Methane Oxidation Rates Research Articles

Microbial Abundance and Activity in Biochar-Amended Landfill Cover Soils: Evidence from Large-Scale Column and Field Experiments

AbstractField and laboratory studies were conducted to evaluate the impact of biochar amendment on methane oxidation rates and microbial communities in landfill cover soils. Deoxyribonucleic acid (...

Aerated biofilters with multiple-level air injection configurations to enhance biological treatment of methane emissions

Aiming to improve conventional methane biofilter performance, a multiple-level aeration biofilter design is proposed. Laboratory flow-through column experiments were conducted to evaluate three actively-aerated methane biofilter configurations. Columns were aerated at one, two, and three levels of the bed depth, with air introduced at flow rates calculated from methane oxidation reaction stoichiometry. Inlet methane loading rates were increased in five stages between 6 and 18mL/min. The effects of methane feeding rate, levels of aeration, and residence time on methane oxidation rates were determined. Samples collected after completion of flow-through experiments were used to determine methane oxidation kinetic parameters, Vmax, Km, and methanotrophic community distribution across biofilter columns. Results obtained from mixed variances analysis and response surfaces, as well as methanotrophic activity data, suggested that, biofilter column with two aeration levels has the most even performance over time, maintaining 85.1% average oxidation efficiency over 95days of experiments.

Mechanistic modeling of microbial interactions at pore to profile scale resolve methane emission dynamics from permafrost soil

AbstractThe sensitivity of polar regions to raising global temperatures is reflected in rapidly changing hydrological processes associated with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and stimulation of other soil‐borne greenhouse gas emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and other environmental factors. Soil structural elements such as aggregates and layering affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hot spots). We developed a mechanistic individual‐based model to quantify microbial activity dynamics in soil pore networks considering transport processes and enzymatic activity associated with methane production in soil. The model was upscaled from single aggregates to the soil profile where freezing/thawing provides macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged profile) for resolving methane production and oxidation rates. Methane transport pathways by diffusion and ebullition of bubbles vary with hydration dynamics. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability and enzyme activity) on long‐term methane emissions and carbon decomposition rates in the rapidly changing polar regions.

Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters

Abstract. Coastal seas may account for more than 75 % of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from which it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter, reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. In order to elucidate the key environmental controls, specifically the effect of oxygen availability, on MOx in a seasonally stratified and hypoxic coastal marine setting, we conducted a 2-year time-series study with measurements of MOx and physico-chemical water column parameters in a coastal inlet in the south-western Baltic Sea (Eckernförde Bay). We found that MOx rates generally increased toward the seafloor, but were not directly linked to methane concentrations. MOx exhibited a strong seasonal variability, with maximum rates (up to 11.6 nmol L−1 d−1) during summer stratification when oxygen concentrations were lowest and bottom-water temperatures were highest. Under these conditions, 2.4–19.0 times more methane was oxidized than emitted to the atmosphere, whereas about the same amount was consumed and emitted during the mixed and oxygenated periods. Laboratory experiments with manipulated oxygen concentrations in the range of 0.2–220 µmol L−1 revealed a submicromolar oxygen optimum for MOx at the study site. In contrast, the fraction of methane–carbon incorporation into the bacterial biomass (compared to the total amount of oxidized methane) was up to 38-fold higher at saturated oxygen concentrations, suggesting a different partitioning of catabolic and anabolic processes under oxygen-replete and oxygen-starved conditions, respectively. Our results underscore the importance of MOx in mitigating methane emission from coastal waters and indicate an organism-level adaptation of the water column methanotrophs to hypoxic conditions.

Rapid rates of aerobic methane oxidation at the feather edge of gas hydrate stability in the waters of Hudson Canyon, US Atlantic Margin

Aerobic oxidation is an important methane sink in seawater overlying gas seeps. Recent surveys have identified active methane seeps in the waters of Hudson Canyon, US Atlantic Margin near the updip limit of methane clathrate hydrate stability. The close proximity of these seeps to the upper stability limit of methane hydrates suggests that changing bottom water temperatures may influence the release rate of methane into the overlying water column. In order to assess the significance of aerobic methane oxidation in limiting the atmospheric expression of methane released from Hudson Canyon, the total extent of methane oxidized along with integrated oxidation rates were quantified. These calculations were performed by combining the measurements of the natural levels of methane concentrations, stable carbon isotopes, and water current velocities into kinetic isotope models yielding rates ranging from 22.8±17 to 116±76nM/day with an average of 62.7±37nM/day. Furthermore, an average of 63% of methane released into the water column from an average depth of 515m was oxidized before leaving this relatively small study area (6.5km2). Results from the kinetic isotope model were compared to previously-published but concurrently-sampled ex situ measurements of oxidation potential performed using 13C-labeled methane. Ex situ rates were substantially lower, ranging from 0.1 to 22.5nM/day with an average of 5.6±2.3nM/day, the discrepancy likely due to the inherent differences between these two techniques. Collectively, the results reveal exceptionally-rapid methane oxidation, with turnover times for methane as low as 0.3–3.7days, indicating that methane released to the water column is removed quantitatively within the greater extent of Hudson Canyon.

Annual variability and regulation of methane and sulfate fluxes in Baltic Sea estuarine sediments

Abstract. Marine methane emissions originate largely from near-shore coastal systems, but emission estimates are often not based on temporally well-resolved data or sufficient understanding of the variability of methane consumption and production processes in the underlying sediment. The objectives of our investigation were to explore the effects of seasonal temperature, changes in benthic oxygen concentration, and historical eutrophication on sediment methane concentrations and benthic fluxes at two type localities for open-water coastal versus eutrophic, estuarine sediment in the Baltic Sea. Benthic fluxes of methane and oxygen and sediment pore-water concentrations of dissolved sulfate, methane, and 35S-sulfate reduction rates were obtained over a 12-month period from April 2012 to April 2013. Benthic methane fluxes varied by factors of 5 and 12 at the offshore coastal site and the eutrophic estuarine station, respectively, ranging from 0.1 mmol m−2 d−1 in winter at an open coastal site to 2.6 mmol m−2 d−1 in late summer in the inner eutrophic estuary. Total oxygen uptake (TOU) and 35S-sulfate reduction rates (SRRs) correlated with methane fluxes showing low rates in the winter and high rates in the summer. The highest pore-water methane concentrations also varied by factors of 6 and 10 over the sampling period with the lowest values in the winter and highest values in late summer–early autumn. The highest pore-water methane concentrations were 5.7 mM a few centimeters below the sediment surface, but they never exceeded the in situ saturation concentration. Of the total sulfate reduction, 21–24 % was coupled to anaerobic methane oxidation, lowering methane concentrations below the sediment surface far below the saturation concentration. The data imply that bubble emission likely plays no or only a minor role in methane emissions in these sediments. The changes in pore-water methane concentrations over the observation period were too large to be explained by temporal changes in methane formation and methane oxidation rates due to temperature alone. Additional factors such as regional and local hydrostatic pressure changes and coastal submarine groundwater flow may also affect the vertical and lateral transport of methane.

Effect of transition metal doping on the catalytic performance of Au–Pd/3DOM Mn2O3 for the oxidation of methane and o-xylene

Palladium-based catalysts are highly active for eliminating volatile organic compounds. Reducing the use of noble metals and enhancing performance of a catalyst are always desirable. The three-dimensionally ordered macroporous (3DOM) Mn2O3-supported transition metal M (M=Mn, Cr, Fe, and Co)-doped Au–Pd nanoparticles (NPs) with an Au–Pd–xM loading of 1.86–1.97wt% were prepared using the modified polyvinyl alcohol-protected reduction method. It is found that the Au–Pd–xM NPs with a size of 3.6–4.4nm were highly dispersed on the surface of 3DOM Mn2O3. The 1.94wt% Au–Pd–0.21Co/3DOM Mn2O3 and 1.94wt% Au–Pd–0.22Fe/3DOM Mn2O3 samples performed the best for the oxidation of methane and o-xylene, respectively. The methane oxidation rate at 340°C (339.0×10−6mol/(gPds)) over 1.94wt% Au–Pd–0.21Co/3DOM Mn2O3 was three times higher than that (93.8×10−6mol/(gPds)) over 1.97wt% Au–Pd/3DOM Mn2O3, and the o-xylene reaction rate at 140°C (2.59μmol/(gNs) over 1.94wt% Au–Pd–0.22Fe/3DOM Mn2O3 was two times higher than that (0.93μmol/(gNs) over 1.97wt% Au–Pd/3DOM Mn2O3. It is concluded that doping a certain amount of the transition metal to Au–Pd/3DOM Mn2O3 could modify the microstructure of the alloy NPs, thus improving the oxygen activation and methane adsorption ability. We are sure that the M-doped Au–Pd/3DOM Mn2O3 materials are promising catalysts for the efficient removal of volatile organic compounds.

Methane cycling in a drained wetland soil profile

Peatlands have an important role in methane cycling in the natural environment. Methane emissions as a result of methanogenesis and methanotrophy in soil are affected by several environmental factors such as temperature, oxygen and groundwater level. The objective of this study was to analyse methane cycling as a function of soil depth. In this study, methane cycling and soil organic matter mineralization were investigated in a drained fen grassland area of Ljubljana marsh, Slovenia that has been subjected to reclamation strategies for several centuries. Potential mineralization, methane production and methane oxidation rates were measured in slurry incubation experiments with soil samples from 10 sampling depths of a 1-m profile. In addition, the extent of iron reduction in the soil was determined. The potential for methane production was low in the investigated soil profile, even in constantly flooded layers below the water table fluctuations. During anaerobic incubations, the highest accumulated concentrations and production rates of methane were observed in the upper 10-cm layer and the lowest in deeper soil layers, indicating that plant exudates are the main source of energy for heterotrophic soil microbes and that methanogenesis in deeper layers is limited by the availability of appropriate organic substrates. Methane oxidation was on the other hand active throughout the soil profile, suggesting that the potentially active methane oxidizing community is present despite low methane production. The highest abundance and activity of methanotrophs was detected in the water table fluctuation layers. Together, these findings have implications for understanding the biogeochemical function of drained peat soils and emphasize the influence of drainage on quality of soil organic matter and consequently on methane production even in flooded soils.

Microbial processes of the carbon and sulfur cycles in an ice-covered, iron-rich meromictic lake Svetloe (Arkhangelsk region, Russia).

Biogeochemical, isotope geochemical and microbiological investigation of Lake Svetloe (White Sea basin), a meromictic freshwater was carried out in April 2014, when ice thickness was ∼0.5 m, and the ice-covered water column contained oxygen to 23 m depth. Below, the anoxic water column contained ferrous iron (up to 240 μμM), manganese (60 μM), sulfide (up to 2 μM) and dissolved methane (960 μM). Thehighest abundance of microbial cells revealed by epifluorescence microscopy was found in the chemocline (redox zone) at 23-24.5 m. Oxygenic photosynthesis exhibited two peaks: the major one (0.43μmolCL-1 day-1 ) below the ice and the minor one inthe chemocline zone, where cyanobacteria related to Synechococcus rubescens were detected. The maximum of anoxygenic photosynthesis (0.69μmolCL-1 day-1 ) at the oxic/anoxic interface, for which green sulfur bacteria Chlorobium phaeoclathratiforme were probably responsible, exceeded the value for oxygenic photosynthesis. Bacterial sulfate reduction peaked (1.5 μmolSL-1 day-1 ) below the chemocline zone. The rates of methane oxidation were as high as 1.8 μmolCH4 L-1 day-1 at the oxi/anoxic interface and much lower in the oxic zone. Small phycoerythrin-containing Synechococcus-related cyanobacteria were probably involved in accumulation of metal oxides in the redox zone.

Methane Oxidation Prediction Curves of Soil at Different Organic Contents

The methane oxidation capacities of soil, compost, and various soilcompost mixtures at different moisture contents and temperatures were determined through a series of batch incubation experiments. The maximum methane oxidation capacities of compost and soil-compost mixtures were almost an order magnitude greater than mineral soil, as a result of increasing organic content of the media. Media with higher organic content also required much higher optimum moisture contents to achieve their maximum methane oxidation rate, with optimum moisture content for maximum methane oxidation capacity ranging between 35 and 50% of water holding capacity. The effect of temperature changes between 10°C and 30°C was found to be greater at higher organic contents. Moisture content and temperature were found to be equally important parameters for methane oxidation rate, but these effects only significantly influence oxidation rates within a range that is close to their optimum. Outside this range, methane oxidation rates fall well below their maximum and changes to moisture and temperature do not considerably affect the methane oxidation rate. The relationship between organic content and moisture content at a given temperature was developed. This curve, when combined with temperature effect can estimate methane oxidation rate at a given organic content, moisture content and temperature. Keywords: Global warming, greenhouse gas, landfill gas, methane oxidation, methanotrophic bacteria, organic contents.

Methane distribution and methane oxidation in the water column of the Elbe estuary, Germany

The River Elbe, as one of the major waterways of central Europe, is a potential source of high amounts of methane into the North Sea. Twelve sampling cruises from October 2010 until June 2013 were conducted from Hamburg towards the mouth of the Elbe at Cuxhaven. The dynamic of methane concentrations in the water column and its consumption via methane oxidizing bacteria was measured. In addition, physico-chemical parameters were used to estimate their influence on the methanotrophic activity. We observed high methane concentrations at the stations in the area of Hamburg harbour (“upper estuary”) and about 10 times lower concentrations in the lower estuary (median of 416 versus 40 nmol L−1, respectively). The methane oxidation rate mirrored the methane distribution with high values in the upper estuary and low values in the lower estuary (median of 161 versus 10 nmol L−1 day−1, respectively). Methane concentrations were significantly influenced by the river hydrology (falling water level) and the biological oxygen demand while interestingly, no clear relation to the amount of suspended particulate matter (SPM) was found. Methane oxidation rates were significantly influenced by methane concentration and to a lesser extent by temperature. Methane oxidation accounted for 41 ± 12 % of the total loss of methane in summer/fall periods, but for only 5 ± 3 % of the total loss in the winter/spring periods (total loss = methane oxidation + diffusion into the atmosphere). The average sea-air flux of methane was 33 ± 8 g CH4 m−2 y−1. We applied a box model taking into account the residence times of each water parcel depending on discharge and tidal impact. We observed almost stable methane concentrations in the lower estuary, despite a strong loss of methane through diffusion and oxidation. Thus we postulate that losses in the lower Elbe estuary were balanced by additional inputs of methane, possibly from extensive salt marshes near the river mouth.

Determining the flux of methane into Hudson Canyon at the edge of methane clathrate hydrate stability

AbstractMethane seeps were investigated in Hudson Canyon, the largest shelf‐break canyon on the northern U.S. Atlantic Margin. The seeps investigated are located at or updip of the nominal limit of methane clathrate hydrate stability. The acoustic identification of bubble streams was used to guide water column sampling in a 32 km2 region within the canyon's thalweg. By incorporating measurements of dissolved methane concentration with methane oxidation rates and current velocity into a steady state box model, the total emission of methane to the water column in this region was estimated to be 12 kmol methane per day (range: 6–24 kmol methane per day). These analyses suggest that the emitted methane is largely retained inside the canyon walls below 300 m water depth, and that it is aerobically oxidized to near completion within the larger extent of Hudson Canyon. Based on estimated methane emissions and measured oxidation rates, the oxidation of this methane to dissolved CO2 is expected to have minimal influences on seawater pH.

Atmospheric CH4 oxidation by Arctic permafrost and mineral cryosols as a function of water saturation and temperature.

The response of methanotrophic bacteria capable of oxidizing atmospheric CH4 to climate warming is poorly understood, especially for those present in Arctic mineral cryosols. The atmospheric CH4 oxidation rates were measured in microcosms incubated at 4°C and 10°C along a 1-m depth profile and over a range of water saturation conditions for mineral cryosols containing type I and type II methanotrophs from Axel Heiberg Island (AHI), Nunavut, Canada. The cryosols exhibited net consumption of ~2 ppmv CH4 under all conditions, including during anaerobic incubations. Methane oxidation rates increased with temperature and decreased with increasing water saturation and depth, exhibiting the highest rates at 10°C and 33% saturation at 5cm depth (260±60 pmol CH4 gdw-1 d-1 ). Extrapolation of the CH4 oxidation rates to the field yields net CH4 uptake fluxes ranging from 11 to 73μmol CH4 m-2 d-1 , which are comparable to field measurements. Stable isotope mass balance indicates ~50% of the oxidized CH4 is incorporated into the biomass regardless of temperature or saturation. Future atmospheric CH4 uptake rates at AHI with increasing temperatures will be determined by the interplay of increasing CH4 oxidation rates vs. water saturation and the depth to the water table during summer thaw.

Bromeliad tanks are unique habitats for microbial communities involved in methane turnover

Background and aimsTank bromeliads collect organic matter and rainwater (= tank slurry) between their densely arranged leaf axils for their nutrient demand. Diverse communities of microorganisms inhabit these tanks and are responsible for the breakdown of organic matter. Anaerobic degradation results in the release of substantial amounts of methane. We hypothesized that each individual bromeliad harbors its own microbial community, which is affected by chemical tank-slurry properties. We further hypothesized that methanotrophic bacteria inhabit bromeliad tank slurries, potentially able to oxidize the produced CH4.MethodsWe investigated communities of Bacteria, Archaea, methanogenic and methanotrophic microorganisms measuring their abundance (qPCR) and composition (TRFLP) within eight bromeliad tanks of the species Werauhia gladioliflora sampled in a Costa Rican lowland forest. Tank slurries were analyzed for pH, carbon, nitrogen, oxygen and fatty acid concentrations. Methane oxidation rates were determined in five bromeliad tank slurries.ResultsOur results showed that microbial communities differed between plants and were affected by chemical tank slurry properties. Further, not only methanogenic archaea but also methanotrophic bacteria were detected in the tanks of all bromeliad plants, the latter being potentially able to aerobically oxidize between 25 and 62 μg CH4 gdw−1 h−1.ConclusionOur results indicate that every bromeliad tank is a unique island with respect to its resident microbial community. The presence of methanogens and active methanotrophs in all tank slurries further indicates the potential for both methane formation and methane oxidation.

Microbial diversity and activity in seafloor brine lake sediments (Alaminos Canyon block 601, Gulf of Mexico).

The microbial communities thriving in deep-sea brines are sustained largely by energy rich substrates supplied through active seepage. Geochemical, microbial activity, and microbial community composition data from different habitats at a Gulf of Mexico brine lake in Alaminos Canyon revealed habitat-linked variability in geochemistry that in turn drove patterns in microbial community composition and activity. The bottom of the brine lake was the most geochemically extreme (highest salinity and nutrient concentrations) habitat and its microbial community exhibited the highest diversity and richness indices. The habitat at the upper halocline of the lake hosted the highest rates of sulfate reduction and methane oxidation, and the largest inventories of dissolved inorganic carbon, particulate organic carbon, and hydrogen sulfide. Statistical analyses indicated a significant positive correlation between the bacterial and archaeal diversity in the bottom brine sample and NH4+ inventories. Other environmental factors with positive correlation with microbial diversity indices were DOC, H2 S, and DIC concentrations. The geochemical regime of different sites within this deep seafloor extreme environment exerts a clear selective force on microbial communities and on patterns of microbial activity.

Assessment of methane generation, oxidation, and emission in a subtropical landfill test cell.

This paper presents results of a methane balance assessment in a test cell built in a region with a subtropical climate near São Paulo, Brazil. Measurements and calculations were carried out to obtain the total methane emission to the atmosphere, the methane oxidation rate in the cover, and the total methane generation rate in the test cell. The oxidation rate was obtained through a calculation scheme based on a vertical one-dimensional methane transport in the cover region. The measured maximum and mean methane fluxes to the atmosphere were 124.4 and 15.87gm(-2) d(-1), respectively. The total methane generation rate obtained for the test cell was 0.0380±0.0075mols(-1). The results yielded that 69% of the emitted methane occurred through the central well and 31% through the cover interface with the atmosphere. The evaluations of the methane oxidation fraction for localized conditions in the lateral embankment of the test cell yielded 0.36±0.11, while for the whole test cell yielded 0.15±0.10. These results conciliate localized and overall evaluations reported in the literature. The specific methane generation rate obtained for the municipal solid waste with an age of 410days was 317±62molyear(-1)ton(-1). This result from the subtropical São Paulo region is lower than reported figures for tropical climates and higher than reported figures for temperate climates.

Identification of active aerobic methanotrophs in plateau wetlands using DNA stable isotope probing.

Sedge-dominated wetlands on the Qinghai-Tibetan Plateau are methane emission centers. Methanotrophs at these sites play a role in reducing methane emissions, but relatively little is known about the composition of active methanotrophs in these wetlands. Here, we used DNA stable isotope probing to identify the key active aerobic methanotrophs in three sedge-dominated wetlands on the plateau. We found that Methylocystis species were active in two peatlands, Hongyuan and Dangxiong. Methylobacter species were found to be active only in Dangxiong peat. Hongyuan peat had the highest methane oxidation rate, and cross-feeding of carbon from methanotrophs to methylotrophic Hyphomicrobium species was observed. Owing to a low methane oxidation rate during the incubation, the labeling of methanotrophs in Maduo wetland samples was not detected. Our results indicate that there are large differences in the activity of methanotrophs in the wetlands of this region.

Activity of a Methanotrophic Consortium Isolated from Landfill Cover Soil: Response to Temperature, pH, CO2, and Porous Adsorbent

ABSTRACTA robust, naturally evolving methanotrophic community in landfill cover soil (LFCS) can be the simplest way to mitigate landfill methane emission. In this study, bacterial community composition in LFCS and methane oxidation potential of enriched methanotrophic consortium, in comparison to that of axenic Methylosinus sporium, was investigated. Growth and methane oxidation of the consortium was studied in liquid phase batch experiments under varying temperature (20–40°C), pH (5–10), headspace CO2, and in presence of porous adsorbent (1.3 cm3 sponge cubes). The 16S rRNA gene analysis revealed presence of both type-I and type-II methanotrophs along with few obligate methylotroph in LFCS. Though the optimal growth condition of the consortium was at 30°C and pH 7, it was more resilient in comparison to M. sporium. With increasing availability of porous adsorbent, methane consumption by the consortium was significantly improved (p < 0.001) reaching a maximum specific methane oxidation rate of 11.4 μmol mg−1 biomass h−1. Thus, inducing naturally thriving methanotrophs in LFCS is a better alternative to axenic methanotrophic culture in methane emission management.

Methane release from sediment seeps to the atmosphere is counteracted by highly active Methylococcaceae in the water column of deep oligotrophic Lake Constance.

Methane emissions from freshwater environments contribute substantially to global warming but are under strong control of aerobic methane-oxidizing bacteria. Recently discovered methane seeps (pockmarks) in freshwater lake sediments have the potential to bypass this control by their strong outgassing activity. Whether this is counteracted by pelagic methanotrophs is not well understood yet. We used a (3)H-CH4-radiotracer technique and pmoA-based molecular approaches to assess the activity, abundance and community structure of pelagic methanotrophs above active pockmarks in deep oligotrophic Lake Constance. Above profundal pockmarks, methane oxidation rates (up to 458 nmol CH4l(-1)d(-1)) exceeded those of the surrounding water column by two orders of magnitude and coincided with maximum methanotroph abundances of 0.6% of the microbial community. Phylogenetic analysis indicated a dominance of members of the Methylococcaceae in the water column of both, pockmark and reference sites, with most of the retrieved sequences being associated with a water-column specific clade. Communities at pockmark and reference locations also differed in parts, which was likely caused by entrainment of sediment-hosted methanotrophs at pockmark sites. Our results show that the release of seep-derived methane to the atmosphere is counteracted by a distinct methanotrophic community with a pronounced activity throughout bottom waters.

Dense bottom gravity currents and their impact on pelagic methanotrophy at oxic/anoxic transition zones

AbstractWe show that inflows of oxygenated waters into sulfidic layers have a strong impact on biogeochemical transformation at oxic/anoxic transition zones. Taking the pelagic methane dynamics in the Gotland Basin as an example, we performed our studies when one of the largest inflows ever recorded entered the Baltic Sea in March 2015. An inflowing gravity current transported oxic waters into the sulfidic deep layers and freshly generated a near‐bottom secondary redox interface. At the upper slope, where the inflowing water masses were vigorously turbulent and the main and secondary redox interfaces in close contact to each other, methane oxidation rates inside the transition zone were found to be higher compared to the weakly turbulent basin interior. At the main redox interface in the basin center, lateral intrusions of oxygenated waters into intermediate water depth may have stimulated the growth of the methanotrophic community and their activity.