Fate Of Methane Research Articles

Fate of methane in canals draining tropical peatlands

AbstractTropical wetlands and freshwaters are major contributors to the growing atmospheric methane (CH4) burden. Extensive peatland drainage has lowered CH4 emissions from peat soils in Southeast Asia, but the canals draining these peatlands may be hotspots of CH4 emissions. Alternatively, CH4 oxidation (consumption) by methanotrophic microorganisms may attenuate emissions. Here, we used laboratory experiments and a synoptic survey of the isotopic composition of CH4 in 34 canals across West Kalimantan, Indonesia to quantify the proportion of CH4 that is consumed and therefore not emitted to the atmosphere. We find that CH4 oxidation mitigates 76.4 ± 12.0% of potential canal emissions, reducing emissions by ~70 mg CH4 m−2 d−1. Methane consumption also significantly impacts the stable isotopic fingerprint of canal CH4 emissions. As canals drain over 65% of peatlands in Southeast Asia, our results suggest that CH4 oxidation significantly influences landscape-scale CH4 emissions from these ecosystems.

Biomass Storage in Anoxic Marine Basins: Initial Estimates of Geochemical Impacts and CO2 Sequestration Capacity

AbstractIn combination with dramatic and immediate CO2 emissions reductions, net‐negative atmospheric CO2 removal (CDR) is necessary to maintain average global temperature increases below 2.0°C. Many proposed CDR pathways involve the placement of vast quantities of organic carbon (biomass) on the seafloor in some form, but little is known about their potential biogeochemical impacts, especially at scales relevant for global climate. Here, we evaluate the potential impacts and durability of organic carbon storage specifically within deep anoxic basins, where organic matter (OM) is remineralized through anaerobic processes that may enhance its storage efficiency. We present simple biogeochemical and mixing models to quantify the scale of potential impacts of large‐scale OM addition to the abyssal seafloor in the Black Sea, Cariaco Basin, and the hypersaline Orca Basin. These calculations reveal that the Black Sea in particular may have the potential to accept biomass storage at climatically relevant scales with moderate changes to the geochemical state of abyssal water and limited communication of that impact to surface water. Still, all of these systems would require extensive further evaluation prior to consideration of megatonne‐scale CO2 sequestration. Many key unknowns remain, including the partitioning of breakdown among sulfate‐reducing and methanogenic metabolisms and the fate of methane in the environment. Given the urgency of responsible CDR development and the potential for anoxic basins to reduce ecological risks to animal communities, efforts to address knowledge gaps related to microbial kinetics, benthic processes, and physical mixing in these systems are critically needed.

Microbial mediation of cryptic methane cycle in semiclosed marine water column

<p>The continuous expansion of oxygen minimum zones (OMZs) has promoted methane emissions, and the origin and fate of methane in semi enclosed OMZs are poorly understood. In this study, we sampled 21 water layers across a 300-m depth of the Yongle blue hole (YBH) located in the South China Sea for metagenomics and metatranscriptomics work, coupled with data from global anoxic/suboxic water columns. The 16S rDNA reads in the metagenomes indicate high percentages of unclassified prokaryotes (on average 38%) and high microbiome novelty scores in anoxic layers of YBH, which are significantly higher than other semiclosed oxygen minimum zones. Analyses of 318 draft genomes and functional genes indicate that the methane source of YBH probably resulted from microbial cleavage of methylphosphonate (MPn) and dimethylsulfoniopropionate (DMSP). Methane oxidation that prevents methane emission from YBH was probably conducted by a new group of anaerobic methanotrophic Planctomycetota, Bacteroidota, and Verrucomicrobiota in suboxic and anoxic environments of YBH, in addition to Methylococcales in oxic layers. The Bacteroidota solely contribute to ~77% of methane decline from the peak at 180 m depth. Our research casts light on the cryptic methane cycle mediated by the novel microbiome that controls the release of greenhouse gases from marine geographic depressions exemplified by YBH, offering valuable insights into mitigating climate change effects in marine environments.</p>

Fate of Methane from the Nord Stream Pipeline Leaks

Fate of Methane from the Nord Stream Pipeline Leaks

Fate of Methane Released From a Destroyed Oil Platform in the Gulf of Mexico

In 2004, destruction of a Gulf of Mexico oil platform by Hurricane Ivan initiated a discharge of oil and gas from a water depth of 135 m, where its bundle of well conductors was broken below the seafloor near the toppled wreckage. Discharge continued largely unabated until 2019, when findings partly reported herein prompted installation of a containment device that could trap oil before it entered the water column. In 2018, prior to containment, oil and gas bubbles formed plumes that rose to the surface, which were quantified by acoustic survey, visual inspection, and discrete collections in the water column. Continuous air sampling with a cavity ring-down spectrometer (CRDS) over the release site detected atmospheric methane concentrations as high as 11.7, ∼6 times greater than an ambient baseline of 1.95 ppmv. An inverse plume model, calibrated to tracer-gas release, estimated emission into the atmosphere of 9 g/s. In 2021, the containment system allowed gas to escape into the water at 120 m depth after passing through a separator that diverted oil into storage tanks. The CRDS detected transient peaks of methane as high as 15.9 ppmv ppm while oil was being recovered to a ship from underwater storage tanks. Atmospheric methane concentrations were elevated 1–2 ppmv over baseline when the ship was stationary within the surfacing plumes of gas after oil was removed from the flow. Oil rising to the surface was a greater source of methane to the atmosphere than associated gas bubbles.

Inter-Comparison of the Spatial Distribution of Methane in the Water Column From Seafloor Emissions at Two Sites in the Western Black Sea Using a Multi-Technique Approach

Understanding the dynamics and fate of methane (CH4) release from oceanic seepages on margins and shelves into the water column, and quantifying the budget of its total discharge at different spatial and temporal scales, currently represents a major scientific undertaking. Previous works on the fate of methane escaping from the seafloor underlined the challenge in both, estimating its concentration distribution and identifying gradients. In April 2019, the Envri Methane Cruise has been conducted onboard the R/V Mare Nigrum in the Western Black Sea to investigate two shallow methane seep sites at ∼120 m and ∼55 m water depth. Dissolved CH4 measurements were conducted with two continuous in-situ sensors: a membrane inlet laser spectrometer (MILS) and a commercial methane sensor (METS) from Franatech GmbH. Additionally, discrete water samples were collected from CTD-Rosette deployment and standard laboratory methane analysis was performed by gas chromatography coupled with either purge-and-trap or headspace techniques. The resulting vertical profiles (from both in situ and discrete water sample measurements) of dissolved methane concentration follow an expected exponential dissolution function at both sites. At the deeper site, high dissolved methane concentrations are detected up to ∼45 m from the seabed, while at the sea surface dissolved methane was in equilibrium with the atmospheric concentration. At the shallower site, sea surface CH4 concentrations were four times higher than the expected equilibrium value. Our results seem to support that methane may be transferred from the sea to the atmosphere, depending on local water depths. In accordance with previous studies, the shallower the water, the more likely is a sea-to-atmosphere transport of methane. High spatial resolution surface data also support this hypothesis. Well localized methane enriched waters were found near the surface at both sites, but their locations appear to be decoupled with the ones of the seafloor seepages. This highlights the need of better understanding the processes responsible for the transport and transformation of the dissolved methane in the water column, especially in stratified water masses like in the Black Sea.

Methane emission and methanotrophic activity in groundwater-fed drinking water treatment plants

Abstract Groundwater for drinking water production may contain dissolved methane (CH4) at variable concentrations. Most of this important greenhouse gas is often vented to the atmosphere during primary aeration and gas stripping processes at drinking water treatment plants (DWTPs). However, limited information exists regarding emission and fate of methane at many groundwater-fed DWTPs. This study estimates emission of methane from 1,004 DWTPs in Denmark and includes data from 3,068 groundwater wells. The fate of methane and occurrence of methane oxidizing bacteria in DWTPs was examined, including the potential role in ammonia removal. Methane emission from Danish DWTPs was estimated to be 1.38–2.95 × 10−4 Tg CH4/y which corresponds to 0.05–0.11% of the national anthropogenic methane emission. Trace levels of methane remained in the drinking water after primary aeration and entered the sand filters as a potential microbial substrate. Methanotrophic bacteria and active methane oxidation was always detected in the sand filters at groundwater-fed DWTPs. Methanotrophic consortia isolated from DWTP sandfilters were inoculated into laboratory-scale sand filters and the activity confirmed that methanotrophic consortia can play a role in the removal of ammonia via assimilation and co-oxidation. This suggests a potential for facilitating the removal of inorganic constituents from drinking water using methane as a co-substrate.

A geochemical and multi-isotope modeling approach to determine sources and fate of methane in shallow groundwater above unconventional hydrocarbon reservoirs

Due to increasing concerns over the potential impact of shale gas and coalbed methane (CBM) development on groundwater resources, it has become necessary to develop reliable tools to detect any potential pollution associated with hydrocarbon exploitation from unconventional reservoirs. One of the key concepts for such monitoring approaches is the establishment of a geochemical baseline of the considered groundwater systems. However, the detection of methane is not enough to assess potential impact from CBM and shale gas exploitation since methane in low concentrations has been found to be naturally ubiquitous in many groundwater systems. The objective of this study was to determine the methane sources, the extent of potential methane oxidation, and gas-water-rock-interactions in shallow aquifers by integrating chemical and isotopic monitoring data of dissolved gases and aqueous species into a geochemical PHREEQC model. Using data from a regional groundwater observation network in Alberta (Canada), the model was designed to describe the evolution of the concentrations of methane, sulfate and dissolved inorganic carbon (DIC) as well as their isotopic compositions (δ34SSO4, δ13CCH4 and δ13CDIC) in groundwater subjected to different scenarios of migration, oxidation and in situ generation of methane. Model results show that methane migration and subsequent methane oxidation in anaerobic environments can strongly affect its concentration and isotopic fingerprint and potentially compromise the accurate identification of the methane source. For example elevated δ13CCH4 values can be the result of oxidation of microbial methane and may be misinterpreted as methane of thermogenic origin. Hence, quantification of the extent of methane oxidation is essential for determining the origin of methane in groundwater. The application of this model to aquifers in Alberta shows that some cases of elevated δ13CCH4 values were due to methane oxidation resulting in pseudo-thermogenic isotopic fingerprints of methane. The model indicated no contamination of shallow aquifers by deep thermogenic methane from conventional and unconventional hydrocarbon reservoirs under baseline conditions. The developed geochemical and multi-isotopic model describing the sources and fate of methane in groundwater is a promising tool for groundwater assessment purposes in areas with shale gas and coalbed methane development.

Origin and fate of methane in the Eastern Tropical North Pacific oxygen minimum zone

Oxygen minimum zones (OMZs) contain the largest pools of oceanic methane but its origin and fate are poorly understood. High-resolution (<15 m) water column profiles revealed a 300 m thick layer of elevated methane (20–105 nM) in the anoxic core of the largest OMZ, the Eastern Tropical North Pacific. Sediment core incubations identified a clear benthic methane source where the OMZ meets the continental shelf, between 350 and 650 m, with the flux reflecting the concentration of methane in the overlying anoxic water. Further incubations characterised a methanogenic potential in the presence of both porewater sulphate and nitrate of up to 88 nmol g−1day−1 in the sediment surface layer. In these methane-producing sediments, the majority (85%) of methyl coenzyme M reductase alpha subunit (mcrA) gene sequences clustered with Methanosarcinaceae (⩾96% similarity to Methanococcoides sp.), a family capable of performing non-competitive methanogenesis. Incubations with 13C-CH4 showed potential for both aerobic and anaerobic methane oxidation in the waters within and above the OMZ. Both aerobic and anaerobic methane oxidation is corroborated by the presence of particulate methane monooxygenase (pmoA) gene sequences, related to type I methanotrophs and the lineage of Candidatus Methylomirabilis oxyfera, known to perform nitrite-dependent anaerobic methane oxidation (N-DAMO), respectively.

Fate of methane in aquatic systems dominated by free-floating plants

Worldwide the area of free-floating plants is increasing, which can be expected to alter methane (CH4) emissions from aquatic systems in several ways. A large proportion of the CH4 produced may become oxidized below the plants due to the accumulation of CH4 as a result of a decrease in the diffusive water-atmosphere flux and the entrapment of part of the ebullitive CH4, in combination with suitable conditions for methane oxidizing (MOX) bacteria in the aerobic rhizosphere. We used a set of essays to test this hypothesis and to explore the effect of different densities for three widespread free-floating species: Azolla filiculoides, Salvinia natans, and Eichhornia crassipes. The gas exchange velocity, proportion of CH4 bubbles trapped by the plants, occurrence of radial oxygen loss from roots, and MOX rates on the roots were assessed. We subsequently used the outcome of these experiments to parameterize a simple model. With this model we estimated the proportion of the produced CH4 that is oxidized, for different plant species and different densities. We found that in a shallow (1 m) system up to 70% of the CH4 produced may become oxidized as a result of a strong decrease in gas exchange combined with high MOX activity of the rhizosphere microbiome. As floating plants also are likely to increase CH4 production by organic matter production, especially when their presence induces anaerobic conditions, the overall effect on CH4 emission will strongly depend on local conditions. This explains the contrasting effects of floating plants on CH4 emissions in literature as reviewed here. As the effect of floating plants on CH4 emissions, including the high MOX rates we show here, can be substantial, there is an urgent need to consider this impact when assessing greenhouse gas budgets.

Three‐dimensional numerical simulations of methane gas migration from decommissioned hydrocarbon production wells into shallow aquifers

AbstractThree‐dimensional numerical simulations are used to provide insight into the behavior of methane as it migrates from a leaky decommissioned hydrocarbon well into a shallow aquifer. The conceptual model includes gas‐phase migration from a leaky well, dissolution into groundwater, advective‐dispersive transport and biodegradation of the dissolved methane plume. Gas‐phase migration is simulated using the DuMux multiphase simulator, while transport and fate of the dissolved phase is simulated using the BIONAPL/3D reactive transport model. Methane behavior is simulated for two conceptual models: first in a shallow confined aquifer containing a decommissioned leaky well based on a monitored field site near Lindbergh, Alberta, Canada, and secondly on a representative unconfined aquifer based loosely on the Borden, Ontario, field site. The simulations show that the Lindbergh site confined aquifer data are generally consistent with a 2 year methane leak of 2–20 m3/d, assuming anaerobic (sulfate‐reducing) methane oxidation and with maximum oxidation rates of 1 × 10−5 to 1 × 10−3 kg/m3/d. Under the highest oxidation rate, dissolved methane decreased from solubility (110 mg/L) to the threshold concentration of 10 mg/L within 5 years. In the unconfined case with the same leakage rate, including both aerobic and anaerobic methane oxidation, the methane plume was less extensive compared to the confined aquifer scenarios. Unconfined aquifers may therefore be less vulnerable to impacts from methane leaks along decommissioned wells. At other potential leakage sites, site‐specific data on the natural background geochemistry would be necessary to make reliable predictions on the fate of methane in groundwater.

Microbes Make a Quick Meal of Methane in a Submarine Canyon

Scientists track the fate of methane released by hydrates in a major canyon off the U.S. East Coast.

Anaerobic Metabolism in Tidal Freshwater Wetlands: III. Temperature Regulation of Iron Cycling

Understanding the ecological processes that regulate the production and fate of methane (CH4) in wetland soils is essential for forecasting wetland CH4 emissions. Iron reduction is an important carbon mineralization pathway that is capable of suppressing CH4 production in freshwater wetlands, but our understanding of temperature regulation of iron oxide respiration and the subsequent impacts on CH4 production is limited. We tested the hypothesis that temperature regulates iron reduction rates indirectly through differential effects on Fe(II) oxidation versus Fe(III) reduction, which ultimately determines the size of the microbially labile, poorly crystalline Fe(III) pool. Our study indicates that rates of iron reduction are more sensitive to changes in temperature than rates of iron oxidation, which creates imbalance in the relative proportion of Fe(II) and Fe(III) in the poorly crystalline soil iron pool as temperatures change. Our results suggest that warmer temperatures can cause the Fe(III) oxide pool to decline, limiting the Fe(III) supply to iron reducers and relieving competition for organic carbon with methanogens.

メタン循環に関わる海底下生命圏

Methane is one of the major end products from photosynthetic organic matter. Based on stable carbon and hydrogen isotopic compositions of methane, biological pathways mainly consisting of carbon dioxide reduction coupled to molecular hydrogen oxidation and acetate fermentation and abiological pathways such as thermal degradation of organic matter have been systematically classified. However, recent advances in subseafloor biosphere research have unveiled the complexity of processes involved in the transformation, migration and fate of methane. Particularly, it has been recognized that marine sediments with high flux of methane harbor novel lineages of microorganisms, the physiological traits of which are largely unknown due to their resistance to cultivation. In this review article, microbiological investigations that shed light on DNA-based microbial community structures and metabolic diversity and activity related to methane production and consumption in organic-rich marine sediments are briefly summarized.

Geochemical characterization, source, and fate of methane and hydrogen sulfide at the Belmont Learning Center, Los Angeles

This article examines environmental concerns at the site of a Los Angeles, California, high school known as Belmont Learning Center (BLC) during its construction. A part of the site on which the school was to be built is a largely depleted oil field in the center of Los Angeles, close to a heavily populated area. Located nearby are another high school and an elementary school, each constructed more than 70 yr ago atop the same oil field. Prior to and during construction at the BLC site, which began in 1990, methane (CH4) and hydrogen sulfide (H2S) were detected in deep soil borings and monitoring wells. After the building construction began, a stratigraphic offset was also detected and interpreted as a fault line, which could be traced beneath one of the nearly completed buildings. This resulted in a decision to demolish that building and an adjacent one and to temporarily suspend all construction activity. Additional analytical measurements showed that the highest concentrations of both CH4 (5% atmospheric concentration) and H2S (100 ppmv) occurred only in the deeper samples, and that only traces of these environmentally hazardous gases were present at or near the soil surface. In this article, we use carbon, hydrogen, and sulfur stable isotope data, as well as 14C measurements to describe the sources and natural processes of CH4 and H2S removal. The interpretations offered in this article will hopefully be useful in assisting environmental professionals and government officials who evaluate hazardous soil gas concentrations to make decisions during the process of issuing or denying construction permits.

The Mystery of Methane on Mars &amp; Titan

Of all the planets in the solar system other than Earth, Mars has arguably the greatest potential for life, either extinct or extant. It resembles Earth in so many ways: its formation process, its early climate history, its reservoirs of water, its volcanoes and other geologic processes. Microorganisms would fit right in. Another planetary body, Saturn’s largest moon Titan, also routinely comes up in discussions of extraterrestrial biology. In its primordial past, Titan possessed conditions conducive to the formation of molecular precursors of life, and some scientists believe it may have been alive then and might even be alive now. To add intrigue to these possibilities, astronomers studying both these worlds have detected a gas that is often associated with living things: methane. It exists in small but significant quantities on Mars, and Titan is literally awash with it. A biological source is at least as plausible as a geologic one, for Mars if not for Titan. Either explanation would be fascinating in its own way, revealing either that we are not alone in the universe or that both Mars and Titan harbor large underground bodies of water together with unexpected levels of geochemical activity. Understanding the origin and fate of methane on these bodies will provide crucial clues to the processes that shape the formation, evolution and habitability of terrestrial worlds in this solar system and possibly in others. Methane (CH4) is abundant on the giant planets—Jupiter, Saturn, Uranus and Neptune—where it was the product of chemical processing of primordial solar nebula material. On Earth, though, methane is special. Of the 1,750 parts per billion by volume (ppbv) of methane in Earth’s atmosphere, 90 to 95 percent is biological in origin. Grass-eating ungulates such as cows, goats and yaks belch out one fifth of the annual global methane release; the gas is a metabolic by-product of the bacteria in their guts. Other significant sources include termites, rice paddies, swamps, The Mystery of Methane on Mars & Titan

The fate of methane in a claus plant reaction furnace

AbstractExperimental kinetic data are reported for key side reactions occurring in the front end [i. e. the reaction furnace (RF) and the waste heat boiler (WHB)] of modified Claus plants used for sulfur recovery from the sour gases evolved in the treatment of natural gas. An extensive experimental study was conducted in a high temperature tubular reactor system for two important homogenous gas‐phase reactions. Firstly, experiments were carried out to study the oxidation of hydrogen sulfide and methane mixtures in the presence of oxygen. Secondly, the reaction between methane and sulfur dioxide was investigated experimentally. These results showed that methane was much less competitive for oxygen than hydrogen sulfide. Hence, in a partially oxidizing environment of a RF, data showed that methane reacted significantly with other major sulfur containing species, as secondary reactions, to form COS and especially CS2. This is highly problematic from an environmental point of view.

Simple Molecular Systems at Very High Pressures: Computer simulation studies.

We discuss the application of ab initio molecular dynamics simulations results to a variety of simple molecular systems under pressure. In particular we consider the polymerization and subsequent amorphization of C2H2 crystals upon compression up to 50 GPa, the determination of the ground state structure of the broken symmetry phase of H2 in the pressure range 100-150 GPa, the fate of methane and ammonia along the isentrope of the middle ice layers of Neptune. We also discuss preliminary applications to O2 and CO.

Fate of methane in the Hudson River and Estuary

Methane (CH4) concentrations and oxidation rates were measured throughout the Hudson River Estuary in March and August of 1991. Methane concentrations ranged from 50 to 940 nM and were supersaturated with respect to the atmosphere along the entire length of the river, with generally higher CH4 values in the lower, saline portion of the estuary. A seasonally averaged diffusive flux to the atmosphere from the Hudson River was estimated to be 5.6 mg CH4 m−2 d−1, corresponding to an annual flux of 0.76 × 109 g CH4. The Hudson River Estuary also releases approximately 0.2 × 109 g CH4 annually to nearshore marine waters. Diffusive flux across the air/river interface was the dominant removal mechanism for Hudson River CH4 in March. In August, CH4 oxidation was the dominant CH4 sink in freshwater and brackish (&lt;6‰) sections of the river, removing up to 70% of ambient CH4 per day compared to maximum daily removal rates of 13% in March. Thus methane oxidation can play a major role in limiting releases of CH4 to the atmosphere from rivers and other freshwater environments. Methane oxidation activity decreased rapidly as salinity increased, with less than 2% of ambient CH4 being oxidized per day at salinities greater than 25‰. Addition of NaCl or seawater to freshwater samples resulted in comparable inhibition of methanotrophic activity. Budget calculations showed that flux to the atmosphere and CH4 oxidation in March removed less water column CH4 than was supplied to the Hudson River over its entire length. In August, however, CH4 removal approximately equaled CH4 supply with the result that there was no net accumulation of CH4 over the length of the river.