Increasing Methane Concentration Research Articles

Two-stage anaerobic digestion of orange peel without pre-treatment: Experimental evaluation and application to São Paulo state

Abstract Orange juice production is an important industry worldwide, specifically in Brazil, which is the leading producer. Nevertheless, approximately 50 % of the feed used for industrial production of orange juice is wasted, primarily as peels, a promising raw material for being used in the different biotechnological processes. This study evaluated the potential of two-stage anaerobic digestion (reactor of 4.3 L total volume) to valorize orange juice residues. The system replaced the use of other pretreatments and increased methane concentration (approximately 60 % compared with about 50 %) and volume (by 13 %) relative to one-stage anaerobic digestion. The accumulated biogas yield was 0.79 L/g SVT and 0.49 L/g SVT for the methanogenic and control reactors, respectively. Also, the anaerobic reactors were able to start-up with high solids feed, which could be applied to the Upflow Anaerobic Sludge Blanket (UASB) reactors currently in operation in the citrus juice industry. The potential electric power generated was estimated as 97.5 × 103 MWh/year, which might be used on-site or sold back to the energy grid where it represents 0.2 % of the total energy used by Sao Paulo State. The potential greenhouse gas mitigation from the substitution of electric energy from the Brazilian energy grid to a more renewable one from biogas burning was estimated to be 9.05 × 103 tCO2eq/year. The results demonstrated that two-stage anaerobic digestion is a promising technology for the disposal of orange peel waste while producing a useful bioenergy product.

Acoustic characteristics of cold-seep methane bubble behavior in the water column and its potential environmental impact

The amount of methane leaked from deep sea cold seeps is enormous and potentially affects the global warming, ocean acidification and global carbon cycle. It is of great significance to study the methane bubble movement and dissolution process in the water column and its output to the atmosphere. Methane bubbles produce strong acoustic impedance in water bodies, and bubble strings released from deep sea cold seeps are called “gas flares” which expressed as flame-like strong backscatter in the water column. We characterized the morphology and movement of methane bubbles released into the water using multibeam water column data at two cold seeps. The result shows that methane at site I reached 920 m water depth without passing through the top of the gas hydrate stability zone (GHSZ, 850 m), while methane bubbles at site II passed through the top of the GHSZ (597 m) and entered the non-GHSZ (above 550 m). By applying two methods on the multibeam data, the bubble rising velocity in the water column at sites I and II were estimated to be 9.6 cm/s and 24 cm/s, respectively. Bubble velocity is positively associated with water depth which is inferred to be resulted from decrease of bubble size during methane ascending in the water. Combined with numerical simulation, we concluded that formation of gas hydrate shells plays an important role in helping methane bubbles entering the upper water bodies, while other factors, including water depth, bubble velocity, initial kinetic energy and bubble size, also influence the bubble residence time in the water and the possibility of methane entering the atmosphere. We estimate that methane gas flux at these two sites is 0.4×106−87.6×106 mol/a which is extremely small compared to the total amount of methane in the ocean body, however, methane leakage might exert significant impact on the ocean acidification considering the widespread distributed cold seeps. In addition, although methane entering the atmosphere is not observed, further research is still needed to understand its potential impact on increasing methane concentration in the surface seawater and gas-water interface methane exchange rate, which consequently increase the greenhouse effect.

Effect of precursor stoichiometry on morphology, phase purity, and texture formation of hot filament CVD diamond films grown on Si (100) substrate

The effect of precursor stoichiometry is reported on morphology, phase purity, and texture formation of polycrystalline diamond films. The diamond films were deposited on 100-mm Si (100) substrates using hot filament chemical vapor deposition at substrate temperature 720–750 °C using a mixture of methane and hydrogen. The gas mixture was varied with methane concentrations 1.5% to 4.5%. Diamond film thickness and average grain size both increase with increasing methane concentration. Diamond quality was checked using surface and cross-section by ultraviolet micro-Raman spectroscopy. The data show consistent diamond properties across the surface of the film and along the cross-section. XRD pole figure analyses of the films show that 3.0% methane results in preferential orientation of diamond in the 〈111〉 direction, whereas films deposited with 4.5% methane showed texture along the 〈220〉 direction in addition to 〈111〉 which was tilted ~ 23° with respect to the surface normal.

Geochemical insights into contribution of petroleum hydrocarbons to the formation of hydrates in the Taixinan Basin, the South China Sea

Methane hydrate in the South China Sea (SCS) has extensively been considered to be biogenic on the basis of its δ13C and δD values. Although previous efforts have greatly been made, the contribution of thermogenic oil/gas has still been underestimated. In this study, biomarkers and porewater geochemical parameters in hydrate-free and hydrate-bearing sediments in the Taixinan Basin, the SCS have been measured for evaluating the contribution of petroleum hydrocarbons to the formation of hydrate deposits via a comparative study of their source inputs of organic matters, environmental conditions, and microbial activities. The results reveal the occurrence of C14–C16 branched saturated fatty acids (bSFAs) with relatively high concentrations from sulfate-reducing bacteria (SRBs) in hydrate-bearing sediments in comparison with hydrate-free sediments, which is in accord with the positive δ13C values of dissolved inorganic carbon (DIC), increasing methane concentrations, decreasing alkalinity, and concentration fluctuation of ions (Cl−, Br−, SO42−, Ca2+, and Mg2+). These data indicate the relatively active microbial activities in hydrate-bearing sediments and coincident variations of environmental conditions. Carbon isotope compositions of bSFAs (−34.0‰ to −21.2‰), n-alkanes (−34.5‰ to −29.3‰), and methane (−70.7‰ to −69.9‰) jointly demonstrate that SRBs might thrive on a different type of organic carbon rather than methane. Combining with numerous gas/oil reservoirs and hydrocarbon migration channels in the SCS, the occurrence of unresolved complex mixtures (UCMs), odd-even predominance (OEP) values (about 1.0), and biomarker patterns suggest that petroleum hydrocarbons from deep oil/gas reservoirs are the most probable carbon source. Our new results provide significant evidence that the deep oil/gas reservoirs may make a contribution to the formation of methane hydrate deposits in the SCS.

Design of methane sensor based on slow light effect in hollow core photonic crystal fiber

A tunable methane gas sensor is proposed and optimized by introducing a gas-sensitive film into the cladding air holes of hollow core photonic crystal fiber (HC-PCF). The characteristics of dispersion curve and group index of band-gap photonic crystal fiber are analyzed by the Plane Wave Expansion Method (PWM) and Finite Element Method (FEM). The results show that the micro-fluid infiltration technology can effectively improve the slow light characteristics of photonic crystal fiber (PCF), and make the central wavelength of slow-light region at the target gas absorption to discriminate the gas species. The coating technique allows the spectrum of absorption enhancement factor linearly shift with the increase of methane concentration, and the sensitivity can reach up to 0.794 nm/%. The sensor is simple and reliable with good linearity, which provides a new way for mixed gas measurements.

СВЯЗЬ МЕЖДУ ПЕРЕНОСОМ МЕТАНА В АТМОСФЕРУ И РАЗРУШЕНИЕМ ЛЕДЯНОГО ПОКРОВА КАРСКОГО МОРЯ: СПУТНИКОВЫЕ ДАННЫЕ ЗА 2003-2019 ГГ

Satellite spectrometers operating on the outgoing long-wave IR (thermal) radiation of the Earth and placed in sunsynchronous polar orbits provide a wealth of information about Arctic methane (CH4) year-round, day and night. Their data are unique for estimating methane emissions from the warming Arctic, both for land and sea. The article analyzes concentrations of methane obtained by the AIRS spectrometer in conjunction with microwave satellite measurements of sea ice concentration. The data were filtered for cases of sufficiently high temperature contrast in the lower atmosphere. The focus is on the Kara Sea during autumn-early winter season between 2003 and January 2019. This sea underwent dramatic decline in the ice cover. This shelf zone is characterized by huge reserves of oil and natural gas (~90% methane), as well as presence of sub-seabed permafrost and methane hydrates. Seasonal cycle of atmospheric methane has a minimum in early summer and a maximum in early winter. During last 16 years both summer and winter concentrations were increasing, but with different rates. Positive summer trends over the Kara Sea and over Atlantic control area were close one to another. In winter the Kara Sea methane was growing faster than over Atlantic. The methane seasonal cycle amplitude tripled from 2003 to 2019. This phenomenon was considered in terms of growing methane flux from the sea. This high trend was induced by a fast decay of the sea ice in this area with ice concentrations dropped from 95 to 20%. If the current Arctic sea cover would decline further and open water area would grow then further increase of methane concentration over the ocean may be foreseen.

Resistivity of Thin Carbon Films with Different sp-Bonds Fractions

Carbon films with different extents of sp hybridization have been grown by ion–plasma pulsed arc sputtering of graphite in a methane atmosphere. Using Raman scattering and transmission electron microscopy data, it has been shown that the content of the phase including carbon chains with sp hybridization grows with increasing methane concentration in the working volume. The resistivity of carbon films correlates well with the fraction of sp-hybridized carbon in the films.

Удельное электросопротивление тонких углеродных пленок с различной долей sp-связей

The technique of ion-plasma pulse-arc sputtering of graphite in a methane atmosphere has been employed to produce carbon films with different phase composition. Raman spectroscopy and transmission electron microscopy showed that increase of methane concentration in the vacuum deposition chamber leads to the growth of fraction containing sp-hybridized chains. In the investigated films structure, resistivity strongly correlates with the content of sp-hybridized carbon.

Combined effect of fuel injecting timing and nozzle opening pressure of a biogas-biodiesel fuelled diesel engine

Currently reduce, reuse and recycle are the three attractive options for minimizing the disposal of solid waste generated in the world; and reducing the environmental pollution. Spent tea waste (STW) and waste cooking oil (WCO) are the two different organic wastes which are disposed into open land after their usage. A continuous accumulation of these wastes may increase anthropogenic activity and result in an increase in methane concentration into the atmosphere. Previous research works report that, biogas can be obtained from STW by anaerobic digestion and biodiesel can be produced from WCO by the transesterification processes. In this research work, an attempt was made to explore the possibility of using biodiesel from WCO and biogas obtained from STW as fuels to operate a compression ignition (CI) engine on a dual fuel mode (DFM). The feed stocks WCO and STW were collected from restaurants, and hostels situated in an educational institute. For experimentation, a 4.4 kW, single cylinder, naturally aspirated, DI diesel engine run at a constant speed of 1500 rpm was converted into a DFM to operate on biodiesel-biogas. Experiments were conducted in the DFM test engine to assess the performance, emission and combustion parameters when the dual fuel engine was operated to run on three different mass flow rates of biogas, three different injection timings, and three different nozzle opening pressures. The results obtained from the experimentation were analysed, compared with the diesel operation and presented in this paper.

Effect of hydrogen concentration on CVD synthesis of graphene

The paper is devoted to the study of AP-CVD synthesis of graphene on a copper substrate. In this work, the effect of hydrogen concentration in the synthesis gas mixture on the growth of a graphene coating is studied experimentally. Two series of experiments with methane concentrations of 0.02% and 0.05% are presented. It is shown that a change in concentration of hydrogen has a nonmonotonic effect on the degree of substrate covering with graphene. This indicates that hydrogen is involved in several competing processes. One of these processes is stabilization of the edges of growing graphene domains. Another is etching of the forming graphene structures and reduction of hydrocarbon radicals on the copper substrate surface and in the bulk. It is shown that an increase in methane concentration leads to an increase in the rate of graphene crystal growth. To preserve the kinetics of graphene domain growth, it is necessary to reduce the H2/CH4 coefficient in the working mixture.

Investigation of monthly and seasonal changes of methane gas with respect to climate change using satellite data

Climate change and global warming are the biggest challenges in the current century. Methane gas is one of the most important greenhouse gases which can contribute to creating warming weather (about 19%). In this research, satellite data from GOSAT and MODIS and also climatic data of precipitation, temperature and humidity are used to analyze monthly and seasonal methane changes in 2012 to 2018 in North America. The results show that the methane gas has increased during this period and it increases from 1789 to 1824 ppb. The gas has monthly fluctuation and in October and September has the maximum concentration and in March and April has the minimum value. The relationship between the methane gas and temperature and LST is positive, and the relationship between the methane gas and NDVI, precipitation and humidity is negative. This verifies that the increase in methane concentration has significant relationship with low vegetation cover and high temperature. Therefore, conservation of vegetation cover can help to reduce the methane concentration.

Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes.

Meromictic lakes with anoxic bottom waters often have active methane cycles whereby methane is generally produced biogenically under anoxic conditions and oxidized in oxic surface waters prior to reaching the atmosphere. Lakes that contain dissolved ferrous iron in their deep waters (i.e., ferruginous) are rare, but valuable, as geochemical analogues of the conditions that dominated the Earth's oceans during the Precambrian when interactions between the iron and methane cycles could have shaped the greenhouse regulation of the planet's climate. Here, we explored controls on the methane fluxes from Brownie Lake and Canyon Lake, two ferruginous meromictic lakes that contain similar concentrations (max.>1mM) of dissolved methane in their bottom waters. The order Methanobacteriales was the dominant methanogen detected in both lakes. At Brownie Lake, methanogen abundance, an increase in methane concentration with respect to depths closer to the sediment, and isotopic data suggest methanogenesis is an active process in the anoxic water column. At Canyon Lake, methanogenesis occurred primarily in the sediment. The most abundant aerobic methane-oxidizing bacteria present in both water columns were associated with the Gammaproteobacteria, with little evidence of anaerobic methane oxidizing organisms being present or active. Direct measurements at the surface revealed a methane flux from Brownie Lake that was two orders of magnitude greater than the flux from Canyon Lake. Comparison of measured versus calculated turbulent diffusive fluxes indicates that most of the methane flux at Brownie Lake was non-diffusive. Although the turbulent diffusive methane flux at Canyon Lake was attenuated by methane oxidizing bacteria, dissolved methane was detected in the epilimnion, suggestive of lateral transport of methane from littoral sediments. These results highlight the importance of direct measurements in estimating the total methane flux from water columns, and that non-diffusive transport of methane may be important to consider from other ferruginous systems.

Formation of authigenic carbonates at a methane seep site in the middle Okinawa Trough, East China Sea

The formation of authigenic carbonates at cold seep is closely related to underlying methane seepage and anaerobic oxidation of methane (AOM), and these processes can be reflected in the geochemical characteristics of pore water in the sediments. In terms of petrological, mineralogical and geochemical analyses of research materials, including authigenic carbonates and pore water samples from the middle Okinawa Trough, East China Sea,these results show that authigenic carbonate minerals are mainly composed of high-magnesium calcite, low-magnesium calcite, dolomite, and iron dolomite and exhibit extremely negative carbon isotopic compositions (δ13C = −52.30‰ to −31.10‰ V-PDB) and positive oxygen isotopic compositions (δ18O = 3.36‰ to 7.27‰ V-PDB). Geochemical analyses of pore water suggest linear sulfate gradients and steep increase of methane and total alkalinity concentrations with depth, which indicate sulfate-induced AOM activities. Based on the sulfate concentration reduction, carbon isotope characteristics of dissolved inorganic carbon (DIC) and increased methane concentration, the sulfate-methane interface (SMI) is considered to be shallow. These data, combined with the variations in ion concentrations in pore water, suggest that the leakage of biogenic methane and intense AOM resulted in the formation of abundant authigenic carbonates, which inherited light carbon (12C)-enriched isotopic signature of methane in the shallow sediments. Combined geochemical characteristics of pore water and authigenic carbonates, intense methane seep activities and associated AOM can be inferred both in present-day and ancient geological records on the western slope of the middle Okinawa Trough.

Degradation of Lignocellulosic Complex Through Production of Struvite from Digestate

Anaerobic digestion (AD) is already contributing to global climate change efforts both from feedstock and end-use side but there is still room for an improvement. Digestate is a by-product of AD process that has been neglected during the 2000s and beyond biogas market uptake in the EU. In areas densely populated with AD plants, the same challenges occur as intensive livestock production: feedstock for AD process and lack of available land for nutrient application, in compliance with the good agriculture practice. If digestate is to become a storable fertilizer, it could also replace fossil-based fertilizer and add to GHG emission savings. This paper examines a viability of thermo-chemical digestate treatment to utilize it as feedstock in the AD process by crystalizing nutrients from digestate to allow long distance nutrient application. Digestate was treated with thermo-chemical treatment, consisted of mostly components (heat, sulphur) available on site. The treatment proved the degradation of lignocellulosic walls, allowing more access of bacteria to monosaccharides concentrations, i.e. sugars, but nutrients crystallization also occurred, producing struvite and β-calcium phosphate tetrahydrate. Treated digestate was re-circulated in AD to record an increase in methane concentrations by 3–5 vol%, compared to conventional mixtures. The results lay foundation for further research in GHG emission savings from digestate, improved nutrient cycle and digestate management as well as potential in improvement of economic feasibility of an AD plant by expanding the feedstock base to locally available plant materials with tighter lignocellulosic bonds.

Chemical structure analysis of diamond-like carbon by Raman spectroscopy

The chemical structure of diamond-like carbon (DLC) films was analyzed by Raman spectroscopy. The samples were DLC films synthesized by photoemission-assisted Townsend discharge (PATD). Group theory of the fundamental molecular structures suggested that the Raman spectrum consists of five bands with specific vibration modes, and the lineshape was represented by a modified Voigt-type formula. Analysis of the areas and positions of the bands resulted in the chemical structure of the DLC films with the sp2 cluster model. The model comprises conjugated and conductive clusters of sp2 carbons (sp2 clusters) floating in a non-conjugated and dielectric matrix of sp2 carbon, sp3 carbon, and hydrogen. The sp2 clusters were rather aliphatic for DLC films formed in low concentration of methane. The clusters grew to become aromatic with increasing methane concentration. The number of defects or dangling bonds increased similarly but were terminated with hydrogen for the films formed in a high methane concentration. The essential structure of DLC is the result of the development of random conjugation represented by the sp2 cluster model. We consider that DLC is a carbonaceous material in which conjugation increases slowly with time during the deposition process and which exhibits dielectric characteristics.

Selective Area Deposition of Hot Filament CVD Diamond on 100 mm MOCVD Grown AlGaN/GaN Wafers

A new technique is reported for selective growth of polycrystalline diamond by hot filament chemical vapor deposition (HFCVD) on AlGaN/GaN-on-Si (111) wafers without degradation of the underlying layers. Selective diamond seeding is accomplished by dispersing nanodiamond seeds in photoresist and patterned lithographically prior to HFCVD growth. A thin layer of plasma enhanced CVD SiNx, deposited prior to seeding and diamond deposition, was found to be essential to protect the AlGaN/GaN wafer. A methane concentration of 3.0% was used to achieve an increased diamond growth rate and faster surface coverage. Excellent selectivity and minimal AlGaN surface damage were achieved with increased methane concentration. Damage mitigation was confirmed by comparison of atomic force microscopy, X-ray diffraction, and Raman spectroscopy, each conducted before and after diamond deposition, and by SEM images of the final structures.

Increased methane concentration alters soil prokaryotic community structure along an artificial pH gradient

Global climate change may have a large impact on increased emission rates of carbon dioxide and methane to total greenhouse gas emissions from terrestrial wetlands. Methane consumption by soil microbiota in alpine wet meadows serves as a biofilter for the methane produced in the waterlogged soil below. Altered pH regimes change microbial community composition and structure by exerting selection pressure on soil microorganisms with different ecological strategies and thus affect greenhouse gas emissions resulting from the metabolic activity of soil microorganisms. However, responses of prokaryotic communities to artificial pH shift under elevated methane concentration remain unclear. In this study, we assessed diversity and relative abundance of soil prokaryotes in an alpine meadow under elevated methane concentration along an artificial pH gradient using laboratory incubation experiments. We established an incubation experiment treated with artificial pH gradient (pH 4.5–8.5). After 3 months of incubation, 300 ml of methane at a concentration of 20,000 ppm was added to stimulate potential methanothrophs in topsoil. Sequencing of 16S rRNA gene indicated increasing of relative abundances of Crenarchaeota, Chloroflexi, Bacteroidetes, and Planctomycetes in soil after addition of methane, while the relative abundances of Actinobacteria and Gemmatimonadetes did not significant change before and after methane treatment. Results of phylogenetic relatedness of soil prokaryotes showed that microbial community is mostly shaped by deterministic factors. Species indicator analysis revealed distinct OTUs among various pH and methane treatments. Network analysis revealed distinct co-occurrence patterns of soil prokaryotic community before and after methane addition, and different correlation patterns among various prokaryotic taxa. Linear regression model revealed significant decrease of methane oxidation along elevated pH gradient. Soil pH constituted a strong environmental filter in species assembly of soil prokaryotic community. Methane oxidation rates decreased significantly with elevated pH. The interactive effects of elevated methane concentration and pH are therefore promising topic for future research.

Multiphonon replicas in Raman spectra and conductivity properties of carbon films with different concentrations of sp1-bonds

The method of ion-plasma pulse-arc sputtering of graphite in a methane atmosphere has been employed to produce carbon films with different rate of sp1-bonds having a significant impact on the electrical conductivity of those films. Raman spectroscopy showed that the line near 2040 cm−1, corresponding to the oscillation of long carbon chains with sp1-hybridization, became more prominent with increase of methane concentration in the vacuum deposition chamber. The obtained spectra revealed multiphonon replicas of the 2040 cm−1 line that is evidently associated with the presence of defects in carbon chains.

Study on Coal Spontaneous Combustion Characteristics under Methane-Containing Atmosphere

ABSTRACTTo explore the effects of methane on the characteristics of coal spontaneous combustion, coal low-temperature oxidation and Fourier transform infrared spectroscopy experiments were conducted. The tested airflows had an oxygen–nitrogen ratio of 0.266, and methane concentrations of 0−3% by volume. Moreover, the coal oxidation characteristics and the various types and quantities of functional groups were investigated. The results show that CO/CO2 production and oxygen consumption rates were higher for coal samples under airflow atmospheres containing methane than for airflow atmospheres without methane. However, the apparent activation energy of coal samples in airflows containing methane was lower than for airflow atmosphere without methane. It is speculated that airflows with 1−3% methane concentrations have a positive impact on coal spontaneous combustion. This study used OMNIC and PeakFit v4.12 programs to analyze the effect of airflows containing methane on the functional groups of coal spontaneous combustion. The Pearson correlation coefficient method was introduced to analyze the relationship between the key functional groups and apparent activation energies of coal samples. The results indicated that the key functional groups of the coal samples below the critical temperature were methyl (−CH3) and methylene (−CH2). Above the critical temperature, aromatic C−H, methyl (−CH3), and methylene (−CH2) were the key functional groups. After reaching the cracking temperature, aromatic C−H and alkyl ether C−O−C became the key functional groups. With increasing methane concentration, aromatic C–H makes a negative contribution to coal spontaneous combustion, while methyl (−CH3) and methylene (−CH2) make positive contributions. The inhibition of alkyl ether C−O−C to coal spontaneous combustion is weakened, and the inhibition of aromatic ring C=C to coal spontaneous combustion is enhanced.

Microbial communities involved in aerobic and anaerobic methane cycling in a meromictic ferruginous subarctic lake

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 82:1-18 (2018) - DOI: https://doi.org/10.3354/ame01878 Microbial communities involved in aerobic and anaerobic methane cycling in a meromictic ferruginous subarctic lake Anna Kallistova1,*, Vitaly Kadnikov2,*, Igor Rusanov1, Natalia Kokryatskaya3, Alexey Beletsky2, Andrey Mardanov2, Alexander Savvichev1, Nikolai Ravin2, Nikolai Pimenov1,** 1Winogradsky Institute of Microbiology, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow 119071, Russia 2Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow 119071, Russia 3N. Laverov Federal Center for Integrated Arctic Research, Arkhangelsk 163000, Russia *These authors contributed equally to this work**Corresponding author: npimenov@mail.ru ABSTRACT: Since boreal lakes are now considered an important source of atmospheric methane, new information concerning the activity and diversity of methane cycle microorganisms is critical for understanding the causes of methane emission from these lakes. This study investigated the diversity of microbial communities in the water column of subarctic Lake Svetloe, belonging to a rare type of freshwater sulfate-poor meromictic basins with high concentrations of Fe2+ and methane in the permanently anoxic hypolimnion. A combination of physicochemical and radiotracer analysis, high-throughput sequencing of the 16S rRNA genes and incubation experiments was used to link microbial community profile and methane cycle processes. It was shown that methane was produced by aceticlastic Methanothrix and hydrogenotrophic Methanoregula, which were also detected in the oxygenated epilimnion, together with a small increase in methane concentration. Radiotracer analysis revealed methane oxidation (MO) in oxic and anoxic zones with 2 maxima at the chemocline. The first MO peak was attributed to aerobic Methylobacter trophically interacting with cyanobacteria, which was confirmed by obtaining light-dependent MO. The highest MO activity matched the lower chemocline layer where aerobic methanotrophs were less abundant; this suggested that other microorganisms contributed to MO together with Methylobacter. Known anaerobic methanotrophs were not detected, and incubations with Fe3+ did not reveal methane consumption under anoxic conditions. Thus, further investigations are required to determine the microorganisms and electron acceptors driving anaerobic MO. Although some questions remain open, our study may provide insight into the methane cycle microbial communities in boreal lakes. KEY WORDS: Meromictic freshwater lakes · Ferruginous lakes · Lake Svetloe · Methane cycle · Methane oxidation · Methanogenesis · 16S rRNA profiling Full text in pdf format NextCite this article as: Kallistova A, Kadnikov V, Rusanov I, Kokryatskaya N and others (2018) Microbial communities involved in aerobic and anaerobic methane cycling in a meromictic ferruginous subarctic lake. Aquat Microb Ecol 82:1-18. https://doi.org/10.3354/ame01878 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 82, No. 1. Online publication date: August 31, 2018 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2018 Inter-Research.