal was between 52 and 74%. Meanwhile, the density of microorganisms from the Qianqiu coal surface demonstrated a higher level of adsorption than that of Guandi coal following the scanning electron microscopy images. Additionally, Qianqiu coal produced a higher level of biogas production (391.766-629.199μmol/g) than that of Guandi coal (292.835-393.744μmol/g) and the Qianqiu coal also generated a higher concentration of methane during the incubation. When the adsorption rate decreasing, the biogas production from various pulverized coals appeared to be decreased and demonstrated a positive correlation to the adsorption rate. The results of this study suggest that the adsorption behavior of microorganisms is closely related to the effect of coal biodegradation and contributes to the biogenic methane production potential.

Regional patterns in the geochemistry of oil-field water, southern San Joaquin Valley, California, USA

Chemical and isotopic data for water co-extracted with hydrocarbons in oil and gas fields are commonly used to examine the source of the formation water and possible impacts on groundwater in areas of oil and gas development. Understanding the geochemical variability of oil-field water could help to evaluate its origin and delineate possible contamination of shallow aquifers in cases where oil-field water is released to the environment. Here we report geochemical and multiple isotope (H, C, O, Sr, Ra) data from 22 oil wells, three sources of produced water that are disposed of in injection wells, and two surface disposal ponds in four oil fields in the southern San Joaquin Valley, California (Fruitvale, Lost Hills, North and South Belridge). Correlations between Cl and δ18O, as well as other ions, and gradual increases in salinity with depth, indicate dilution of one or more saline end-members by meteoric water. The saline end-members, represented by deep samples (610 m–2621 m) in three oil-bearing zones, are characterized by NaCl composition, near-seawater Cl concentrations (median 20,000 mg/L), enriched δ18OH2O (median 3.4‰), high ammonium (up to 460 mg-N/L), and relatively high radium activity (226Ra+228Ra = 12.3 Bq/L). The deepest sample has low Na/Cl (0.74), high Ca/Mg (5.0), and low 87Sr/86Sr (0.7063), whereas the shallower samples have higher Na/Cl (0.86–1.2), Ca/Mg near 1, and higher 87Sr/86Sr (∼0.7083). The data are consistent with an original seawater source being modified by various depth and lithology dependent diagenetic processes. Dilution by meteoric water occurs naturally on the east side of the valley, and in association with water-injection activities on the west side. Meteoric-water flushing, particularly on the east side, results in lower solute concentrations (minimum total dissolved solids 2730 mg/L) and total radium (minimum 0.27 Bq/L) in oil-field water, and promotes biodegradation of dissolved organic carbon and hydrocarbon gases like propane. Acetate concentrations and δ13C of dissolved inorganic carbon indicate biogenic methane production occurs in some shallow oil zones. Natural and human processes produce substantial variability in the geochemistry of oil-field water that should be considered when evaluating mixing between oil-field waters and groundwater. The variability could result in uncertainty as to detecting the potential source and impact of oil-field water on groundwater.

Biogenic methane generation using solutions from column reactions of lignite with hydrogen peroxide

A microbial consortium associated with coal from the coal-bearing Soya Formation in the Tempoku Coalfield (northern Hokkaido, Japan) was cultivated with reaction solutions of lignite and hydrogen peroxide (H2O2) (i.e., chemically solubilized lignite) to evaluate in situ biogenic methane generation. Column experiments with H2O2 flowing through pulverized lignite achieved maximum concentrations of dissolved organic carbon, acetic acid, and formic acid of 6330, 612, and 1810 mg/L, respectively. Cultivation experiments using the above reaction solution as a substrate for methanogens produced nearly 6 cm3 CH4 per g lignite with a maximum rate of 0.14 cm3 per g per day. Pyrosequencing analysis of the microbial consortium after cultivation confirmed the presence of methanogens, such as Methanoregulaceae and Methanosarcinaceae, as the dominant archaea in the culture. The observed production of biogenic methane from a reaction solution of lignite and H2O2 under the simulated conditions indicates the potential for successful in situ microbially enhanced coalbed methane generation using H2O2.

Improving coal bioavailability for biogenic methane production via hydrogen peroxide oxidation

Hydrogen peroxide solution was used to pretreat coal samples for the purpose of improving bioavailability for methanogenesis. Crushed coals of subbituminous (PEN9-003) and medium-volatile-bituminous (C.D.) ranks were oxidized with three different dosages of H2O2 solution over four time periods (1, 4, 7, and 30 days) in the presence of UV light. Bioassays were set up using the oxidation products as the sole carbons substrates for biomethane production. To characterize the change in coal composition after oxidation, concentrations of volatile fatty acids (VFAs) and total organic carbon (TOC) in the filtered liquid sample of the pretreatment reactor were measured. The solid phase was dried and solvent-extracted with a mixture of dichloromethane and methanol. Compounds in the organic extract were analyzed using a GC–MS. H2O2 oxidation has managed to boost the biomethane yield in the subbituminous PEN9-003 coal by a maximum 10 times to 223.7 μmol/g. Production of methane was found to increase exponentially with the concentration of H2O2 relative to coal, but less significantly with pretreatment length. In contrast, the bituminous C.D. coal was barely affected by pretreatment. In addition, oxidation has considerably enhanced solubilization of PEN9-003 coal in water, with contents of VFAs and dissolved TOC surged by up to 28.2 and 22.3 times. The pretreatment has also increased the abundance of solvent-extractable matter in PEN9-003 coal. Oxygen-containing compounds, including aliphatic carboxylic acids, alcohols, ethers, ketones, and oxygenated monocyclic aliphatic and aromatic hydrocarbons were the most affected. The enrichment was due both to formation of new chemical species and an increase in the abundance of existing compounds. In comparison, oxidation of C.D. coal failed to generate any new organic species, nor did it increase the content of dissolved TOC. Biodegradation has resulted in depletion of all dissolved organic carbon, suggesting water-soluble compounds are highly bioavailable. Bioconversion of solvent-extractable matter in PEN9-003 has been improved by a maximum 29.5% upon pretreatment, while that of C.D. coal was lowered. Molecules with heterogeneous moieties, especially those that have been enriched after pretreatment demonstrated the highest bioavailability. Thermal maturation of coal from subbituminous to medium-volatile bituminous rank has been associated with a decrease in extractable matter contents, liptinite proportion, H/C ratio, elemental oxygen, heterogeneous moieties, as well as physical accessibility to microorganisms. They are thought to be responsible for the poor bioavailability and amenability of C.D. coal to H2O2 oxidation. Application of the pretreatment is only likely to be ex-situ, in which coal beneficiation waste may be used as a feed to bioreactors. The study offers a good basis for further process optimization and upscaling.

An imaging and fractal approach towards understanding reservoir scale changes in coal due to bioconversion

Microbially enhanced coalbed methane (MECBM) aims to replicate the natural process of microbial methane generation in coal under in situ conditions. Considerable work has been reported over the years to optimize the associated microbial geo-chemistry. However, there is very little insight with regards to changes in the physical structure of coal due to bioconversion, and its impact on fluid flow properties. This paper presents the result of an image and fractal-based approach used to evaluate the changes in physical properties of coal. Samples of coal treated over 30, 60 and 120 days respectively were imaged before and after bioconversion. The results revealed that coal bioconversion resulted in swelling of the coal matrix. Cleats narrower than 5 µm reduced in its width post-bioconversion. A 77% drop in the permeability of coal is expected from the obtained results. Bioconversion also resulted in separation of thin layers of coal flakes from the coal surface, serving as a potential source of fines. Fractal analysis of the images revealed a decrease in the fractal dimension post bioconversion, which is in agreement with the previously reported studies, thus corroborating the variations in sorption-trends observed due to bioconversion. Additionally, the methodology to determine the fractal dimension via two-dimensional image processing was modified to improve its accuracy, and remove the dependency of the dimension to the scale of the obtained images. Bioconversion also resulted in formation of new pores/fractures. Shorter treatment duration resulted in nanometer-scale discontinuous pores, which do not contribute to Darcian flow. Longer treatment periods resulted in sub-micron wide continuous pores. Also, few larger fractures (>5 µm wide) saw an increase in its aperture post-treatment. This opens up new avenues, such as, utilizing artificially induced fracturing techniques to enhance biogenic methane production in future.

Biogenic Methane Cycling in a Laboratory Model of an Abandoned Bituminous Coal Mine

ABSTRACTMicrobial communities in decommissioned coal mines have the potential to promote methane generation. Here, two 1 m x 10 cm diameter column bioreactors designed to mimic an abandoned coal mine were monitored for a year, with zones of methanogenesis in the bottom, saturated waters and aerobic coal degradation and methane oxidation at the top. The resilience of aerobic methanotrophs to survive periods with low methane and oxygen conditions suggests methanotrophs may be useful in decreasing atmospheric methane fugitive emissions from decommissioned mines. When biogenic methane production from coal did occur, the rate was slow, ≤ 0.073 nmol CH4/g coal/day.

Biogenic Coal-to-Methane Conversion Efficiency Decreases after Repeated Organic Amendment

Addition of organic amendments to coal-containing systems can increase the rate and extent of biogenic methane production for 60–80 days before production slows or stops. Understanding the effect of repeated amendment additions on the rate and extent of enhanced coal-dependent methane production is important if biological coal-to-methane conversion is to be enhanced on a commercial scale. Microalgal biomass was added at a concentration of 0.1 g/L to microcosms with and without coal on days 0, 76, and 117. Rates of methane production were enhanced after the initial amendment but coal-containing treatments produced successively decreasing amounts of methane with each amendment. During the first amendment period, 113% of carbon added as amendment was recovered as methane, whereas in the second and third amendment periods, 39% and 32% of carbon added as amendment was recovered as methane, respectively. Additionally, algae-amended coal treatments produced ∼38% more methane than unamended coal treatments and ∼1...

Differentiating between biogenic and thermogenic sources of natural gas in coalbed methane reservoirs from the Illinois Basin using noble gas and hydrocarbon geochemistry

Abstract While coalbed methane (CBM) is a significant source of natural gas production globally, uncertainties regarding the proportions of biogenic and thermogenic natural gas in CBM reservoirs still remain. We integrate major gases, hydrocarbon composition, hydrocarbon stable isotopes and noble gases in fluids from 20 producing CBM wells to more accurately constrain the genetic source of natural gases in the eastern Illinois Basin, USA. Previous studies have indicated primarily biogenic production of methane (&gt;99.6%) with negligible contributions from thermogenic natural gases. However, by integrating noble gases, we identify quantifiable (up to 19.2%) contributions of exogenous thermogenic gas in produced gases from the Seelyville and Springfield coal seams. Thermogenic gases are distinguished by a positive relationship between methane, ethane and helium-4, lower C 1 /C 2 +, heavier δ 13 C-CH 4 , more radiogenic noble gases ( 4 He, 21 Ne*, 40 Ar*), and lower abundances of atmospherically derived gases ( 20 Ne, 36 Ar). Biogenic gases displayed lighter δ 13 C-CH 4 , higher C 1 /C 2 +, higher levels of atmospheric gases and lower abundances of radiogenic noble gases. Our data suggest that natural gases from a deeper, exogenous thermogenic source likely migrated to the Pennsylvanian-aged coals at an unknown time and later mixed with biogenic methane diluting the geochemical signature of the thermogenic methane within the Springfield and Seelyville coal seams.

Methanogenic fermentation of lignite with carbon-bearing additives, inferred from stable carbon and hydrogen isotopes

Lignite from the Konin area (Poland) was used as a substrate for incubation experiments to evaluate its potential for simulation of biogenic methane production. Lignite was incubated with a bacterial inoculum enriched from lake sediments, mineral media, and various supplemental components for microbial life. Additives, such as acetate, methanol, glucose, nutrient broth, and yeast extract, can significantly increase methane production. At the same time, biodegradation of these additional carbon sources leads to overestimation of methane yield. In this paper, selected geochemical properties (total organic carbon content; stable isotopic composition of carbon δ13C) were analyzed in order to evaluate changes in the organic matter of fermented lignite. Stable isotope analysis of carbon and hydrogen was applied in order to identify sources of methane and carbon dioxide formation. TOC decreased in range from 1.4 to 9.6% in lignite after fermentation. The δ13C value of lignite used in the experiments (−25.2‰) decreased after incubation to values in range from −27.1 to −26.2‰. Methane yield per g of TOC (lignite + organic carbon in nutrients) ranged from 0.47 to 2.60mM/g. Glucose, acetate, and methanol significantly increased biogas production. Nutrient broth and yeast extract were not a source of organic carbon for methane formation, but their presence enhanced biogas production. Values of δ13C(CH4) and δ2H(CH4) across incubation conditions ranged from −70.2 to −24.2‰ and from −396.6 to −290.5‰, respectively. Values of δ13C(CO2) ranged from –55.2 to 45.0‰. The high level of variation of δ13C(CH4) and δ13C(CO2) suggests mixing of gases from different carbon sources during incubation, but can also be caused by mixing of metabolic modes by the microbial community. Understanding the δ2H(CH4) variation is even more difficult than the δ13C(CH4) and δ13C(CO2), since many substrates often contain exchangeable hydrogen (e.g. in water, lignite, and elements of nutrients). The combined values of δ13C(CH4) and δ13C(CO2) suggests that the dominant methanogenesis pathway in our experiments may be acetate fermentation. In biodegraded lignite, high relative concentrations of p-cresol (one of the most abundant in the sample) and n-(2-acetylphenyl)formamide were identified. These compounds are most probably lignin decomposition products, or, in the case of the latter, bacterial by-products or remnants. Organic compounds with low molecular weights, n-alkanes, and biomolecules including ferruginol, sugiol, and 6,7-dehydroferruginol, as well as amyrins and tocopherols, were preferentially degraded. The potential for methane production from lignite spiked with carbon-bearing additives is at least one magnitude lower than that from agricultural wastes. The lignite utilization as the single substrate for methanogenic fermentation is economically unprofitable. Mixing of lignite with the external substrate as biomass may be an alternative for consideration and future research.

Pilot Test of a Fermentation Tank for Producing Coal Methane through Anaerobic Fermentation

The development and utilization of clean energy has long been a focus of research. In the coal bed methane field, most coal bed biogenic methane experiments are small static sample tests in which the initial conditions are set and the process cannot be batch-fed elements and microbial strains, and the gas cannot be collected in batches. Although significant results have been achieved in the coal-to-biogenic methane conversion in China, findings are restricted to the laboratory scale. No successful commercialization of coal bed biogenic methane production has been achieved yet. This study used a large-capacity fermentation tank (5 L) to conduct biogenic methane experiments. Results were compared to those from the traditional laboratory test. The gas production rate and gas concentration were higher when the 250 mL methane test volume was increased to a 5 L fermentation volume, increasing by 20.9% and 2.3%, respectively. The inhibition effect of the liquid phase products was reduced in the large fermentation tank, and the microbial activity was extended by batch feeding trace elements (iron and nickel) and methane strains and by semi-continuous collection of the gas. However, the gas conversion rate can be increased by retaining the H2 and CO2 in the intermediate gas products in the fermentation tank. The gas production rate was increased from 17.9 to 24.6 mL/g, increasing by 37.4%. The simulation pilot test can lay a foundation for the transition from a coal bed biogenic methane laboratory static small sample test to a dynamic pilot test, optimizing the process parameters to improve the reaction efficiency and move forward to commercialization test.

Type and amount of organic amendments affect enhanced biogenic methane production from coal and microbial community structure

Slow rates of coal-to-methane conversion limit biogenic methane production from coalbeds. This study demonstrates that rates of coal-to-methane conversion can be increased by the addition of small amounts of organic amendments. Algae, cyanobacteria, yeast cells, and granulated yeast extract were tested at two concentrations (0.1 and 0.5g/L), and similar increases in total methane produced and methane production rates were observed for all amendments at a given concentration. In 0.1g/L amended systems, the amount of carbon converted to methane minus the amount produced in coal only systems exceeded the amount of carbon added in the form of amendment, suggesting enhanced coal-to-methane conversion through amendment addition. The amount of methane produced in the 0.5g/L amended systems did not exceed the amount of carbon added. While the archaeal communities did not vary significantly, the bacterial populations appeared to be strongly influenced by the presence of coal when 0.1g/L of amendment was added; at an amendment concentration of 0.5g/L the bacterial community composition appeared to be affected most strongly by the amendment type. Overall, the results suggest that small amounts of amendment are not only sufficient but possibly advantageous if faster in situ coal-to-methane production is to be promoted.

Optimization of biogenic methane production from coal

Given continuously increasing global energy needs, diversified efforts have been made to find and exploit new natural gas resources. These include coalbed methane (CBM), which represents an important global, unconventional source of natural gas. Efforts have been underway for some time to more effectively generate methane in-situ in coal plays by introduction of nutrients and/or microbial consortia. However, much is still to be learned about the limitations and environmental conditions that support microbial growth and are conducive to biogenic methane production from coal. The present investigation evaluated environmental conditions that led to increased methane production from subbituminous coal by introducing a foreign methanogenic consortium that included Methanobacterium sp. A central composite design (CCD) was used to explore a broad range of operational conditions, examine the effects of the important environmental factors, such as temperature, pH and salt concentration, and query a feasible region of operation to maximize methane production from coal. An anticipated detrimental effect of NaCl concentration on methane production was observed for the consortium assessed. The range of feasible operational conditions comprised initial pH values between 4.2 and 6.8, temperatures between 23°C and 37°C, and NaCl concentrations between 3.7mg/cm3 and 9.0mg/cm3. Coal biogasification was optimal for this consortium at an initial pH value of 5.5, at 30°C, and at a NaCl concentration 3.7mg/cm3 (i.e., 145,165ppm, which is 25.6sft3/ton).

Microbial community structure and soil pH correspond to methane production in Arctic Alaska soils.

While there is no doubt that biogenic methane production in the Arctic is an important aspect of global methane emissions, the relative roles of microbial community characteristics and soil environmental conditions in controlling Arctic methane emissions remains uncertain. Here, relevant methane-cycling microbial groups were investigated at two remote Arctic sites with respect to soil potential methane production (PMP). Percent abundances of methanogens and iron-reducing bacteria correlated with increased PMP, while methanotrophs correlated with decreased PMP. Interestingly, α-diversity of the methanogens was positively correlated with PMP, while β-diversity was unrelated to PMP. The β-diversity of the entire microbial community, however, was related to PMP. Shannon diversity was a better correlate of PMP than Simpson diversity across analyses, while rarefied species richness was a weak correlate of PMP. These results demonstrate the following: first, soil pH and microbial community structure both probably control methane production in Arctic soils. Second, there may be high functional redundancy in the methanogens with regard to methane production. Third, iron-reducing bacteria co-occur with methanogens in Arctic soils, and iron-reduction-mediated effects on methanogenesis may be controlled by α- and β-diversity. And finally, species evenness and rare species abundances may be driving relationships between microbial groups, influencing Arctic methane production.

Microbial network, phylogenetic diversity and community membership in the active layer across a permafrost thaw gradient

Biogenic production and release of methane (CH4 ) from thawing permafrost has the potential to be a strong source of radiative forcing. We investigated changes in the active layer microbial community of three sites representative of distinct permafrost thaw stages at a palsa mire in northern Sweden. The palsa site (intact permafrost and low radiative forcing signature) had a phylogenetically clustered community dominated by Acidobacteria and Proteobacteria. The bog (thawing permafrost and low radiative forcing signature) had lower alpha diversity and midrange phylogenetic clustering, characteristic of ecosystem disturbance affecting habitat filtering. Hydrogenotrophic methanogens and Acidobacteria dominated the bog shifting from palsa-like to fen-like at the waterline. The fen (no underlying permafrost, high radiative forcing signature) had the highest alpha, beta and phylogenetic diversity, was dominated by Proteobacteria and Euryarchaeota and was significantly enriched in methanogens. The Mire microbial network was modular with module cores consisting of clusters of Acidobacteria, Euryarchaeota or Xanthomonodales. Loss of underlying permafrost with associated hydrological shifts correlated to changes in microbial composition, alpha, beta and phylogenetic diversity associated with a higher radiative forcing signature. These results support the complex role of microbial interactions in mediating carbon budget changes and climate feedback in response to climate forcing.

Important Role of Fungi in the Production of Secondary Biogenic Coalbed Methane in China’s Southern Qinshui Basin

It is commonly accepted that biogenic coalbed methane (CBM) is formed by anaerobic bacteria and methanogens via coal biodegradation. While the syntrophic cooperation between fungi and methanogens has been well-established in the production of methane from rumen, little is known about the role that fungi play in the formation of biogenic CBM. Miseq sequencing and mcrA gene library were employed to investigate the fungal, archaeal, and bacterial communities in produced water from Qinshui Basin, a major site for CBM exploitation in China. The syntrophic relationship between fungi degrading coal and methanogens producing methane was also investigated. A diversity of fungal communities was found in produced water from different coal seams with the dominance of Ascomycota and Basidiomycota. Hydrogenotrophic methanogens, Methanobacterium, were also found to be predominant in produced water as revealed by Miseq sequencing and mcrA gene library analysis. Bacterial communities with potential to degrade coal were al...

The effect of bituminous coal on methanogenic mixed cultures and pure cultures of Methanococcus and Methanosarcina

In numerous global coal–bearing basins, methane, possessing a biogenic stable isotope composition, is spatially and temporally associated with groundwater recharge. However, beyond groundwater inoculating the subsurface with microorganisms, the biological mechanisms that control the distribution of biogenic methane are poorly understood. In this study, we examined the interactions between bituminous coal and a) methanogenic microbial communities sourced from the goaf of a Bowen Basin underground coal mine and b) pure cultures of methanogens. When coal mine microbial consortium was amended with acetate and a low concentration of coal (1g in 25mL medium), methane production was stimulated compared to the addition of acetate alone, though the presence of coal did not affect the methane production from H2/CO2. To test whether methanogens benefited directly from the addition of coal, 1g of either quartz sand or bituminous coal was added to a pure culture of Methanococcus maripaludis, a hydrogenotrophic methanogen isolated from the coal mine and grown on H2/CO2, and to a pure culture of Methanosarcina barkeri, an acetoclastic methanogen grown on acetate. In this experiment coal was not included as an energy source for microbial growth but to test interactions between coal and methanogens. The presence of coal in the medium did not affect methane production by Ms. barkeri but slightly inhibited methane production by M. maripaludis at the start of the growth phase. Scanning electron microscopy revealed that M. maripaludis cells were attached to both sand grains and coal particles, with preferential attachment to rough surfaces, such as cracks within broken coal pieces and clay-rich areas of coal. When the experiment with M. maripaludis and Ms. barkeri was repeated with a 1:1 volumetric ratio of bituminous coal to medium, which more accurately reflects the environmental conditions of a coal seam, methane production by M. maripaludis and Ms. barkeri was completely inhibited. In addition, M. maripaludis cell numbers declined after inoculation. This suggests that at a high coal: fluid ratio, methanogenesis is inhibited by some component of the coal, e.g., bitumens in the coal or coal-sourced hydrocarbons dissolved into the medium. Based on these laboratory results, we propose that in coal seams, the dilution of inhibitory compounds may be one mechanism by which groundwater recharge promotes biogenic methane production.