Significant Source Of Methane Research Articles

High potential for CH4 emission mitigation from oil infrastructure in one of EU's major production regions

Abstract. Ambitious methane (CH4) emission mitigation represents one of the most effective opportunities to slow the rate of global warming over the next decades. The oil and gas (O&G) sector is a significant source of methane emissions, with technically feasible and cost-effective emission mitigation options. Romania, a key O&G producer within the EU, with the second highest reported annual CH4 emissions from the energy sector in the year 2020 (Greenhouse Gas Inventory Data - Comparison by Category, 2022), can play an important role towards the EU's emission reduction targets. In this study, we quantify CH4 emissions from onshore oil production sites in Romania at source and facility level using a combination of ground- and drone-based measurement techniques. Measured emissions were characterized by heavily skewed distributions, with 10 % of the sites accounting for more than 70 % of total emissions. Integrating the results from all site-level quantifications with different approaches, we derive a central estimate of 5.4 kg h−1 per site of CH4 (3.6 %–8.4 %, 95 % confidence interval) for oil production sites. This estimate represents the third highest when compared to measurement-based estimates of similar facilities from other production regions. Based on our results, we estimate a total of 120 kt CH4 yr−1 (range: 79–180 kt yr−1) from oil production sites in our studied areas in Romania. This is approximately 2.5 times higher than the reported emissions from the entire Romanian oil production sector for 2020. Based on the source-level characterization, up to three-quarters of the detected emissions from oil production sites are related to operational venting. Our results suggest that O&G production infrastructure in Romania holds a massive mitigation potential, specifically by implementing measures to capture the gas and minimize operational venting and leaks.

Greenhouse gas emissions and grain arsenic and cadmium concentrations as affected by a weed control drainage in organic rice systems

AbstractRice (Oryza sativa L.) is the primary staple food for more people than any other crop, but it is also a significant source of methane (CH4) emissions and arsenic (As) in the human diet. For organic rice, these factors pose a greater challenge due to the use of organic fertilizers and that organic rice consumers often prefer brown rice. A major management challenge for organic rice producers is weed control. In California, organic producers have developed a practice to control weeds that involves a severe dry‐down (DD) about 30 days after planting. Our objective was to determine the impact of a DD on greenhouse gas emissions and grain As and cadmium (Cd) concentrations compared to a continuously flooded (CF) control. The DD treatment reduced seasonal CH4 emissions by 50% (from 359 to 181 kg CH4 ha−1). Only during the DD period were nitrous oxide (N2O) emissions detected, but cumulative emissions were low (0.35 kg N2O ha−1). The global warming potential (GWP) was reduced by 49% in the DD treatment relative to the CF. Grain As and Cd concentrations were not at levels deemed a health concern in any treatment. However, grain As concentrations in the DD treatment were reduced by 30% and 37% in brown and white rice, respectively. Under the DD treatment, Cd concentrations increased but remained low. This study confirms that the weed management DD practice has a positive effect on GWP and grain As concentrations. In Cd contaminated soils, this practice may not be advisable.

Frequent export of pig slurry for outside storage reduced methane but not ammonia emissions in cold and warm seasons

Manure management is a significant source of methane (CH4) and ammonia (NH3), and there is an urgent need for strategies to reduce these emissions. More frequent export of manure for outside storage can lower gaseous emissions from housing facilities, but the longer residence time may then increase emissions during outside storage. This study examined CH4 and NH3 emissions from liquid pig manure (pig slurry) removed from the in-house slurry collection pits at three different frequencies, i.e., three times per week (T2.3), once per week (T7), or once after 40 days (T40, reference). The slurry from treatments T2.3 and T7 was transferred for outside storage weekly over four weeks, and slurry from treatment T40 once after 40 days, in connection with summer and winter production cycles with growing-finishing pigs. The slurry was stored in pilot-scale storage tanks with solid cover and continuous ventilation. Compared to T40, the treatments T2.3 and T7 increased CH4 emissions during outside storage, but in-house emissions were reduced even more, and the net effects on total CH4 emissions from manure management (housing unit and outside storage) were reductions of 18–41% in summer and 53–83% in winter. The frequent slurry export for outside storage led to more NH3 emissions, except for the treatment T2.3, which has slurry funnel inserts beneath the slatted floor. Measurements of in-vitro CH4 production rates suggested that shorter residence time for slurry in pig houses delayed the development of active methanogenic populations, and that this contributed to the reduction of CH4 emissions.

Elevated nutrients and surface chlorophyll-α associated with natural methane seeps in the Haima cold seep area of the Qiongdongnan Basin, northern South China Sea

Cold seeps are a significant source of methane to the ocean. However, nutrients and Chl-α in the euphotic layer overlying cold seeps have been poorly studied. Variations in Chl-α, nutrients, environmental parameters, and CH4 concentrations in the Haima cold seeps were analyzed. Results show that the overlying water exhibits a typical low nutrient and low Chl-α marine environment. Phosphate and Chl-α were significantly elevated, and the average SCM in cold seeps was much higher than that in control stations. Spearman correlation analysis indicated Chl-α in cold seep was positively correlated with salinity and negatively with nutrient and CH4 concentrations. It implied that the CH4 concentrations may promote the increase of Chl-α, and may be linked to CH4 plumes, bringing cold, nutrient-rich waters to the thermocline. However, due to the CH4 plumes hardly to track, more sampling is needed to determine the effects on Chl-α and phytoplankton in the euphotic layer.

Preparation of Mn-Doped Co3O4 Catalysts by an Eco-Friendly Solid-State Method for Catalytic Combustion of Low-Concentration Methane

Coalbed methane is a significant source of methane in the atmosphere, which is a potent greenhouse gas with a considerable contribution to global warming, thus it is of great importance to remove methane in coalbed gas before the emission. Exploring the economical non-noble metal catalysts for catalytic methane combustion (CMC) has been a wide concern to mitigate the greenhouse effect caused by the emitted low-concentration methane. Herein, a series of Mn-doped Co3O4 catalysts have been synthesized by the environmentally friendly solid-state method. As a result, the Mn0.05Co1 catalyst performed the best CMC activity (T90 = 370 °C) and good moisture tolerance (3 vol% steam). The introduction of an appropriate amount of manganese conduced Co3O4 lattice distortion and transformed Co3+ to Co2+, thus producing more active oxygen vacancies. Mn0.05Co1 exhibited better reducibility and oxygen mobility. In situ studies revealed that methane was adsorbed and oxidized much easier on Mn0.05Co1, which is the crucial reason for its superior catalytic performance.

Agriculture Residue as Bio-Cover to Inhibit Methane from Slurry Storage

Animal manure not only produces malodours, but it is also a significant source of methane (CH4) emission following a microbial-organic material breakdown. The objectives of this study were to measure methane emissions reduction following the uses of agricultural residue as biological cover on the slurry surface during the storage period. The agriculture by-products from paddy husk, rice straw, cocopeat, unfilled grains, and chipped wood were used as a physical cover on a cattle slurry surface at 30 cm thick during 90 days’ storage period. Methane emission from stored slurry was measured periodically during the storage period. All residues used were found to enhance further emission during storage thus resulting in higher methane emission compared to an uncovered slurry (Ctrl). This concludes that agriculture residues as covered materials failed to inhibit methane emission from a stored slurry.

Revolutionizing biogas generation: Polyethylene tubular digesters for household pig farms

Manure decomposition from animal waste, including farm sludge, is a significant source of methane (CH4) and carbon dioxide (CO2) emissions, aggravating global warming. Addressing this issue is vital for the environment and pivotal in achieving sustainable development goals by combating pollution from agricultural activities. One promising solution is biogas production, which offers threefold benefits including mitigation of global warming, assurance of energy security, and efficient waste management. This can be achieved by optimizing the process using substrates that yield high biogas output while ensuring low water usage and retention. This study focuses on pig farms' biogas potential of liquid and solid manure fractions performed with laboratory-scale batch digesters and enhanced polyethylene tubular digesters for evaluation. From the screening system, the biogas output from pig slurry resulted in CH4 and CO2 in 45 days, achieving 61.44 and 36.35%, respectively. After the initial screening experiment, polyethylene tubular digesters were implemented for biogas production at household pig farms and produced through fermentation in polyethylene tubular digesters under anaerobic conditions and are mainly composed of CH4 (60–64%) and CO2 (29–38%). This study suggested that the pig slurry could be a reliable biomass energy source for biogas and applicable to householders.

Ammonia and methane emissions from dairy concentrated animal feeding operations in California, using mobile optical remote sensing

Dairy concentrated animal feeding operations (CAFOs) are significant sources of methane (CH4) and ammonia (NH3) emissions in the San Joaquin Valley, California. Optical techniques, namely, remote sensing by Solar Occultation Flux (SOF) and Mobile extractive FTIR (MeFTIR), were used to measure NH3 air column and ground air concentrations of NH3 and CH4, respectively. Campaigns were performed in May and October 2019 and covered 14 dairies located near Bakersfield and Tulare, California. NH3 and CH4 emission rates from single CAFOs averaged 101.9 ± 40.6 kgNH3/h and 437.7 ± 202.0 kgCH4/h, respectively, corresponding to emission factors (EFs) per livestock unit of 9.1 ± 2.7 gNH3/LU/h and 40.1 ± 17.8 gCH4/LU/h.The NH3 emissions had a median standard uncertainty of 17% and an expanded uncertainty (95% Confidence Interval (CI)) of 37%; meanwhile, CH4 emissions estimates had greater uncertainty, median of 25% and 53% (in the 95% CI). Decreasing NH3 to CH4 ratios and NH3 EFs from early afternoon (13:00) to early night (19:00) indicated a diurnal emission pattern with lower ammonia emissions during the night. On average, measured NH3 emissions were 28% higher when compared to daytime emission rates reported in the National Emissions Inventory (NEI) and modeled according to diurnal variation. Measured CH4 emissions were 60% higher than the rates reported in the California Air Resources Board (CARB) inventory. However, comparison with airborne measurements showed similar emission rates. This study demonstrates new air measurement methods, which can be used to quantify emissions over large areas with high spatial resolution and in a relatively short time period. These techniques bridge the gap between satellites and individual CAFOs measurements.

Effects of brackish water inflow on methane-cycling microbial communities in a freshwater rewetted coastal fen

Abstract. Rewetted peatlands can be a significant source of methane (CH4), but in coastal ecosystems, input of sulfate-rich seawater could potentially mitigate these emissions. The presence of sulfate as an electron acceptor during organic matter decomposition is known to suppress methanogenesis by favoring the growth of sulfate reducers, which outcompete methanogens for substrate. We investigated the effects of a brackish water inflow on the microbial communities relative to CH4 production–consumption dynamics in a freshwater rewetted fen at the southern Baltic Sea coast after a storm surge in January 2019 and analyzed our data in context with the previous freshwater rewetted state (2014 serves as our baseline) and the conditions after a severe drought in 2018 (Fig. 1). We took peat cores at four previously sampled locations along a brackishness gradient to compare soil and pore water geochemistry as well as the microbial methane- and sulfate-cycling communities with the previous conditions. We used high-throughput sequencing and quantitative polymerase chain reaction (qPCR) to characterize pools of DNA and RNA targeting total and putatively active bacteria and archaea. Furthermore, we measured CH4 fluxes along the gradient and determined the concentrations and isotopic signatures of trace gases in the peat. We found that both the inflow effect of brackish water and the preceding drought increased the sulfate availability in the surface and pore water. Nevertheless, peat soil CH4 concentrations and the 13C compositions of CH4 and total dissolved inorganic carbon (DIC) indicated ongoing methanogenesis and little methane oxidation. Accordingly, we did not observe a decrease in absolute methanogenic archaea abundance or a substantial change in methanogenic community composition following the inflow but found that the methanogenic community had mainly changed during the preceding drought. In contrast, absolute abundances of aerobic methanotrophic bacteria decreased back to their pre-drought level after the inflow, while they had increased during the drought year. In line with the higher sulfate concentrations, the absolute abundances of sulfate-reducing bacteria (SRB) increased – as expected – by almost 3 orders of magnitude compared to the freshwater state and also exceeded abundances recorded during the drought by over 2 orders of magnitude. Against our expectations, methanotrophic archaea (ANME), capable of sulfate-mediated anaerobic methane oxidation, did not increase in abundance after the brackish water inflow. Altogether, we could find no microbial evidence for hampered methane production or increased methane consumption in the peat soil after the brackish water inflow. Because Koebsch et al. (2020) reported a new minimum in CH4 fluxes at this site since rewetting of the site in 2009, methane oxidation may, however, take place in the water column above the peat soil or in the loose organic litter on the ground. This highlights the importance of considering all compartments across the peat–water–atmosphere continuum to develop an in-depth understanding of inflow events in rewetted peatlands. We propose that the changes in microbial communities and greenhouse gas (GHG) fluxes relative to the previous freshwater rewetting state cannot be explained with the brackish water inflow alone but were potentially reinforced by a biogeochemical legacy effect of the preceding drought.

Drivers of Global Methane Emissions Embodied in International Beef Trade.

Increasing worldwide demand for beef products promotes international beef trade. Cattle raising and beef products as significant sources of methane (CH4) emissions have received widespread concerns. However, the factors driving CH4 emissions embodied in the global beef trade have not been quantified. Here, we evaluate international beef trade-induced CH4 emissions and assess the contribution of the five driving factors to changes in CH4 emissions embodied in the beef trade from 2000 to 2018. We show that driven by increasing population and meat demands, the global beef trade-induced CH4 emissions increased continuously in the past two decades, with total emissions of 9337.3 Gg in 2018. The drivers that could potentially reduce trade-related emissions are emission intensities in beef exporting countries and beef importing countries' selections of their beef suppliers. Together, these two driving factors reduced CH4 emissions by 923.5 Gg from 2012 to 2018. Results suggest that efforts should be made to reduce the emission intensity via improving cattle feed and feeding practices in beef exporting countries. Beef importing countries could also contribute to CH4 emission reduction by selecting those beef exporting countries with low emission intensities.

Quantification and assessment of methane emissions from offshore oil and gas facilities on the Norwegian continental shelf

Abstract. The oil and gas (O&G) sector is a significant source of methane (CH4) emissions. Quantifying these emissions remains challenging, with many studies highlighting discrepancies between measurements and inventory-based estimates. In this study, we present CH4 emission fluxes from 21 offshore O&G facilities collected in 10 O&G fields over two regions of the Norwegian continental shelf in 2019. Emissions of CH4 derived from measurements during 13 aircraft surveys were found to range from 2.6 to 1200 t yr−1 (with a mean of 211 t yr−1 across all 21 facilities). Comparing this with aggregated operator-reported facility emissions for 2019, we found excellent agreement (within 1σ uncertainty), with mean aircraft-measured fluxes only 16 % lower than those reported by operators. We also compared aircraft-derived fluxes with facility fluxes extracted from a global gridded fossil fuel CH4 emission inventory compiled for 2016. We found that the measured emissions were 42 % larger than the inventory for the area covered by this study, for the 21 facilities surveyed (in aggregate). We interpret this large discrepancy not to reflect a systematic error in the operator-reported emissions, which agree with measurements, but rather the representativity of the global inventory due to the methodology used to construct it and the fact that the inventory was compiled for 2016 (and thus not representative of emissions in 2019). This highlights the need for timely and up-to-date inventories for use in research and policy. The variable nature of CH4 emissions from individual facilities requires knowledge of facility operational status during measurements for data to be useful in prioritising targeted emission mitigation solutions. Future surveys of individual facilities would benefit from knowledge of facility operational status over time. Field-specific aggregated emissions (and uncertainty statistics), as presented here for the Norwegian Sea, can be meaningfully estimated from intensive aircraft surveys. However, field-specific estimates cannot be reliably extrapolated to other production fields without their own tailored surveys, which would need to capture a range of facility designs, oil and gas production volumes, and facility ages. For year-on-year comparison to annually updated inventories and regulatory emission reporting, analogous annual surveys would be needed for meaningful top-down validation. In summary, this study demonstrates the importance and accuracy of detailed, facility-level emission accounting and reporting by operators and the use of airborne measurement approaches to validate bottom-up accounting.

Using the inverse dispersion method to determine methane emissions from biogas plants and wastewater treatment plants with complex source configurations

Wastewater treatment plants (WWTPs) and biogas plants (BGPs) are significant sources of methane (CH4), with a combined share of around 40% within the waste sector of the Swiss national emission inventory. We conducted whole-plant CH4 emission measurements at two WWTPs and four agricultural BGPs in Switzerland using the inverse dispersion method (IDM). This involved open-path concentration measurements up- and downwind of the plant in combination with a backward Lagrangian stochastic (bLS) model. WWTPs in particular consist of multiple CH4 sources with different areas and emission strengths. For the combination of the individual emission sources in the bLS modelling, three different calculation approaches with different levels of detail were applied: (i) single source over enveloping polygon area, (ii) uniform emission density for all individual source areas, (iii) specified relative weighting of individual sources based on literature data. Average CH4 emissions for WWTP-1 and WWTP-2 were 0.82 kg h−1 and 0.61 kg h−1 and scaled to population equivalents (PE) 166 g PE−1 y−1 and 381 g PE−1 y−1, respectively. BGPs CH4 emissions varied between 0.39 kg h−1 and 2.22 kg h−1, corresponding to less than 5% of the plants’ CH4 production. The highest numbers were due to measurements during other than normal operating conditions. The emissions of WWTPs and BGPs comply with literature values. Approach (iii) with source weighting led to a difference of up to 43% for the two WWTPs compared to the assumption of uniform emissions. Furthermore, we demonstrate how multiple open-path concentration measurements can be combined and how the measurements can be corrected for nearby external CH4 sources not belonging to the investigated plants. The results of the present study contribute to improved emission data from the waste sector.

Airborne quantification of net methane and carbon dioxide fluxes from European Arctic wetlands in Summer 2019.

Arctic wetlands and surrounding ecosystems are both a significant source of methane (CH4) and a sink of carbon dioxide (CO2) during summer months. However, precise quantification of this regional CH4 source and CO2 sink remains poorly characterized. A research flight using the UK Facility for Airborne Atmospheric Measurement was conducted in July 2019 over an area (approx. 78 000 km2) of mixed peatland and forest in northern Sweden and Finland. Area-averaged fluxes of CH4 and carbon dioxide were calculated using an aircraft mass balance approach. Net CH4 fluxes normalized to wetland area ranged between 5.93 ± 1.87 mg m−2 h−1 and 4.44 ± 0.64 mg m−2 h−1 (largest to smallest) over the region with a meridional gradient across three discrete areas enclosed by the flight survey. From largest to smallest, net CO2 sinks ranged between −513 ± 74 mg m−2 h−1 and −284 ± 89 mg m−2 h−1 and result from net uptake of CO2 by vegetation and soils in the biosphere. A clear gradient of decreasing bulk and area-averaged CH4 flux was identified from north to south across the study region, correlated with decreasing peat bog land area from north to south identified from CORINE land cover classifications. While N2O mole fraction was measured, no discernible gradient was measured over the flight track, but a minimum flux threshold using this mass balance method was calculated. Bulk (total area) CH4 fluxes determined via mass balance were compared with area-weighted upscaled chamber fluxes from the same study area and were found to agree well within measurement uncertainty. The mass balance CH4 fluxes were found to be significantly higher than the CH4 fluxes reported by many land-surface process models compiled as part of the Global Carbon Project. There was high variability in both flux distribution and magnitude between the individual models. This further supports previous studies that suggest that land-surface models are currently ill-equipped to accurately capture carbon fluxes inthe region.This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Non-flooded riparian Amazon trees are a regionally significant methane source.

Inundation-adapted trees were recently established as the dominant egress pathway for soil-produced methane (CH4) in forested wetlands. This raises the possibility that CH4 produced deep within the soil column can vent to the atmosphere via tree roots even when the water table (WT) is below the surface. If correct, this would challenge modelling efforts where inundation often defines the spatial extent of ecosystem CH4 production and emission. Here, we examine CH4 exchange on tree, soil and aquatic surfaces in forest experiencing a dynamic WT at three floodplain locations spanning the Amazon basin at four hydrologically distinct times from April 2017 to January 2018. Tree stem emissions were orders of magnitude larger than from soil or aquatic surface emissions and exhibited a strong relationship to WT depth below the surface (less than 0). We estimate that Amazon riparian floodplain margins with a WT < 0 contribute 2.2–3.6 Tg CH4 yr−1 to the atmosphere in addition to inundated tree emissions of approximately 12.7–21.1 Tg CH4 yr−1. Applying our approach to all tropical wetland broad-leaf trees yields an estimated non-flooded floodplain tree flux of 6.4 Tg CH4 yr−1 which, at 17% of the flooded tropical tree flux of approximately 37.1 Tg CH4 yr−1, demonstrates the importance of these ecosystems in extending the effective CH4 emitting area beyond flooded lands.This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Methanogenesis and Salt Tolerance Genes of a Novel Halophilic Methanosarcinaceae Metagenome-Assembled Genome from a Former Solar Saltern.

Anaerobic archaeal methanogens are key players in the global carbon cycle due to their role in the final stages of organic matter decomposition in anaerobic environments such as wetland sediments. Here we present the first draft metagenome-assembled genome (MAG) sequence of an unclassified Methanosarcinaceae methanogen phylogenetically placed adjacent to the Methanolobus and Methanomethylovorans genera that appears to be a distinct genus and species. The genome is derived from sediments of a hypersaline (97–148 ppt chloride) unrestored industrial saltern that has been observed to be a significant methane source. The source sediment is more saline than previous sources of Methanolobus and Methanomethylovorans. We propose a new genus name, Methanosalis, to house this genome, which we designate with the strain name SBSPR1A. The MAG was binned with CONCOCT and then improved via scaffold extension and reassembly. The genome contains pathways for methylotrophic methanogenesis from trimethylamine and dimethylamine, as well as genes for the synthesis and transport of compatible solutes. Some genes involved in acetoclastic and hydrogenotrophic methanogenesis are present, but those pathways appear incomplete in the genome. The MAG was more abundant in two former industrial salterns than in a nearby reference wetland and a restored wetland, both of which have much lower salinity levels, as well as significantly lower methane emissions than the salterns.

Estimation of methane emissions from municipal solid waste landfill in makassar city based on ipcc waste model

One of the greenhouse gases, which is the cause of climate change and global warming is methane gas (CH4). One of the most significant sources of methane that contributes to emissions globally is landfills (anthropogenic sources). Methane emissions from waste are the result of the anaerobic decomposition of organic matter in waste. The more garbage in the landfill without further treatment can lead to greater methane emissions. The site of this study was a municipal solid waste in Makassar city, named Tamangapa landfill, ±15 km from downtown Makassar city. The objectives of this study are to estimate methane emissions in the Tamangapa landfill and estimate methane emissions from the Tamangapa landfill over the next ten years using the 2006 IPCC Waste Model. The results showed that the waste generation in Makassar City, in 2016, was 0.449 kg/person/day with the composition of waste dominated by organic waste. The value of potential methane emissions at TPA Tamangapa Makassar in 2016 is 2.24 Gg/year and the projection in 2026 is 4.968 Gg/year. The mitigation and adaptation efforts that can be recommended are the socialization of 3R techniques (Reduce, Reuse, and Recycle) and construct a sanitary landfill in Makassar city following the mandate of Law No. 18 of 2008.

Methods for instrumental assessment of methane emission in reservoirs

Reservoirs are a significant source of methane in the atmosphere. Different estimations of the total methane emission from reservoirs vary greatly. In order to more accurately estimation of the methane emission from reservoirs, it is necessary to investigate the spatiotemporal variability of CH4 fluxes. To study this variability, detailed instrumental measurements of methane fluxes over a long period are required. Such measurements have been carried out for 6 years at the Mozhaisk Reservoir. These measurements showed that the determining factor of the spatiotemporal methane fluxes variability is the meteorological situation and the water level regime. These factors form the stratification of the water column. The highest values of methane flux into the atmosphere are observed in the middle part of the reservoir. The temporal variation of the methane flux is characterized by a general pattern for all years when the measurements were carried out. The methane flux increases during the summer period and reaches the highest values before the beginning of the autumn mixing stage. Also, high flux values observed during periods of storm events that cause mixing of the water column.

The anaerobic oxidation of methane in paddy soil by ferric iron and nitrate, and the microbial communities involved

The anaerobic oxidation of methane (AOM) mediated by microorganisms is a key process in the reduction of methane emissions, and AOM-coupled electron acceptors have been shown to regulate methane emissions into the atmosphere in marine systems. Paddy fields are a significant source of methane and account for 20% of global methane emissions, but the effect of electron acceptors on the methane emission process in flooded paddy fields has been poorly characterized. This study aimed to determine whether the electron acceptors ferric iron and nitrate, and biochar, acting as an electron shuttle, can regulate the AOM process in paddy soil, with or without interaction between biochar and these two electron acceptors. We also aimed to characterize which microorganisms are actively involved. Here, we added 13C-labeled CH4 (13CH4) into anaerobic microcosms to evaluate the role of electron acceptors by measuring the methane oxidation rate and the enrichment of 13C-labeled CO2 (13CO2). We then combined DNA-stable isotope probing with amplicon sequencing to study the active microorganisms. We found for the first time that, in addition to nitrate, ferric iron can also effectively promote AOM in paddy soil. However, there was no significant effect of biochar. Ferric iron-dependent AOM was mainly carried out by iron-reducing bacteria (Geobacter, Ammoniphilus and Clostridium), and nitrate-dependent AOM was mainly by nitrate-reducing bacteria (Rhodanobacter, Paenibacillus and Planococcus). Our results demonstrate that the AOM process, regulated by the electron acceptors ferric iron and nitrate, can alleviate methane emission from paddy soil. The potentially active microorganisms related to electron acceptor reduction may be crucial for this methane sink and deserve further research.

Peripheral freshwater deltaic wetlands are hotspots of methane flux in the coastal zone

Methane (CH4) emissions are low in the coastal zone due to a higher redox poise, related to sulfate reduction. However, river deltas are a potential source of CH4 flux in coastal zones globally, due to fresh condition and high primary production. The goal of this study was to seasonally measure CH4flux at three different geomorphic settings (newly forming island, river channel bottom and established freshwater marsh) within the Wax Lake Delta, Louisiana, USA. CH4 flux rates were 386 ± 327 mg C m−2 d−1 in March and 2859 ± 1286 mg C m−2 d−1 in June at the freshwater marsh site. At the island site, CH4 flux was significantly smaller at 7.94 ± 3.57 mg C m−2 d−1 in March and 215 ± 153 mg C m−2 d−1 in June while at adjacent river channel bottom site, CH4 flux was lowest at 2.49 ± 3.38 mg C m−2 d−1 in March and 19.5 ± 1.12 mg C m−2 d−1 in June at the air-water interface. CH4 emission rates show significant spatial heterogeneity with rates up to two orders of magnitude greater at the marsh site at the periphery of the delta, related to greater soil total C. Therefore regions within the active delta do not provide a significant source of methane, due to a lack of soil C, despite freshwater conditions. However, marshes at the periphery within the halo of fresh water, populated with established plant communities can be significant hotspots of CH4 emissions, despite their location within the coastal zone.

Using Water Table Depths Inferred From Testate Amoebae to Estimate Holocene Methane Emissions From the Hudson Bay Lowlands, Canada

AbstractWetlands are the largest natural source of methane, yet the roles of source region and paleoclimate in explaining the variability in Holocene atmospheric methane concentrations remain poorly constrained. The Hudson Bay Lowlands (HBL) is one of the world's largest continuous peatland regions and a significant source of methane. We present here, using a novel proxy‐based approach, Holocene methane fluxes for the HBL. Paleo‐methane fluxes were quantified based on water table depth (WTD), inferred from testate amoeba assemblages in nine peat records. WTDs were reconstructed using a North American transfer function and were used to estimate paleo‐methane flux through a linear regression model of contemporary growing season methane fluxes and WTDs from 88 sites across the region. Following HBL peatland initiation in the Middle Holocene, total methane flux is closely related to the increasing area of land emerging from below sea level, controlled by rapid rates of glacial isostatic adjustment. In the Late Holocene, rates of uplift slowed, but methane fluxes remained high due to lower evapotranspiration in a wetter and cooler climate. We estimate that 4.8 ± 1.6 Pg C has been released from HBL peatlands to the atmosphere as CH4 over the last 8,000 years, with an average annual methane emission of 1.1 Tg CH4 yr−1 in the Late Holocene. The values estimated here are broadly consistent with those calculated from other independent methods, on modern and Holocene timescales, demonstrating that testate amoeba records provide an effective approach for scaling local processes to regional paleo‐methane emissions.