Natural Methane Research Articles

Flexible Fuel Operation of a Dry-Low-NOx Micromix Combustor with Variable Hydrogen Methane Mixtures

The role of hydrogen (H2) as a carbon-free energy carrier is discussed since decades for reducing greenhouse gas emissions. As bridge technology towards a hydrogen-based energy supply, fuel mixtures of natural gas or methane (CH4) and hydrogen are possible. The paper presents the first test results of a low-emission Micromix combustor designed for flexible-fuel operation with variable H2/CH4 mixtures. The numerical and experimental approach for considering variable fuel mixtures instead of recently investigated pure hydrogen is described. In the experimental studies, a first generation FuelFlex Micromix combustor geometry is tested at atmospheric pressure at gas turbine operating conditions corresponding to part- and full-load. The H2/CH4 fuel mixture composition is varied between 57 and 100 vol.% hydrogen content. Despite the challenges flexible-fuel operation poses onto the design of a combustion system, the evaluated FuelFlex Micromix prototype shows a significant low NOx performance and high combustion efficiency over a wide fuel range.

Микропористый углеродный материал с высокой объемной емкостью аккумулирования метана

A compacted microporous carbon material (CMC-032) was obtained, which has a number of unique properties: a high specific surface area according to BET (SBET = 2384 m2/g), a large volume of micropores (~ 0.95 cm3/g), and a very high ability to retain methane 336 m3/v3. Sorbent CMC-032 is obtained by activating polymer raw materials with potassium hydroxide and compaction by hot pressing using polyvinyl alcohol as a binder. In the most demanded range of methane accumulation pressures of 3,5 – 10,0 MPa, the amount of accumulated methane in the system with CMC-032 reaches 270 m3/m3. The amount of methane stored in the system with and without CMC-032 adsorbent at 100 bar differs by about 3 times. The physicochemical properties of the obtained CMC-032 adsorbent were studied using methods including adsorption-desorption of N2 at 77 K, X-ray diffraction analysis, FTIR spectroscopy, Raman spectroscopy, and transmission electron microscopy. Based on the adsorption characteristics, it was found that CMC-032 is a promising material for storing natural gas methane. It is assumed that the high adsorption capacity is due to the high micropore volume and packing density.

Potential Use of Seaweed (Gracilaria Tenuistipitata Var. Liui) for Reduction of Enteric Methane Emissions from Crossbred Dairy Cattle in Bangladesh

Gracilaria tenuistipitata var. Liui is a red seaweed, artificially cultivated in Nuniachara sea beach at Cox's Bazar, mostly utilized as a human diet and nutritional supplement in Bangladesh. It has certain industrial applications as well. To explore the diversified application of this seaweed in livestock feed industries to reduce enteric methane production from ruminant, a feeding trial was done at the Pranisheba R and D cattle farm, Savar, Dhaka. An ambient methane amount was measured with and without application of seaweed in concentrate feed by a sensor based IoT device of remote cowshed monitoring system. Other clinical parameters like feeding amount, body temperature, consistency of faeces was physically monitored. After proximate analysis, the composition of total crude protein, crude fiber and moisture of Gracilaria tenuistipitata var. Liui were 24.09%, 0.18%, 21.31%. The quantity of total energy was 2615 Kcal/kg. Addition of 1% seaweed to the cattle concentrated diet on a dry matter basis lowered the average ambient methane concentration from 48.30 ± 4.45 to 41.02 ± 3.41ppm, the differences were statistically significant (p<0.05). Average Body temperature, amount of daily feed intake and consistency of faeces remain unchanged. However, precise assessment of methane reduction potentiality requires a respiration chamber with an air control facility, but this observation might provide a first concept of this species as potential natural methane emissions reducer in Bangladesh.

Analytical review of technologies of the industrial development of aquatic methanohydrates

Methane hydrates are one of the most powerful reserves of unconventional sources of hydrocarbons. This is clearly evidenced by the forecast estimates of world volumes of methane in the form of gas hydrates, which many times exceed the total resources of traditional natural gas. In the foreseeable future, natural methane hydrates should significantly increase the current energy balance of natural hydrocarbon fuel resources. Progress in their study can be ensured by the dialectical unity of theoretical and experimental research, focused mainly on thermodynamics, kinetics and their physical properties, as well as on the development and testing of technologies for methane production from gas hydrate deposits. Existing methods of developing gas hydrates involve their preliminary dissociation into gas and water. At the same time, the deposit depressurization method is considered the most promising. However, there is still no commercially attractive technology for the development of gas hydrates. The article presents an overview of gas hydrate research in the world, provides an analysis of prospective methods of their development, summarizes the advantages and disadvantages of current research and industrial attempts to extract methane from aqua deposits of gas hydrates, and evaluates the prospects of various technologies. Currently known examples of research and industrial development of gas hydrate deposits have demonstrated a number of problems. However, encouraging results were obtained. The analysis of processes in the oil and gas production industry shows that profitable industrial production of natural gas from gas hydrate deposits will be possible after an effective breakthrough technology appears on the market.

Estimating 2010–2015 anthropogenic and natural methane emissions in Canada using ECCC surface and GOSAT satellite observations

Abstract. Methane emissions in Canada have both anthropogenic and natural sources. Anthropogenic emissions are estimated to be 4.1 Tg a−1 from 2010–2015 in the National Inventory Report submitted to the United Nation's Framework Convention on Climate Change (UNFCCC). Natural emissions, which are mostly due to boreal wetlands, are the largest methane source in Canada and highly uncertain, on the order of ∼ 20 Tg a−1 in biosphere process models. Aircraft studies over the last several years have provided “snapshot” emissions that conflict with inventory estimates. Here we use surface data from the Environment and Climate Change Canada (ECCC) in situ network and space-borne data from the Greenhouse Gases Observing Satellite (GOSAT) to determine 2010–2015 anthropogenic and natural methane emissions in Canada in a Bayesian inverse modelling framework. We use GEOS-Chem to simulate anthropogenic emissions comparable to the National Inventory and wetlands emissions using an ensemble of WetCHARTS v1.0 scenarios in addition to other minor natural sources. We conduct a comparative analysis of the monthly natural emissions and yearly anthropogenic emissions optimized by surface and satellite data independently. Mean 2010–2015 posterior emissions using ECCC surface data are 6.0 ± 0.4 Tg a−1 for total anthropogenic and 11.6 ± 1.2 Tg a−1 for total natural emissions. These results agree with our posterior emissions of 6.5 ± 0.7 Tg a−1 for total anthropogenic and 11.7 ± 1.2 Tg a−1 for total natural emissions using GOSAT data. The seasonal pattern of posterior natural emissions using either dataset shows slower to start emissions in the spring and a less intense peak in the summer compared to the mean of WetCHARTS scenarios. We combine ECCC and GOSAT data to characterize limitations towards sectoral and provincial-level inversions. We estimate energy + agriculture emissions to be 5.1 ± 1.0 Tg a−1, which is 59 % higher than the national inventory. We attribute 39 % higher anthropogenic emissions to Western Canada than the prior. Natural emissions are lower across Canada. Inversion results are verified against independent aircraft data and surface data, which show better agreement with posterior emissions. This study shows a readjustment of the Canadian methane budget is necessary to better match atmospheric observations with lower natural emissions partially offset by higher anthropogenic emissions.

Improving the efficiency of storage of natural and artificial methane hydrates

Methane gas hydrate is the largest hydrocarbon reservoir of natural low-carbon energy systems. Methane hydrates are a promising environmentally friendly energy source. Currently, there is a great many of experimental data on the dissociation of natural and artificial methane hydrate at negative temperatures. However, the physical mechanisms of dissociation and their description remain unclear even today, which hinders the development of these technologies. Dissociation of methane hydrates in a wide temperature range, including the self-preservation region, is studied experimentally. In this paper, experimental and theoretical studies into the natural and artificial methane hydrate dissociation are conducted. The natural gas hydrate exhibits a lower dissociation rate compared to the artificial methane hydrate. Since it is quite difficult to influence the strength of the ice crust, it is advisable to produce methane hydrate at large sphere diameters in order to reduce the dissociation rate (in the annealing temperature window). The results obtained may be useful for improving the technology of storage and transportation of natural and artificial methane hydrate.

Amazon methane budget derived from multi-year airborne observations highlights regional variations in emissions

Atmospheric methane concentrations were nearly constant between 1999 and 2006, but have been rising since by an average of ~8 ppb per year. Increases in wetland emissions, the largest natural global methane source, may be partly responsible for this rise. The scarcity of in situ atmospheric methane observations in tropical regions may be one source of large disparities between top-down and bottom-up estimates. Here we present 590 lower-troposphere vertical profiles of methane concentration from four sites across Amazonia between 2010 and 2018. We find that Amazonia emits 46.2 ± 10.3 Tg of methane per year (~8% of global emissions) with no temporal trend. Based on carbon monoxide, 17% of the sources are from biomass burning with the remainder (83%) attributable mainly to wetlands. Northwest-central Amazon emissions are nearly aseasonal, consistent with weak precipitation seasonality, while southern emissions are strongly seasonal linked to soil water seasonality. We also find a distinct east-west contrast with large fluxes in the northeast, the cause of which is currently unclear.

Conflicting estimates of natural geologic methane emissions

Global bottom-up and top-down estimates of natural, geologic methane (CH4) emissions (average approximately 45 Tg yr–1) have recently been questioned by near-zero (approximately 1.6 Tg yr–1) estimates based on measurements of 14CH4 trapped in ice cores, which imply that current fossil fuel industries’ CH4 emissions are underestimated by 25%–40%. As we show here, such a global near-zero geologic CH4 emission estimate is incompatible with multiple independent, bottom-up emission estimates from individual natural geologic seepage areas, each of which is of the order of 0.1–3 Tg yr–1. Further research is urgently needed to resolve the conundrum before rejecting either method or associated emission estimates in global CH4 accounting.

Natural gas versus methane: Ignition kinetics and detonation limit behavior in small tubes

Detonation properties of methane and natural gas were studied using ZND simulations and detonation limit experiments. The experiments were performed in two tube sizes, 32 mm and 6.4 mm in inner diameter over a range of initial pressures (between 3.4 kPa and 35 kPa) and with stoichiometric fuel-oxygen compositions. The fuels considered are high purity methane, high purity methane with dopant ozone, a real natural gas, and a family of natural gas surrogates. The natural gas surrogates were developed based on North American natural gas composition variations and designed to capture the expected mean and variance of fundamental combustion properties of natural gases. All natural gases tested in this work show a substantially smaller detonation induction length (about 40%) and lower detonation pressure limit (30% in terms of limiting pressure) than high purity methane. The ozonated methane at 3000 PPMv of ozone doping performed similarly to the natural gases. Overall, the results suggest that in methane-based mixtures, a smaller induction length correlates with a more predictable detonation behavior as evidenced by a lower detonation pressure limit. As such, natural gases are expected to have a wider operating range when used as a fuel for detonation-based engines. As importantly, induction length calculation results reveal that the variability in detonation and combustion behaviors resultant from composition variability is expected to be similar between natural gases and commercial methane. Finally, the results suggest that for safety-related studies, neat methane is a poor surrogate for studying natural gas explosions.

Natural gas methane number and its influence on the gas engine working process efficiency

The natural gas usage as a vehicle fuel in the mining industry is one of the priority tasks of the state. The article pays special attention to the component composition of natural gas from the point of view of its thermal efficiency during combustion in the combustion chamber of a power plant on a heavy-duty vehicle in difficult quarry conditions. For this, domestic and foreign methods for determining the main indicator characterizing the knock resistance of fuel in the combustion process – the methane number – are considered. Improvement of technical and economic indicators will be carried out by changing the composition of the gas mixture based on methane to fit the design features of the gas power plant, the methane number will be the determining indicator. A theoretical analysis of the influence of the methane number on such engine parameters as the compression ratio and the maximum speed of the flame front propagation in the second phase of combustion in the engine cylinder, expressed through the angle of rotation of the crankshaft, is presented. Based on the results of theoretical and experimental studies, the dependences of the influence of the methane number on the efficiency of the working process of the engine and its external speed characteristic were obtained.

Isobaric heat capacity measurements on ternary mixtures of natural gas components methane, propane and n-heptane by differential scanning calorimetry at temperatures from 197 K to 422 K and pressures up to 32 MPa

Heat capacities for single-phase mixtures of the natural gas components methane (1), propane (2) and n-heptane (3) have been determined at temperatures (197 to 421) K and pressures up to 32 MPa using two differential scanning calorimeters with a combined standard uncertainty of (2.0 to 2.6) % (k = 1). In addition, measurements were performed at pressures (0.01 to 4.40) MPa higher than saturation conditions to estimate the heat capacities of the mixtures at their bubble points. The ternary mixture data were compared with three models: the Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS), the Peng-Robinson (PR) EOS, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS incorporating group contributions. The relative deviations of the measured heat capacities from the values calculated by the three models show similar, systematic dependences on density, with larger deviations at cryogenic temperatures. The root mean square deviations from the measurements (with ideal gas heat capacity corrected) were 8.2%, 7.0% and 5.9% for the GERG-2008, PR and SAFT-γ Mie EOS, respectively. The presence of n-heptane increased the deviation up to 20% at the lowest temperature. The addition of methane to the binary mixture [0.500 C3H8 + 0.500 C7H16] was found to always increase the heat capacity. This work shows that the SAFT-γ Mie EOS can describe the single-phase measurements at above-ambient temperatures, while none of the models provides reliable predictions for cryogenic single-phase and near-bubble-point measurements.

Variability of Natural Methane Bubble Release at Southern Hydrate Ridge

AbstractCurrent estimations of seabed methane release into the ocean (0.4–48 Tg yr−1) are based on short‐term observations and implicitly assume that fluxes are constant over time. However, the intensity of gas seepage varies significantly throughout a seep lifetime. We used instruments operated by the Ocean Observatories Initiative's Regional Cabled Array to monitor variations of gas emissions over the entire Southern Hydrate Ridge summit. We show that bubble plumes emanate from distinct and persistent vents. Multiple plumes can occur within each vent and the location of their outlets may shift progressively. Active bubble plumes vary temporally in number and intensity, even within single vents. Gas emission fluctuations are partly periodic and linked to the local tide. However, short‐term variability and high ebullition events unrelated to tidal cycles are also commonly observed. Our data indicate that small‐scale processes beneath or at the sediment surface are responsible for the short‐term variability of the venting activity that is otherwise modulated by tides. Furthermore, a decrease of venting at one vent may coincide with an increase in plume activity at other vents. Our results depict a spatially and temporally dynamic seep environment, the variability of which cannot be fully characterized without systematic and comprehensive monitoring of the entire area. These results indicate that flux estimations may be largely overestimated or underestimated depending on the time, duration, and place of observation. Although sudden ebullition bursts are hardly predictable, we argue that tidal cycles must be taken into consideration when estimating gas fluxes.

ПЕРСПЕКТИВЫ ПОЛУЧЕНИЯ ГАЗОВОГО МОТОРНОГО ТОПЛИВА ИЗ БИОГАЗА АНАЭРОБНОГО СБРАЖИВАНИЯ ОТХОДОВ АПК

The ability of gas hydrates to concentrate gas into a solid chelate structure and the properties of self-preservation of gas hydrates at negative temperatures allows us to consider the possibility of developing a method for the utilization of biogas, environmentally safe storage and transportation of biomethane. (Research purpose) The research purpose is in substantiation the technological possibilities of obtaining synthetic mixed gas hydrates of biogas components, their storage and transportation based on the analysis of the existing regularities of the formation of gas hydrates in time, temperature and external pressure. (Materials and methods) The article presents the accumulated results of studies of the process of obtaining artificial hydrates of natural gas and methane- containing gas mixtures at various initial static pressures and temperatures. The object of research to substantiate the parameters of artificial creation of gas hydrates is biogas obtained during anaerobic thermophilic fermentation of organic waste at an existing experimental biogas plant. Mixed feed SK-8 with a humidity of 90-92 percent was used as an organic substrate of constant composition. The composition of biogas was studied using the Optima-7 Biogas gas analyzer. (Results and discussion) The article presents a process model and a technical appearance of an installation for producing gas motor fuel from the biogas of anaerobic digestion of organic waste of the agro-industrial complex. The hydrate formation time depends on the increase in the interfacial surface and the movement of gas bubbles relative to the liquid, which can be regulated by acting on the hydrate formation zone (shock wave, electromagnetic, mechanical, chemical, temperature). (Conclusions) The research results can be used in modeling processes in two-phase media during the formation of gas hydrates and the creation of installations for their production.

Methane oxidation to methanol over copper-containing zeolite

Methane oxidation to methanol over copper-containing zeolite

Doubly substituted isotopologues of methane hydrate (13CH3D and 12CH2D2): Implications for methane clumped isotope effects, source apportionments and global hydrate reservoirs

Recently developed methane clumped isotope techniques provides fresh and novel insights into methane biogeochemistry, which have been unobtainable through other techniques such as conventional stable isotope determinations and molecular composition measurements of hydrocarbons. Nonetheless, the governing processes and mechanisms which control the clumped isotope signatures (Δ13CH3D and Δ12CH2D2) of natural methane samples remain an active area of investigation. Here, we present paired clumped isotope measurements in methane hydrate, which is a major methane reservoir widely distributed along the continental margins and which plays an important role in the global carbon cycle and climate system. Our study aims to shed new light into the fundamental processes of methane clumped isotope effects and their potential to answer fundamental questions regarding the source and migration of methane found in naturally occurring gas hydrate accumulations.Gas hydrate samples were recovered from five shallow marine sediment sites on the eastern margin of the Japan Sea and most of them present Δ13CH3D and Δ12CH2D2 temperatures ranging from ∼15 to ∼170 °C that apparently match expected methane formation temperatures. The distribution of these clumped isotope signatures along the equilibrium line is best explained by the mixing effect of equilibrated thermogenic methane formed at temperatures of 165 ± 15 °C and biogenic methane equilibrated at 1–2 °C, which may result from slow methanogenesis, anaerobic oxidation of methane (AOM), or their combination. The influences of gas migration/diffusion, hydrate formation and dissociation on Δ13CH3D and Δ12CH2D2 values are insignificant. By combining clumped isotope results with other traditional approaches, a thermogenic and two microbial end-members as well as their isotopic compositions were identified and the relative contribution of each end-member was also quantified. The results not only demonstrate the applicability of methane clumped isotope data to identify potential end-members in natural methane samples, but also reveal that more conventional carbon isotope approaches may significantly underestimate the fraction of thermogenic methane present in global gas hydrate reservoirs. Improvements in the accuracy of source apportionment enable us to better understand the formation history and mechanisms of gas hydrate accumulation, as well as the role played by gas hydrate dissociation in past geological events. The estimated formation temperatures of thermogenic end-member can be further applied in reconstruction of the paleo geothermal gradient at the time when the thermogenic methane was formed at marine sedimentary environment.

Volumetric Mapping of Methane Concentrations at the Bush Hill Hydrocarbon Seep, Gulf of Mexico

The role of methane as a green-house gas is widely recognized and has sparked considerable efforts to quantify the contribution from natural methane sources including submarine seeps. A variety of techniques and approaches have been directed at quantifying methane fluxes from seeps from just below the sediment water interface all the way to the ocean atmosphere interface. However, there have been no systematic efforts to characterize the amount and distribution of dissolved methane around seeps. This is critical to understanding the fate of methane released from seeps and its role in the submarine environment. Here we summarize the findings of two field studies of the Bush Hill mud volcano (540 m water depth) located in the Gulf of Mexico. The studies were carried out using buoyancy driven gliders equipped with methane sensors for near real time in situ detection. One glider was equipped with an Acoustic Doppler Current Profiler (ADCP) for simultaneous measurement of currents and methane concentrations. Elevated methane concentrations in the water column were measured as far away as 2 km from the seep source and to a height of about 100 m above the seep. Maximum observed concentrations were ∼400 nM near the seep source and decreased away steadily in all directions from the source. Weak and variable currents result in nearly radially symmetric dispersal of methane from the source. The persistent presence of significant methane concentrations in the water column points to a persistent methane seepage at the seafloor, that has implications for helping stabilize exposed methane hydrates. Elevated methane concentrations in the water column, at considerable distances away from seeps potentially support a much larger methane-promoted biological system than is widely appreciated.

Metatranscriptomics reveals different features of methanogenic archaea among global vegetated coastal ecosystems

Vegetated coastal ecosystems (VCEs; i.e., mangroves, saltmarshes, and seagrasses) represent important sources of natural methane emission. Despite recent advances in the understanding of novel taxa and pathways associated with methanogenesis in these ecosystems, the key methanogenic players and the contribution of different substrates to methane formation remain elusive. Here, we systematically investigate the community and activity of methanogens using publicly available metatranscriptomes at a global scale together with our in-house metatranscriptomic dataset. Taxonomic profiling reveals that 13 groups of methanogenic archaea were transcribed in the investigated VCEs, and they were predominated by Methanosarcinales. Among these VCEs, methanogens exhibited all the three known methanogenic pathways in some mangrove sediments, where methylotrophic methanogens Methanosarcinales/Methanomassiliicoccales grew on diverse methyl compounds and coexisted with hydrogenotrophic (mainly Methanomicrobiales) and acetoclastic (mainly Methanothrix) methanogens. Contrastingly, the predominant methanogenic pathway in saltmarshes and seagrasses was constrained to methylotrophic methanogenesis. These findings reveal different archaeal methanogens in VCEs and suggest the potentially distinct methanogenesis contributions in these VCEs to the global warming.

Different names for “natural gas” influence public perception of it

In many countries, natural gas is perceived more favorably than other fossil fuels. Here, we experimentally test (N = 2931) how perceptions of natural gas vary depending on what it is called. We find that Americans have stronger positive feelings for the term “natural gas” than “natural methane gas” (d = 0.59), “fossil gas” (d = 0.80), “fracked gas” (d = 0.81), “methane” (d = 0.94), and “methane gas” (d = 0.96). Democrats and Republicans both reported more positive views of “natural gas” than “natural methane gas” or “methane [gas].” But the patterns for the two political parties differed for perceptions of “fossil gas” and “fracked gas,” which were both viewed relatively positively by Republicans but negatively by Democrats. Analyses of open-ended word associations found that many participants associated methane with words like “pollution” and “global warming,” whereas they associated natural gas with words like “clean.” The results suggest that the terms used for this fossil fuel have very different meanings among the public, which may affect people's risk perceptions, consumer choices, and support for related policies.

Atmospheric methane underestimated in future climate projections

Methane (CH4) is the second most important naturally occurring greenhouse gas (GHG) after carbon dioxide (Myhre G et al 2013 Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge: Cambridge University Press) pp 659–740). For both GHGs, the present-day budget is dominated by anthropogenic emissions (Friedlingstein P et al 2019 Earth Syst. Sci. Data 11 1783–838; Saunois M et al 2020 Earth Syst. Sci. Data 12 1561–623). For CO2 it is well established that the projected future rise in atmospheric concentration is near exclusively determined by anthropogenic emissions (Ciais P et al 2013 Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Inter-governmental Panel on Climate Change (Cambridge: Cambridge University Press) pp 465–570). For methane, this appears to be the common assumption, too, but whether this assumption is true has never been shown conclusively. Here, we investigate the evolution of atmospheric methane until 3000 CE under five Shared Socioeconomic Pathway (SSP) scenarios, for the first time using a methane-enabled state-of-the-art Earth System Model (ESM). We find that natural methane emissions, i.e. methane emissions from the biosphere, rise strongly as a reaction to climate warming, thus leading to atmospheric methane concentrations substantially higher than assumed in the scenarios used for CMIP6. We also find that the natural emissions become larger than the anthropogenic ones in most scenarios, showing that natural emissions cannot be neglected.

Candidatus Methylumidiphilus Drives Peaks in Methanotrophic Relative Abundance in Stratified Lakes and Ponds Across Northern Landscapes.

Boreal lakes and ponds produce two-thirds of the total natural methane emissions above the latitude of 50° North. These lake emissions are regulated by methanotrophs which can oxidize up to 99% of the methane produced in the sediments and the water column. Despite their importance, the diversity and distribution of the methanotrophs in lakes are still poorly understood. Here, we used shotgun metagenomic data to explore the diversity and distribution of methanotrophs in 40 oxygen-stratified water bodies in boreal and subarctic areas in Europe and North America. In our data, gammaproteobacterial methanotrophs (order Methylococcales) generally dominated the methanotrophic communities throughout the water columns. A recently discovered lineage of Methylococcales, Candidatus Methylumidiphilus, was present in all the studied water bodies and dominated the methanotrophic community in lakes with a high relative abundance of methanotrophs. Alphaproteobacterial methanotrophs were the second most abundant group of methanotrophs. In the top layer of the lakes, characterized by low CH4 concentration, their abundance could surpass that of the gammaproteobacterial methanotrophs. These results support the theory that the alphaproteobacterial methanotrophs have a high affinity for CH4 and can be considered stress-tolerant strategists. In contrast, the gammaproteobacterial methanotrophs are competitive strategists. In addition, relative abundances of anaerobic methanotrophs, Candidatus Methanoperedenaceae and Candidatus Methylomirabilis, were strongly correlated, suggesting possible co-metabolism. Our data also suggest that these anaerobic methanotrophs could be active even in the oxic layers. In non-metric multidimensional scaling, alpha- and gammaproteobacterial methanotrophs formed separate clusters based on their abundances in the samples, except for the gammaproteobacterial Candidatus Methylumidiphilus, which was separated from these two clusters. This may reflect similarities in the niche and environmental requirements of the different genera within alpha- and gammaproteobacterial methanotrophs. Our study confirms the importance of O2 and CH4 in shaping the methanotrophic communities and suggests that one variable cannot explain the diversity and distribution of the methanotrophs across lakes. Instead, we suggest that the diversity and distribution of freshwater methanotrophs are regulated by lake-specific factors.