Net Methane Emissions Research Articles

Solid phase speciation controls copper mobilisation from marine sediments by methanobactin

Although marine environments represent huge reservoirs of the potent greenhouse gas methane, they currently contribute little to global net methane emissions. Most of the methane is oxidized by methanotrophs, minimizing escape to the atmosphere. Aerobic methanotrophs oxidize methane mostly via the copper (Cu)-bearing enzyme particulate methane monooxygenase (pMMO). Therefore, aerobic methane oxidation depends on sufficient Cu acquisition by methanotrophs. Because they require both oxygen and methane, aerobic methanotrophs reside at oxic-anoxic interfaces, often close to sulphidic zones where Cu bioavailability can be limited by poorly soluble Cu sulphide mineral phases. Under Cu-limiting conditions, certain aerobic methanotrophs exude Cu-binding ligands termed chalkophores, such as methanobactin (mb) exuded by Methylosinus trichosporium OB3b. Our main objective was to establish whether chalkophores can mobilise Cu from Cu sulphide-bearing marine sediments to enhance Cu bioavailability.Through a series of kinetic batch experiments, we investigated Cu mobilisation by mb from a set of well-characterized sulphidic marine sediments differing in sediment properties, including Cu content and phase distribution. Characterization of solid-phase Cu speciation included X-ray absorption spectroscopy and a targeted sequential extraction. Furthermore, in batch experiments, we investigated to what extent adsorption of metal-free mb and Cu-mb complexes to marine sediments constrains Cu mobilisation.Our results are the first to show that both solid phase Cu speciation and chalkophore adsorption can constrain methanotrophic Cu acquisition from marine sediments. Only for certain sediments did mb addition enhance dissolved Cu concentrations. Cu mobilisation by mb was not correlated to the total Cu content of the sediment, but was controlled by solid-phase Cu speciation. Cu was only mobilised from sediments containing a mono-Cu-sulphide (CuSx) phase. We also show that mb adsorption to sediments limits Cu acquisition by mb to less compact (surface) sediments. Therefore, in sulphidic sediments, mb-mediated Cu acquisition is presumably constrained to surface-sediment interfaces containing mono-Cu-sulphide phases.

Addressing Methane Venting: Strategies and Implications on the Environment

Industrial processes, including oil and gas production, landfill operations, and agriculture, emit methane, a potent greenhouse gas. This article examined methane emissions in Rivers State's Soku, Agbada, and Oyigbo oil and gas extraction communities. The net methane emissions(mg/l) for facilities A, B, and C are 0.90, 0.28, and 1.03, respectively. The corresponding temperature rise for the host communities over the same period were 1.87 oC, 0.37 oC, and 1.16 oC, respectively. All three sites have near-neutral unstable methane dispersion using Monin-Obukhov length. This article examined new methane venting mitigation technologies and their effects on bioenergy and environmental engineering. The study analyzed existing methane venting trends in several Rivers State oil production sites and their effects on local temperature and the environment, emphasizing the necessity for adequate mitigation. This paper also examined new methane capture, use, and sequestration technologies. The article also examines methane mitigation and bioenergy industry synergies, stressing co-benefit strategies that improve sustainability and economic feasibility. Methane mitigation strategies in Rivers State increase energy efficiency, carbon footprint, and air quality, according to the paper. This study helps reduce methane emissions by providing possible alternatives and their effects on bioenergy development and environmental stewardship. Interdisciplinarity and innovation are encouraged to accelerate sustainable and resilient development.

Effects of Antibiotics on the DAMO Process and Microbes in Cattle Manure.

Denitrifying anaerobic methane oxidation (DAMO) can mitigate methane emissions; however, this process has not been studied in cattle manure, an important source of methane emissions in animal agriculture. The objective of this study was to investigate the occurrence of DAMO microbes in cattle manure and examine the impacts of veterinary antibiotics on the DAMO process in cattle manure. Results show that DAMO archaea and bacteria consistently occur at high concentrations in beef cattle manure. During the long-term operation of a sequencing batch reactor seeded with beef cattle manure, the DAMO activities intensified, and DAMO microbial biomass increased. Exposure to chlortetracycline at initial concentrations up to 5000 μg L-1 did not inhibit DAMO activities or affect the concentrations of the 16S rRNA gene and functional genes of DAMO microbes. In contrast, exposure to tylosin at initial concentrations of 50 and 500 μg L-1 increased the activities of the DAMO microbes. An initial concentration of 5000 μg L-1 TYL almost entirely halted DAMO activities and reduced the concentrations of DAMO microbes. These results show the occurrence of DAMO microbes in cattle manure and reveal that elevated concentrations of dissolved antibiotics could inhibit the DAMO process, potentially affecting net methane emissions from cattle manure.

Warming and wetting-induced soil acidification triggers methanotrophic diversity loss and species turnover in an alpine ecosystem

Increases in temperature and precipitation have continually occurred in the past few decades, both globally and in China, which have probably impacted the dynamics of net methane (CH4) emissions by regulating soil CH4 oxidization. An alpine ecosystem is quite sensitive to climate changes, but how these two climatic factors regulate the community of soil aerobic methane-oxidizing bacteria (aMOB) remains elusive in such an ecosystem because of the lack of high-resolution soil sampling datasets. Here, we employed a hybrid approach of gridded field surveys and random forest prediction to discern the above question in the Qinghai-Tibetan Plateau (QTP). Results indicated that type Ic aMOBs exhibited a preference for drier, colder areas, while type IIa, TUSC-like and RA21-like aMOBs probably occurred in wetter and relatively warmer areas. There were no remarkable shifts in α-diversity and bacterial community compositions from the driest and coldest regions to moderate ones, while the α-diversity decreased and community compositions changed substantially from moderate arid and cold areas to wetter, relatively warmer ones. These trends were mainly regulated by soil pH, a potentially secondary effect shaped by the interactions of mean annual precipitation (MAP) and temperature (MAT) and an aridity index (AI) in the QTP. A slight decline in soil pH from the driest and coldest areas to moderate ones might regulate aMOB diversity and community structure by the stochastic extinction of individuals adapted to a higher pH and the unstable colonization of individuals preferring a moderate pH. A great decline in soil pH from the moderate arid, cold to wetter, relatively warmer areas might lead to the deterministic exclusion of species with a high pH adaptability and the stable colonization of species preferring the acidic habitat. This study implies that soil acidification probably induces aMOB diversity loss and species turnover in the arid, cold areas of the QTP under climatic warming and wetting, shedding a new light on projecting the impact of climate changes on an alpine ecosystem’s structure and function on unprecedented spatial scales.

Methane Emissions From Land and Aquatic Ecosystems in Western Siberia: An Analysis With Methane Biogeochemistry Models

AbstractWestern Siberia contains extensive wetlands and aquatic ecosystems, contributing a significant amount of methane (CH4) emissions to the atmosphere. However, estimates of CH4 fluxes over the region are poorly constrained partly due to the uncertainties from the inundated area data. This study applied two process‐based biogeochemistry models to quantify the emissions from land and aquatic ecosystems over the region within the period 2000–2021 using different inundation datasets. To drive land methane modeling, we use one static wetland map and one dynamic wetland area data set called Wetland Area and Dynamics for Methane Modeling (WAD2M) (2000–2020). To drive lake methane modeling, we use the surface area of aquatic ecosystems from three datasets: (a) HydroLAKES; (b) Global Surface Water (GSW); and (c) surface water inundation from Soil Moisture Active Passive (SMAP) (2016–2021). Using these datasets, we conduct four simulations to compare emissions over the region. We find that the net methane emissions from land using the static wetland map are larger than those using WAD2M. SMAP and GSW estimate larger emissions than HydroLAKES does from aquatic ecosystems. Total emissions over the region range from 4.80 ± 0.43 to 8.29 ± 0.81 Tg CH4/year from 2016 to 2020, which is the intersection period of four simulations. This study is among the first to investigate methane emissions from the whole landscape in the region. Our study highlights the importance of dynamic wetland and aquatic area data in quantifying regional methane emissions.

Capturing the rapid response of sediments to low-oxygen conditions with high temporal resolution gas concentration measurements

Low-oxygen conditions plague coastlines worldwide. At present, little is known about how the transition from normoxic to low or even no oxygen conditions alters sediment biogeochemical cycling and ultimately ecosystem functioning. Conventional sediment core incubations cannot capture rapid (<hourly) changes in biogenic gas fluxes that may occur due to oxygen depletion. To better constrain the response of sediments to hypoxia, we employed a novel flow-injection system coupled to a membrane inlet mass spectrometer to quantify fluxes oxygen, dinitrogen, and methane across the sediment-water interface from a temperate estuary (Narragansett Bay, Rhode Island, United States). We evaluated how sediments from a site more impacted by nitrogen pollution compare to one less impacted by nitrogen in response to organic matter addition. Our system is able to sample every 10 minutes, allowing us to cycle through triplicate core measurements roughly every 30 minutes to track the response of sediments to increasing hypoxic severity. The high temporal-resolution data revealed dynamic changes in sediment-water gas fluxes, suggesting that reactive nitrogen removal is enhanced under mild hypoxia but dampened under prolonged hypoxia to anoxia. Further we found that organic matter loading enhances both net denitrification and methane emissions. Ultimately, our approach represents a powerful new tool for advancing our knowledge of short-term temporal dynamics in benthic biogeochemical cycling.

Twinning in cattle: a pathway for reducing the methane intensity of beef

Context Reducing livestock emissions, the largest single contributor to agricultural emissions, is increasingly recognised as a high priority. The low biological efficiency of beef cattle, due to their long gestation period, long generational interval, and propensity to be uniparous, contributes to the high methane emissions intensity (kg CO2-e/kg product) of beef compared to most other food products. Aims We evaluate the potential of increasing the frequency of multiparous births (twinning) as a pathway to reducing the methane intensity of beef and the net methane emissions of intensive beef systems. Methods We simulate a uniparous herd structure and emissions profile using GrassGro™ livestock systems modelling software and then calculate the effects of an increasing frequency of multiparous births (twinning), up to 1.53 calves per cow joined, on methane emissions. Key results Our results demonstrate that beef from calves reared as twins has a 22% lower methane intensity than beef from a single reared calf. Although twinning reduces the methane intensity of beef, at the herd level, net methane emissions could rise by as much as 23% at 1.53 calves per cow joined if overall herd size is allowed to grow through an increased number of calves. If we decrease stocking rates, whilst also increasing twinning rates, it is possible to reduce net emissions by up to 14%, without changing productivity. Conclusions Our results illustrate the significant potential of twinning to decrease the methane intensity of beef and to increase the productivity per cow in intensive beef systems. Implications Despite this, twinning is unlikely to be a viable net emissions reduction pathway – as twinning will increase stocking rate unless herd structure is altered – unless a commercial or policy driver to reduce net methane emissions is established.

RNA Biomarker Trends across Type I and Type II Aerobic Methanotrophs in Response to Methane Oxidation Rates and Transcriptome Response to Short-Term Methane and Oxygen Limitation in Methylomicrobium album BG8.

ABSTRACTMethanotrophs, which help regulate atmospheric levels of methane, are active in diverse natural and man-made environments. This range of habitats and the feast-famine cycles seen by many environmental methanotrophs suggest that methanotrophs dynamically mediate rates of methane oxidation. Global methane budgets require ways to account for this variability in time and space. Functional gene biomarker transcripts are increasingly studied to inform the dynamics of diverse biogeochemical cycles. Previously, per-cell transcript levels of the methane oxidation biomarker pmoA were found to vary quantitatively with respect to methane oxidation rates in the model aerobic methanotroph Methylosinus trichosporium OB3b. In the present study, these trends were explored for two additional aerobic methanotroph pure cultures grown in membrane bioreactors, Methylocystis parvus OBBP and Methylomicrobium album BG8. At steady-state conditions, per-cell pmoA mRNA transcript levels strongly correlated with per-cell methane oxidation across the three methanotrophs across many orders of magnitude of activity (R2 = 0.91). The inclusion of both type I and type II aerobic methanotrophs suggests a universal trend between in situ activity level and pmoA RNA biomarker levels which can aid in improving estimates of both subsurface and atmospheric methane. Additionally, genome-wide expression data (obtained by transcriptome sequencing [RNA-seq]) were used to explore transcriptomic responses of steady-state M. album BG8 cultures to short-term CH4 and O2 limitation. These limitations induced regulation of genes involved in central carbon metabolism (including carbon storage), cell motility, and stress response.IMPORTANCE Methanotrophs are naturally occurring microorganisms capable of oxidizing methane, having an impact on global net methane emissions. Additionally, they have also gained interest for their biotechnological applications in single-cell protein production, biofuels, and bioplastics. Having better ways of measuring methanotroph activity and understanding how methanotrophs respond to changing conditions is imperative for both optimization in controlled-growth applications and understanding in situ methane oxidation rates. In this study, we explored the applicability of methane oxidation biomarkers as a universal indicator of methanotrophic activity and explored methanotroph transcriptomic response to short-term changes in substrate availability. Our results contribute to better understanding the activity of aerobic methanotrophs, their core metabolic pathways, and their stress responses.

Brown carbon from biomass burning imposes strong circum-Arctic warming

Brown carbon from biomass burning imposes strong circum-Arctic warming

Effective Mainstreaming of Agricultural Emissions into Climate Action Agenda: The Case of Institutions and Smallholder Dairy Production Systems, Western Kenya

Small-scale farming production systems are integral drivers of global sustainability challenges and the climate crisis as well as a solution space for the transition to climate compatible development. However, mainstreaming agricultural emissions into a climate action agenda through integrative approaches, such as Climate Smart Agriculture (CSA), largely reinforces adaptation–mitigation dualism and pays inadequate attention to institutions’ linkage on the generation of externalities, such as Greenhouse Gas (GHG) emissions. This may undermine the effectiveness of local–global climate risk management initiatives. Literature data and a survey of small-scale farmers’ dairy feeding strategies were used in the simulation of GHG emissions. The effect of price risks on ecoefficiencies or the amount of GHG emissions per unit of produced milk is framed as a proxy for institutional feedbacks on GHG emissions and effect at scale. This case study on small-scale dairy farmers in western Kenya illustrates the effect of local-level and sectoral-level institutional constraints, such as market risks on decision making, on GHG emissions and the effectiveness of climate action. The findings suggest that price risks are significant in incentivising the adoption of CSA technologies. Since institutional interactions influence the choice of individual farmer management actions in adaptation planning, they significantly contribute to GHG spillover at scale. This can be visualised in terms of the nexus between low or non-existent dairy feeding strategies, low herd productivity, and net higher methane emissions per unit of produced milk in a dairy value chain. The use of the Sustainable Food Value Chain (SFVC) analytical lens could mediate the identification of binding constraints, foster organisational and policy coherence, as well as broker the effective mainstreaming of agricultural emissions into local–global climate change risk management initiatives. Market risks thus provide a systematic and holistic lens for assessing alternative carbon transitions, climate financing, adaptation–mitigation dualism, and the related risk of maladaptation, all of which are integral in the planning and implementation of effective climate action initiatives.

Influences of phosphorus and potassium deficiencies on the methanotrophic communities in rice rhizosphere

Soil methanotrophs can modulate net methane (CH4) emissions in rice paddy fields, but their growth and development depend, to a great extent, upon the soil nutrient status. In this study, a pot experiment was conducted to explore how deficiencies in soil phosphorus (P) or potassium (K) affect the methanotrophic abundance (based on pmoA q-PCR), community composition (based on MiSeq high-throughput sequencing) and CH4 oxidation potential using historically severe P and K deficient paddy soils, respectively. The results showed that P deficiency induced a significant decrease in methanotrophic abundance and potential activity in both rhizosphere and bulk soils. Additionally, P deficiency also caused clear shifts in the methanotrophic community composition within the rhizosphere, where the relative abundance of type II methanotrophs (e.g., Methylocystis and Methylosinus) increased while type I (e.g., Methylomonas, Methylobacter and Unclassified_typeIb) decreased. In contrast, K deficiency did not significantly affect the methanotrophic potential activity and community composition in both rhizosphere and bulk soils. More interestingly, P or K deficiency, particularly P deficiency, narrowed the differences in the abundance and community composition between rhizosphere and bulk soils, implying that P and K deficiencies could attenuate the rhizosphere effects on methanotrophic communities by limiting rice plant growth. Collectively, our results indicated that soil P deficiency, would inhibit soil CH4 oxidation directly or indirectly through restricting rice plant growth, while K deficiency have slight effects on the activity and community composition of soil methanotrophs.

Policy to Reduce Greenhouse Gas Emissions: Is Agricultural Methane a Special Case?

SummaryClimate change mitigation will require significant efforts from all emitting sectors, including agriculture. However, agricultural emission reduction measures raise specific concerns, both in respect of their distinct climate outcomes and how their implementation might support or frustrate wider objectives. We highlight some special characteristics regarding agricultural methane emissions. As methane is a relatively short‐lived gas, we do not have the same strong physical requirement to completely eliminate net methane emissions as we do for carbon dioxide. An appreciation of the distinct nature and impacts of carbon dioxide and methane can bring nuance to discussions; especially around what different sectors must be expected to achieve, and thus help avoid negative trade‐offs that might result from heavy‐handed policy interventions. Nevertheless, significant and rapid methane emission reductions do remain important in realistically achieving our overall climate objectives. A number of technical measures to reduce ruminant methane are highlighted, but are not without their own challenges; and we are unlikely to meet climate or other environmental targets without systemic changes to the total food system, including overall consumption patterns. The appropriate policy tools to achieve these changes are emerging as a key, but contested, concern in Europe and beyond, making it vital we work through these arguments in a transparent manner.

Methane utilizing plant growth-promoting microbial diversity analysis of flooded paddy ecosystem of India.

Methane utilizing bacteria (MUB) are known to inhabit the flooded paddy ecosystem where they play an important role in regulating net methane (CH4) emission. We hypothesize that efficient MUB having plant growth-promoting (PGP) attributes can be used for developing novel bio-inoculant for flooded paddy ecosystem which might not only reduce methane emission but also assist in improving the plant growth parameters. Hence, soil and plant samples were collected from the phyllosphere, rhizosphere, and non-rhizosphere of five rice-growing regions of India at the tillering stage and investigated for efficient methane-oxidizing and PGP bacteria. Based on the monooxygenase activity and percent methane utilization on NMS medium with methane as the sole C source, 123 isolates were identified and grouped phylogenetically into 13 bacteria and 2 yeast genera. Among different regions, a significantly higher number of isolates were obtained from lowland flooded paddy ecosystems of Aduthurai (33.33%) followed by Ernakulum (20.33%) and Brahmaputra valley (19.51%) as compared to upland irrigated regions of Gaya (17.07%) and Varanasi (8.94%). Among sub-samples, a significantly higher number of isolates were found inhabiting the phyllosphere (58.54%) followed by non-rhizosphere (25.20%) and rhizosphere (15.45%). Significantly higher utilization of methane and PGP attributes were observed in 30 isolates belonging to genera Hyphomicrobium, Burkholderia, Methylobacterium, Paenibacillus,Pseudomonas,Rahnella, andMeyerozyma.M. oryzaeMNL7 showed significantly better growth with 74.33% of CH4 utilization at the rate of 302.9 ± 5.58 and exhibited half-maximal growth rate, Ksof 1.92 ± 0.092mg CH4L-1. Besides the ability to utilize CH4,P. polymyxaMaAL70 possessed PGP attributes such as solubilization of P, K, and Zn, fixation of atmospheric N and production of indole acetic acid (IAA). Both these promising isolates can be explored in the future for developing novel biofertilizers for flooded paddies.

Inoculation of plant growth promoting-methane utilizing bacteria in different N-fertilizer regime influences methane emission and crop growth of flooded paddy

Methane (CH4) emission in rice fields is greatly influenced by the type and quantity of nitrogenous fertilizer used. The net methane emission from paddy fields is also influenced by the activity of methane utilizing bacteria, which inhabit the flooded paddy ecosystem. Efficient methane utilizing and plant growth promoting bacteria Methylobacterium oryzae MNL7 and Paenibacillus polymyxa MaAL70, respectively were co-inoculated along with different nitrogenous fertilizer combinations in flooded paddy to assess their impact on cumulative methane emission and crop growth promotion. Co-inoculation significantly influenced the plant growth parameters of paddy, resulting in an increase in grain yield by 14.04, 11.08, and 12.38% in treatments receiving Urea, Di-ammonium Phosphate (DAP) + Urea, or farm yard manure (FYM), over their respective un-inoculated plots. Significant improvement in the rice grain nutrient quality in term of crude protein, Fe and Zn content was observed as a result of bacterial co-inoculation in FYM fertilized plots as compared to Urea and DAP+ Urea fertilized plots. Significantly higher cumulative methane emission of 63.39 kg ha−1 was observed in uninoculated plots fertilized with FYM treatment as compared to Urea (33.83 kg ha−1) and DAP+Urea (31.66 kg ha−1) treatments. Bacterial co-inoculation significantly reduced the cumulative methane emission by 12.03, 11.47 and 6.92% in Urea, DAP+Urea, and FYM fertilized plots over their respective uninoculated treatments. Among the different fertilizer treatments, bacterial co-inoculation with urea application performed significantly better in reducing cumulative methane emission. These findings suggest that methane utilizing bacteria which also possess plant growth promoting trait can be explored for developing a novel biofertilizer for flooded paddies, as they can aid in managing both the overall methane emission and enhancing crop yield.

Multiple processes contribute to methane emission in a riparian cottonwood forest ecosystem.

Methane emission from trees may partially or completely offset the methane sink in upland soils, the only process that has been regularly included in methane budgets for forest ecosystems. Our objective was to analyze multiple biogeochemical processes that influence the production, oxidation and transport of methane in a riparian cottonwood ecosystem and its adjacent river. We combined chamber flux measurements on tree stems, forest soil and the river surface with eddy covariance measurements of methane net ecosystem exchange. In addition, we tested whether methanogens were present in cottonwood stems, shallow soil layers and alluvial groundwater. Average midday peak in net methane emission measured by eddy covariance was c. 12nmolm-2 s-1 . The average uptake of methane by soils (0.87nmolm-2 s-1 ) was largely offset by tree stem methane emission (0.75nmolm-2 s-1 ). There was evidence of methanogens in tree stems but not in shallow soil. Growing season (May-September) cumulative net methane emission (17.4mmolCH4 m-2 ) included methane produced in cottonwood stems and methane input to the nocturnal boundary layer from the forest and the adjacent river. The multiple processes contributing to methane emission illustrated the linked nature of these adjacent terrestrial and aquatic ecosystems.

Infectious Diseases, Livestock, and Climate: A Vicious Cycle?

Ruminant livestock are a significant contributor to global methane emissions. Infectious diseases have the potential to exacerbate these contributions by elevating methane outputs associated with animal production. With the increasing spread of many infectious diseases, the emergence of a vicious climate–livestock–disease cycle is a looming threat.

Methane Monooxygenase Gene Transcripts as Quantitative Biomarkers of Methanotrophic Activity in Methylosinus trichosporium OB3b.

Methanotrophic microorganisms are characterized by their ability to oxidize methane. Globally they have a significant impact on methane emissions by attenuating net methane fluxes to the atmosphere in natural and engineered systems, though the populations are dynamic in their activity level in soils and waters. Methanotrophs oxidize methane using methane monooxygenase (MMO) enzymes, and selected subunit genes of the most common MMOs, specifically pmoA and mmoX, are used as biomarkers for the presence and abundance of populations of bacterial methanotrophs. The relative expression of these biomarker genes is dependent on copper-to-biomass ratios. Empirically derived quantitative relationships between methane oxidation biomarker transcript amounts and methanotrophic activity could facilitate determination of methane oxidation rates. In this study, pure cultures of a model type II methanotroph, Methylosinus trichosporium OB3b, were grown in hollow-fiber membrane bioreactors (HFMBR) under different steady-state methane oxidation conditions. Methanotroph biomass (DNA based) and methane oxidation biomarker mRNA transcript amounts were determined using quantitative PCR (qPCR) and reverse transcription-PCR (RT-qPCR), respectively. Under both copper-present and copper-limited conditions, per-cell pmoA mRNA transcript levels positively correlated with measured per-cell methane oxidation rates across 3 orders of magnitude. These correlations, if maintained across different methanotrophs, could prove valuable for inferring in situ oxidation rates of methanotrophs and understanding the dynamics of their impact on net methane emissions.IMPORTANCE Methanotrophs are naturally occurring microorganisms capable of oxidizing methane and have an impact on global net methane emissions. The genes pmoA and mmoX are used as biomarkers for bacterial methanotrophs. Quantitative relationships between transcript amounts of these genes and methane oxidation rates could facilitate estimation of methanotrophic activity. In this study, a strong correlation was observed between per-cell pmoA transcript levels and per-cell methane oxidation rates for pure cultures of the aerobic methanotroph M. trichosporium OB3b grown in bioreactors. If similar relationships exist across different methanotrophs, they could prove valuable for inferring in situ oxidation rates of methanotrophs and better understanding their impact on net methane emissions.

Uncertainty Quantification of Global Net Methane Emissions From Terrestrial Ecosystems Using a Mechanistically Based Biogeochemistry Model

AbstractQuantification of methane (CH4) emissions from wetlands and its sinks from uplands is still fraught with large uncertainties. Here, a methane biogeochemistry model was revised, parameterized, and verified for various wetland ecosystems across the globe. The model was then extrapolated to the global scale to quantify the uncertainty induced from four different types of uncertainty sources including parameterization, wetland type distribution, wetland area distribution, and meteorological input. We found that global wetland emissions are 212 ± 62 and 212 ± 32 Tg CH4 year−1 (1Tg = 1012 g) due to uncertain parameters and wetland type distribution, respectively, during 2000–2012. Using two wetland distribution data sets and three sets of climate data, the model simulations indicated that the global wetland emissions range from 186 to 212 CH4 year−1 for the same period. The parameters were the most significant uncertainty source. After combining the global methane consumption in the range of −34 to −46 Tg CH4 year−1, we estimated that the global net land methane emissions are 149–176 Tg CH4 year−1 due to uncertain wetland distribution and meteorological input. Spatially, the northeast United States and Amazon were two hotspots of methane emission, while consumption hotspots were in the Eastern United States and eastern China. During 1950–2016, both wetland emissions and upland consumption increased during El Niño events and decreased during La Niña events. This study highlights the need for more in situ methane flux data, more accurate wetland type, and area distribution information to better constrain the model uncertainty.

Methane emissions from underground gas storage in California

Accurate and timely detection, quantification, and attribution of methane emissions from Underground Gas Storage (UGS) facilities is essential for improving confidence in greenhouse gas inventories, enabling emission mitigation by facility operators, and supporting efforts to assess facility integrity and safety. We conducted multiple airborne surveys of the 12 active UGS facilities in California between January 2016 and November 2017 using advanced remote sensing and in situ observations of near-surface atmospheric methane (CH4). These measurements where combined with wind data to derive spatially and temporally resolved methane emission estimates for California UGS facilities and key components with spatial resolutions as small as 1–3 m and revisit intervals ranging from minutes to months. The study spanned normal operations, malfunctions, and maintenance activity from multiple facilities including the active phase of the Aliso Canyon blowout incident in 2016 and subsequent return to injection operations in summer 2017. We estimate that the net annual methane emissions from the UGS sector in California averaged between 11.0 ± 3.8 GgCH4 yr−1 (remote sensing) and 12.3 ± 3.8 GgCH4 yr−1 (in situ). Net annual methane emissions for the 7 facilities that reported emissions in 2016 were estimated between 9.0 ± 3.2 GgCH4 yr−1 (remote sensing) and 9.5 ± 3.2 GgCH4 yr−1 (in situ), in both cases around 5 times higher than reported. The majority of methane emissions from UGS facilities in this study are likely dominated by anomalous activity: higher than expected compressor loss and leaking bypass isolation valves. Significant variability was observed at different time-scales: daily compressor duty-cycles and infrequent but large emissions from compressor station blow-downs. This observed variability made comparison of remote sensing and in situ observations challenging given measurements were derived largely at different times, however, improved agreement occurred when comparing simultaneous measurements. Temporal variability in emissions remains one of the most challenging aspects of UGS emissions quantification, underscoring the need for more systematic and persistent methane monitoring.

Reduced net methane emissions due to microbial methane oxidation in a warmer Arctic

Methane emissions from organic-rich soils in the Arctic have been extensively studied due to their potential to increase the atmospheric methane burden as permafrost thaws1–3. However, this methane source might have been overestimated without considering high-affinity methanotrophs (HAMs; methane-oxidizing bacteria) recently identified in Arctic mineral soils4–7. Herein we find that integrating the dynamics of HAMs and methanogens into a biogeochemistry model8–10 that includes permafrost soil organic carbon dynamics3 leads to the upland methane sink doubling (~5.5 Tg CH4 yr−1) north of 50 °N in simulations from 2000–2016. The increase is equivalent to at least half of the difference in net methane emissions estimated between process-based models and observation-based inversions11,12, and the revised estimates better match site-level and regional observations5,7,13–15. The new model projects doubled wetland methane emissions between 2017–2100 due to more accessible permafrost carbon16–18. However, most of the increase in wetland emissions is offset by a concordant increase in the upland sink, leading to only an 18% increase in net methane emission (from 29 to 35 Tg CH4 yr−1). The projected net methane emissions may decrease further due to different physiological responses between HAMs and methanogens in response to increasing temperature19,20. Models overestimate Arctic methane emissions compared to observations. Incorporating microbial dynamics into biogeochemistry models helps reconcile this discrepancy; high-affinity methanotrophs are an important part of the Arctic methane budget and double previous estimates of methane sinks.