CH4 Concentrations Research Articles

Effects of mimicking manure removal strategies on ammonia and greenhouse gas emissions in sow pen scale models

With growing concerns about air pollution and global warming effects, the emissions of NH3 and greenhouse gases (GHGs) have become significant issues in the pig production industry. In order to discover whether optimizing manure removal strategies could alter the manure decomposition process and benefit the reduction of gas emissions, a scale model approach was used to quantify the gas emissions under controlled conditions. This study compared the gas emission reduction potential of two classic manure removal systems (scraper and pull-plug system) in three manure removal strategies: scraper-I (retaining manure for 24 h), scraper-II (retaining manure for 8 and 16 h) and pull-plug (retaining manure for 44 days). Fresh urine and faeces collected from a gestation sow house were applied to the scale models and then removed through the manure removal systems. The concentrations of gases (NH3, CH4, CO2, and N2O) within the scale model and removed slurry samples were collected and analysed (pH, electric conductivity, dry matter, total nitrogen, total ammonium nitrogen and total carbon). The results showed that emissions of CH4, CO2, and N2O from scraper-I were on average 54%, 56% and 25% lower than those from scraper-II, and 71%, 67% and 6% lower than those from pull-plug treatment, respectively. The GHGs emission rates (as CO2-equivalents) of scraper-I and scraper-II were 52% and 26.3% lower than that of pull-plug treatment respectively (P < 0.01). The emissions of NH3 displayed a temporary peak during each application of urine and removal of manure. In pull-plug treatment, the concentrations of NH3, CH4, and CO2 exponentially increased between Day 39 and Day 41. The nitrogen content, both total nitrogen and total ammonium nitrogen, within the slurry under the scraper system exhibited lower values compared to those from the pull-plug system. Conversely, the total carbon content was higher in the former system. Caution is warranted in extrapolating results to full-scale pig housing, given study limitations (e.g. small scale, mimicked scraper activity, no animals, etc.). Nevertheless, the conclusions and findings of this study provide fundamental data for understanding gas emissions from pig house manure management. This insight can guide the design and daily operations of low-emission manure removal systems in gestation sow houses.

Potential of Methane (CH4), Nitrogen (N2), and Carbon Dioxide (CO2) from Eco-Enzyme with the Addition of Cow Feces Starter

Eco-enzyme solutions are generally used in the manufacture of disinfectants, floor cleaners, liquid fertilizers, preservatives and others. In this study, eco-enzyme was used as the main ingredient in the manufacture of biogas fermentation with the addition of cow feces as an additional starter in the fermentation. The aim of this study was to determine the content of CH4, CO2, N2, pH, temperature, and pressure in eco-enzyme fermentation with the addition of cow feces starter. his research is a quantitative research with the type of experimental research as well as direct observation data collection techniques and data analysis techniques using descriptive statistical analysis. The results showed that the treatment that produced the highest methane (CH4) gas was the P5 treatment with a concentration of 2.889%. 6,1. The highest volume pressure value was produced in the P5 treatment which was 70 ml. Nitrogen gas (N2) and carbon dioxide gas (CO2), the concentration of nitrogen gas (N2) from reactor P0 - P4 is in the range of 95.875-99.669 % and the concentration of carbon dioxide (CO2) from reactor P0 - P4 is in the range of 0.237 - 4.125 %.

Organic Matter Accumulation and Hydrology as Drivers of Greenhouse Gas Dynamics in Newly Developed Artificial Channels.

Artificial channels, common features of inland waters, have been suggested as significant contributors to methane (CH4) and carbon dioxide (CO2) dynamics and emissions; however, the magnitude and drivers of their CH4 and CO2 emissions (diffusive and ebullitive) remain unclear. They are characterized by reduced flow compared to the donor river, which results in suspended organic matter (OM) accumulation. We propose that in such systems hydrological controls will be reduced and OM accumulation will control emissions by promoting methane production and outgassing. Here, we monitored summertime CH4 and CO2 concentrations and emissions on six newly constructed river-fed artificial channels, from bare riparian mineral soil to lotic channels, under two distinct flow regimes. Chamber-based fluxes were complemented with hydrology, total fluxes (diffusion + ebullition), and suspended OM accumulation assessments. During the first 6 weeks after the flooding, inflowing riverine water dominated the emissions over in-channel contributions. Afterwards, a substantial accumulation of riverine suspended OM (≥50% of the channel's volume) boosted in-channel methane production and led to widespread ebullition 10× higher than diffusive fluxes, regardless of the flow regime. Our finding suggests ebullition as a dominant pathway in these anthropogenic systems, and thus, their impact on regional methane emissions might have been largely underestimated.

Evaluation of biogas production and bacterial load from co‐digestion of chicken manure with different types of household waste

AbstractBackgroundThe aim of this study was to evaluate the biogas production of chicken manure (CM) co‐digestion with different types of household waste (soft organic [SO] and food waste [FW]), as well as to evaluate the bacterial load of feeding stock and digested slurry samples before and after anaerobic digestion (AD). The experiment was carried out using lab‐based prototype digesters for co‐digestion of CM with different household wastes (5%). Three experimental groups (T1, T2, and T3) were designed using mixing ratios of SO:CM:H2O:inoculum (5:22.5:22.5:50), FW:CM:H2O:inoculum (5:22.5:22.5:50), and (SO + FW):CM:H2O:inoculum (2.5 + 2.5:22.5:22.5:50). The digesters were set at 28–34°C for 30 days for hydraulic retention time (HRT). Total viable count (TVC), Escherichia coli, and Salmonella spp. counts were determined using the spread plate technique.ResultsThe study revealed that the highest average cumulative biogas yield was achieved from T1 &gt; T3 &gt; T2, but the concentration of CH4 was found in T3 &gt; T2 &gt; T1. The biogas production between the three groups was statistically nonsignificant (p &gt; 0.05) but the daily concentration of CH4 was found statistically significant (p &lt; 0.05). The average concentration of CH4 and CO2 in biogas was found to be 30% and 68% for T1, 60% and 37% for T2, and 69% and 27% for T3. However, the H2S content was within the acceptable range. The bacterial load was decreased by 2–3 logs before and after AD, and this reduction was statistically significant (p &lt; 0.05).ConclusionThe research found that the co‐digestion of CM with combined household wastes increased the methane concentration in biogas.

Recycled by leaf inhabitants: Terrestrial bacteria drive the mineralization of organic matter in lake water

AbstractTerrestrial organic matter subsidizes aquatic food webs and plays an important role in carbon cycling in lake ecosystems, where it is decomposed mainly by microbes. However, the contribution of terrestrial and aquatic microbiomes on terrestrial carbon cycling and their effects on the biochemical fate of carbon has remained understudied. Therefore, we explored the microbial carbon utilization of three chemically differing leaf species in lake water in microcosms and quantified the biochemical endpoints of leaf carbon in CO2, CH4, and microbial biomass. Additionally, we identified microbial taxa responsible for leaf carbon recycling and studied the role of epiphytic and endophytic leaf microbiomes in microbial community succession in lake water. Microbially utilized leaf carbon was mainly respired (82.7 ± 1.4%), whereas a small proportion (17.1 ± 1.4%) was assimilated into biomass. Carbon from nitrogen‐rich alder leaves was taken up at the fastest rate, whereas birch leaf addition produced the highest concentrations of CH4, suggesting that leaf chemistry affects the decomposition rate and biochemical fate of carbon. In particular, terrestrial bacteria shaped the succession of aquatic bacterial communities. The addition of leaves resulted in the equal contribution of epiphytic and endophytic bacteria in the lake water, whereas epiphytic fungi dominated the fungal community structure. Our results suggest that terrestrial bacteria originating from terrestrial leaves influence the microbiome succession in lake ecosystems and play a key role in linking terrestrial carbon to an aquatic food web and determining the quality of carbon emissions that are released into the atmosphere.

Commissioning of Upgrades to T6 to Study Giant Planet Entry

The scientific potential of a mission to the ice giants is well recognized and has been identified by NASA and ESA as a high priority on several occasions, most recently in the 2023–2032 Decadal Survey. The payload capacity of such a spacecraft is limited by the heat shield thickness, which must be sized conservatively due to a lack of reliable data for convective and radiative heat flux along the proposed entry trajectories. Major upgrades to the Oxford T6 Stalker Tunnel have been commissioned that allow study of giant planet entry trajectories, including a flammable gas handling system, a Mach 10 expansion nozzle, and a steel shock tube with optical access. Initial testing has been completed in shock tube and expansion tunnel modes, with peak shock speeds of 18.9 km/s achieved. Convective heat flux and surface pressure were measured at several locations on a 45° sphere cone model in expansion tunnel mode. Measurements of the radiating shock layer were made in shock tube mode to assess the effect of CH4 concentration. This work establishes the first high-enthalpy giant planet entry test bed in Europe.

Effect of Trimebutine and Rifaximin on Breath Hydrogen and Methane by Glucose Breath Test in Patients With Functional Bloating: A Randomized Double-blind Clinical Trial.

Drugs that stabilize intestinal motility may improve the efficacy of nonabsorbable antibiotics, such as rifaximin, against small intestinal bacterial overgrowth (SIBO). We compared the efficacy of rifaximin alone with that of its combination with trimebutine maleate against SIBO. We performed a randomized double-blind placebo-controlled trial (https://cris.nih.go.kr, no. KCT0004836) that included patients with functional bloating, no constipation, and SIBO using the hydrogen (H2)-methane (CH4) glucose breath test (GBT). Patients were randomized into 2 groups in a 1:1 ratio, namely rifaximin (1200 mg/day) + trimebutine maleate (600 mg/day) group and rifaximin + placebo group, for 2 weeks. Patients completed a symptom questionnaire and underwent a GBT at baseline and at 1 month after treatment withdrawal. The primary outcome was SIBO eradication. The secondary outcomes included changes in the concentrations of exhaled gases, symptoms, and presence of adverse events. The complete eradication rate of SIBO was 35.9% (14/39) in the rifaximin group, and 34.1% (14/41) in the combined group with no significant differences. In both groups, no significant differences were observed in GBT profiles before and after the treatment, respectively. However total breath H2 and CH4 concentration were conspicuously decreased in the combined group after treatment. The combined group exhibited substantial relief of bloating. The adverse events were similar in the 2 groups. While the combination therapy was not superior over rifaximin alone for SIBO eradication, it improves the symptom of bloating with numerically reducing the concentration of breath H2/CH4.

Factor analysis and countermeasures for global warming based on data science methods

In recent years, the frequent and intensifying occurrence of extreme weather events such as heatwaves, floods, and storms worldwide has led scientists and policymakers to be increasingly concerned about the phenomenon of global warming. The global average temperature has steadily risen over the past few decades, and 2015-2022 has been identified as the warmest years on record. Taking global warming as the research object, the main problem is to find out the factors affecting climate change. The article predicts the global average temperature of the future and builds a model to analyse the relationship between global average temperature, time, location and the factors affecting climate change. The prediction models of ARMIA and EEMD-LSTM were built, and the model with the best fit was obtained after several iterations of tuning and trial optimization. The results showed that Flood, Storm, and Extreme temperature, had a high correlation with the global average temperature. The data of greenhouse gas indicators such as CO2, NO, and CH4, and catastrophes such as earthquakes, Volcanic activity, and wildfires have objective effects on global warming. Random forest regression model pairs were developed, and analysis of the importance of each component to the model showed that CO2 concentration and CH4 concentration had significant effects on global average temperature. Propose measures that can curb or slow down global warming.

Multiple stressors alter greenhouse gas concentrations in streams through local and distal processes.

Streams are significant contributors of greenhouse gases (GHG) to the atmosphere, and the increasing number of stressors degrading freshwaters may exacerbate this process, posing a threat to climatic stability. However, it is unclear whether the influence of multiple stressors on GHG concentrations in streams results from increases of in-situ metabolism (i.e., local processes) or from changes in upstream and terrestrial GHG production (i.e., distal processes). Here, we hypothesize that the mechanisms controlling multiple stressor effects vary between carbon dioxide (CO2) and methane (CH4), with the latter being more influenced by changes in local stream metabolism, and the former mainly responding to distal processes. To test this hypothesis, we measured stream metabolism and the concentrations of CO2 (pCO2) and CH4 (pCH4) in 50 stream sites that encompass gradients of nutrient enrichment, oxygen depletion, thermal stress, riparian degradation and discharge. Our results indicate that these stressors had additive effects on stream metabolism and GHG concentrations, with stressor interactions explaining limited variance. Nutrient enrichment was associated with higher stream heterotrophy and pCO2, whereas pCH4 increased with oxygen depletion and water temperature. Discharge was positively linked to primary production, respiration and heterotrophy but correlated negatively with pCO2. Our models indicate that CO2-equivalent concentrations can more than double in streams that experience high nutrient enrichment and oxygen depletion, compared to those with oligotrophic and oxic conditions. Structural equation models revealed that the effects of nutrient enrichment and discharge on pCO2 were related to distal processes rather than local metabolism. In contrast, pCH4 responses to nutrient enrichment, discharge and temperature were related to both local metabolism and distal processes. Collectively, our study illustrates potential climatic feedbacks resulting from freshwater degradation and provides insight into the processes mediating stressor impacts on the production of GHG in streams.

Gasification of Liquid Hydrocarbon Waste by the Ultra-Superheated Mixture of Steam and Carbon Dioxide: A Thermodynamic Study

The thermodynamic modeling of waste oil (WO) gasification by a high-temperature gasification agent (GA) composed of an ultra-superheated H2O/CO2 mixture is carried out. The GA is assumed to be obtained by the gaseous detonation of fuel–oxidizer–diluent mixture in a pulsed detonation gun (PDG). N-hexadecane is used as a WO surrogate. Methane or the produced syngas (generally a mixture of H2, CO, CH4, CO2, etc.) is used as fuel for the PDG. Oxygen, air, or oxygen-enriched air are used as oxidizers for the PDG. Low-temperature steam is used as a diluent gas. The gasification process is assumed to proceed in a flow-through gasifier at atmospheric pressure. It is shown that the use of the detonation products of the stoichiometric methane–oxygen and methane–air mixtures theoretically leads to the complete conversion of WO into a syngas consisting exclusively of H2 and CO, or into energy gas with high contents of CH4 and C2-C3 hydrocarbons and an LHV of 36.7 (fuel–oxygen mixture) and 13.6 MJ/kg (fuel–air mixture). The use of the detonation products of the stoichiometric mixture of the produced syngas with oxygen or with oxygen-enriched air also allows theoretically achieving the complete conversion of WO into syngas consisting exclusively of H2 and CO. About 33% of the produced syngas mixed with oxygen can be theoretically used for PDG self-feeding, thus making the gasification technology very attractive and cost-effective. To self-feed the PDG with the mixture of the produced syngas with air, it is necessary to increase the backpressure in the gasifier and/or enrich the air with oxygen. The addition of low-temperature steam to the fuel–oxygen mixture in the PDG allows controlling the H2/CO ratio in the produced syngas from 1.3 to 3.4.

Experimental study and modeling of the liquid phase hydrogenation of acetylene

Selective hydrogenation of acetylene is an important process for both ethylene purification and ethylene production from acetylene in the industry. Herein, we proposed liquid phase acetylene hydrogenation for high feed concentrations of C2H2 (8 %) and CO (20 %), which is used to produce ethylene as a subsequent process of partial oxidation of natural gas. The experiments were carried out in a stirred tank reactor using N-methylpyrrolidone (NMP) as solvent and PdAg/SiO2 as catalyst. The liquid phase process obtained a much higher selectivity to ethylene (92 %) with only 8 % selectivity to green oil (GO) and C4, compared to 71 % ethylene selectivity in gas phase hydrogenation. Furthermore, in the liquid phase ethylene selectivity increased with increasing acetylene conversion, especially in the conversion range of 80–100 %. We developed a model incorporating reaction kinetics, mass transfer and reactor model to predict the acetylene conversion and ethylene selectivity in liquid phase hydrogenation. The calculation results indicated that hydrogenation in the liquid phase operated at a lower acetylene concentration and a higher H2/C2H2 ratio, especially under high acetylene conversions. This explains why the liquid phase hydrogenation of acetylene has a much higher selectivity to ethylene than the gas phase process.

Potential climates and habitability on Gl 514 b: a super-Earth exoplanet with high eccentricity

ABSTRACT The recently discovered super-Earth Gl 514 b, orbiting a nearby M0.5-1.0 star at 7.6 pc, is one of the best benchmark exoplanets for understanding the potential climate states of eccentric planets. The elongated (e = 0.45$^{+0.15}_{-0.14}$) orbit of Gl 514 b, which only partially lies in the Conservative Habitable Zone, suggests a dynamically young system, where the spin-orbit tidal synchronization may not have yet occurred up to the present time. In the present work, we use a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the potential impact of both constrained and unconstrained planetary, orbital, and atmospheric parameters on the Gl 514 b habitability, mapped in terms of surface temperature. We test three distinct CO2-dominated atmospheres by varying the CH4 concentration values (0 per cent, 0.1 per cent, and 1 per cent) and the total surface pressure. As a general trend, we find that habitable conditions are favoured by high-CH4 and high-pressure regimes. Habitability also increases for high-axis obliquities (at least until the appearance of an icebelt), long-rotation periods, and high-ocean fractional coverage. If the ocean fraction is low, then also the argument of periastron becomes relevant. Our results are robust against changes of the continental distribution. Thus, we conclude that Gl 514 b can potentially maintain temperate surface conditions with modest seasonal temperature variations under a wide variety of planetary, orbital, and atmospheric conditions. Despite no transit have been detected yet, the results found in this work should motivate the community to invest time in future observations.

Experimental Study on Enhanced Methane Detection Using an MEMS-Pyroelectric Sensor Integrated with a Wavelet Algorithm.

An optical sensing approach that balances portability with cost efficiency has been designed for the reliable monitoring of fugitive methane (CH4) emissions. Employing a LiTaO3-based pyroelectric detector integrated with micro-electro-mechanical systems and a broad infrared source, the developed gas sensor adeptly measured CH4 concentrations with a low limit of detection of about 5.6 ppmv and showed rapid response times with t90 consistently under 3 s. Notably, the novelty of our method lies in its precise control and reduction of CH4 levels, enhanced by wavelet denoising. This technique, optimized through meticulous grid search, effectively mitigated noise interference noticeable at CH4 levels below 10 ppmv. Postdenoising, nonlinear regression analyses based on the modified Beer-Lambert equation returned R2 values of 0.985 and 0.982 for the training and validation sets, respectively. In conclusion, this gas sensor has been shown to be able to meet the requirements for early warning of CH4 leakage on the surface in various carbon capture, utilization, and storage projects such as enhanced oil or gas recovery projects using CO2 injection.

Cost modeling of photocatalytic decomposition of atmospheric methane and nitrous oxide

Abstract The photocatalytic decomposition of atmospheric methane (CH4) and nitrous oxide (N2O) could be valuable tools for mitigating climate change; however, to date, few photocatalyst deployment strategies have had their costs modeled. Here, we construct basic cost models of three photocatalytic CH4 and N2O decomposition systems: 1) a ground-based solar system with natural airflow over photocatalyst-painted rooftops, 2) a ground-based LED-lit system with fan-driven airflow, and 3) an aerosol-based solar system on solid particles dispersed in the atmosphere. Each model takes as inputs the photocatalyst’s apparent quantum yield (AQY; a measure of how efficiently photons drive a desired chemical reaction) and the local CH4 or N2O concentration. Each model calculates an overall rate of greenhouse gas drawdown and returns a levelized cost of greenhouse gas removal per equivalent ton of carbon dioxide (tCO2e). Based on prior studies of atmospheric carbon dioxide removal, we adopt $100/tCO2e as a target cost.&amp;#xD;&amp;#xD;We estimate that painting rooftops with photocatalysts might meet the target cost for decomposition of &gt;10ppm CH4 with catalyst AQYs &gt;4%. If painting and cleaning costs were reduced by a factor of ~3 from our scenario, removal of ambient CH4 could meet the cost target with AQYs &gt;1% and removal of ambient N2O could do so with AQYs &gt;0.1%. &amp;#xD;Fan-driven systems with LED illumination appear to be very challenging, achieving removal costs &lt;$100/tCO2e only for AQYs of &gt;10% for CH4 and &gt;1% for N2O. Dispersing photocatalytic aerosols in the troposphere could be cost-effective with AQYs of &gt;0.4% for ambient CH4 or &gt;0.04% for ambient N2O. However, the mass of aerosols required is large and their side effects and social acceptability are uncertain. We note that, for any system, AQYs on the order of 1% will likely be extremely challenging to achieve with such dilute reagents.

Enhancing biomethane quality via the activation of natural zeolite from Lombok Island

&lt;p&gt;This study presents the results of the biogas purification test using the fixed-bed column method. As an adsorbent, natural zeolite from the Lombok island Indonesia was used. Zeolite is used for the purpose of purifying biogas produced from the anaerobic digestion (AD) process. To enhance the adsorption capacity, the zeolite underwent activation using distinct strong base and acid solutions—potassium hydroxide (KOH) and hydrochloric acid (HCl)—with concentrations of 10%, 15%, and 20%, individually. The experiment was carried out until the adsorbent reached saturation, at which point the methane (CH4) concentration began to decline. It was revealed that the typical Lombok zeolite showed good performance in increasing the concentration of CH4 in biogas. Furthermore, zeolites work better when activated with strong base solutions and at high concentrations. This is indicated by the achievement of higher CH4 concentrations and a longer saturation time. The results from analyzing zeolite features and pore characteristics indicate that acidic and base compounds yield distinct outcomes in terms of the surface structure of zeolite pores.&lt;/p&gt;

Development and machine learning-based calibration of low-cost multiparametric stations for the measurement of CO2 and CH4 in air

The pressing issue of atmospheric pollution has prompted the exploration of affordable methods for measuring and monitoring air contaminants as complementary techniques to standard methods, able to produce high-density data in time and space. The main challenge of this low-cost approach regards the in-field accuracy and reliability of the sensors. This study presents the development of low-cost stations for high-time resolution measurements of CO2 and CH4 concentrations calibrated via an in-field machine learning-based method. The calibration models were built based on measurements parallelly performed with the low-cost sensors and a CRDS analyzer for CO2 and CH4 as reference instrument, accounting for air temperature and relative humidity as external variables.To ensure versatility across locations, diversified datasets were collected, consisting of measurements performed in various environments and seasons. The calibration models, trained with 70 % for modeling, 15 % for validation, and 15 % for testing, demonstrated robustness with CO2 and CH4 predictions achieving R2 values from 0.8781 to 0.9827 and 0.7312 to 0.9410, and mean absolute errors ranging from 3.76 to 1.95 ppm and 0.03 to 0.01 ppm, for CO2 and CH4, respectively. These promising results pave the way for extending these stations to monitor additional air contaminants, like PM, NOx, and CO through the same calibration process, integrating them with remote data transmission modules to facilitate real-time access, control, and processing for end-users.

Simultaneous biogas upgrading and single cell protein production using hydrogen oxidizing bacteria

CO2, a primary byproduct of anaerobic digestion, significantly reduces the calorific value of biogas, necessitating its enhancement through biogas upgrading to increase the CH4 content. The hydrogen oxidizing bacteria (HOB) Cupriavidus necator H16 demonstrates potential as a candidate for biological biogas upgrading due to its efficient CO2 capture and biosynthesis capabilities. Results indicated that in batch experiments, the concentration of CH4 could be elevated from 57.09 % to 98.46 % within 72 h by HOB, with a maximum CO2 assimilation efficiency of 27 mL/(L·h), meeting the requirements for biomethane. In bioreactor scale-up experiments, the CH4 concentration was increased to 94.22 % within 96 h. Beyond biogas upgrading, HOB also produces biomass usable as single cell protein (SCP), with its protein content varying between 43.75–70.83 % depending on the gas supply ratio. A total of 17 amino acids were identified, including eight essential amino acids. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) indicated that the essential amino acid content in the HOB-based protein was well-balanced, closely approximating the quality of fishmeal and pork. A techno-economic analysis revealed that the net revenue from the anaerobic digestion process could be enhanced by 48.49 % using HOB-based biogas upgrading. In contrast, biogas upgrading processes based on hydrogenotrophic methanogens (HM) resulted in a 57 % reduction in net revenue. This study establishes a carbon flow pathway from organic solid waste to biomethane and utilizable protein sources, facilitating sustainable nutrient recovery. This approach not only enhances economic benefits but also reduces carbon emissions associated with the anaerobic digestion process.

Insight into the mechanism of helium enrichment in natural gas from the Bohai Bay basin, China: Chemical and isotopic composition perspectives

Helium (He) is an important societal resource, yet its enrichment mechanism is unclear in the Bohai Bay Basin, despite the presence of He-rich (He > 0.1% v/v) gas. A comprehensive analysis of 112 sets of chemical and isotopic data from natural gases in the literature was conducted to further elucidate the source and accumulation mechanism of He in this basin. Natural gas is categorized into five groups based on CO2 and N2 abundances: N2 gas (CO2+N2 ≥ 95%, CO2 < N2), high-purity CO2 gas (CO2+N2 ≥ 95%, CO2 > N2), low-purity CO2 gas (50 ≤ CO2+N2 < 95%, CO2 > N2), low-purity HC gas (15 ≤ CO2+N2 < 50%) and high-purity HC gas (CO2+N2 < 15%). δ13C–CO2 (−8.3 to −3.0‰) and 3He/4He (1.66–6.45 Ra, where Ra is the atmospheric 3He/4He) suggest a mantle origin of CO2 in N2 and CO2 gases. The δ13C–CO2 of N2 gas (−8.3‰) is lighter than that of high-purity CO2 gas (−6.2 to −3.4‰), indicating CO2 dissolution and mineralization. A positive correlation between He and CH4 content in the N2 and high-purity CO2 gases suggests water-derived CH4 capture during CO2 migration. Similarly, the positive correlation between He and N2 content across all samples indicates water-derived N2 capture during gas migration. A mixture of mantle and crust-derived He is indicated by 3He/4He ratio (0.06–6.45 Ra). Two distinct types of He-rich gas were identified: He-rich N2 gas (3He/4He = 3.1–3.2 Ra) and He-rich HC gas (3He/4He = 0.36–0.48 Ra). He enrichment in N2 gas is attributed to water-derived He capture and concurrent loss of CO2 during mantle-derived CO2 migration. He-rich HC gas formation results from He-rich N2 gas dilution with hydrocarbons. The findings provide theoretical support for exploring He-rich natural gas in this basin and offer valuable insights into He enrichment mechanisms in comparable sedimentary basins globally.

Dynamics of methane emissions from northwestern Gulf of Mexico subtropical seagrass meadows

While seagrass meadows are perceived to be pertinent blue carbon reservoirs, they also potentially release methane (CH4) into the atmosphere. Seasonal and diurnal variations in CH4 emissions from a subtropical hypersaline lagoon dominated by Halodule wrightii in southern Texas, USA, on the northwest coast of the Gulf of Mexico were investigated. Dissolved CH4 concentrations decreased in the daytime and increased overnight during the diel observation period, which could be explained by photosynthesis and respiration of seagrasses. Photosynthetic oxygen was found to significantly reduce CH4 emissions from seagrass sediment. Diffusive transport contributed slightly to the release of CH4 from the sediment to the water column, while plant mediation might be the primary mechanism. The diffusive CH4 flux at the sea-air interface was 12.3–816.2 µmol/m2 d, over the range of the sea-air fluxes previously reported from other seagrass meadows. This was related to relatively higher dissolved CH4 concentrations (11.6–258.2 nmol/L) in a mostly closed lagoon with restricted water exchange. This study emphasizes seagrass meadows in the subtropical hypersaline lagoon as a source of atmospheric CH4, providing insights into the interactions between seagrass ecosystems and methane dynamics, with potential implications for seagrass meadow management and conservation efforts.

Geochemical Characteristics and Geological Significance of Coalbed Methane in Suzhou Mining Area of the Huaibei Coalfield.

In this study, gas contents, geochemical features, and origins of coalbed methane (CBM) and their influence factors were investigated on nos. 7 and 8 CBM reservoirs from the Suzhou mining area of the Huaibei coalfield. Results have shown that the selected CBM reservoirs are characterized by various thickness (0.50-9.19 m) and buried depth (619-1226 m), but have relatively better lithology of surrounding rocks. Coal samples have similar maturity (Ro,max = 0.71-1.05%), but show differences in chemical composition and macerals. Gas content of nos. 7 and 8 CBM reservoirs ranges from 6.13-12.25 m3/t, but the value of former is lower than that of later one overall. In addition, CH4 is a predominantly component with a value of 88.23-99.00% (avg. 96.69%), and the heavy hydrocarbon gas (C2+) is 0.00-1.93% (avg. 0.41%). The δ13CCH4 value ranges from -64.54 to -46.36‰ (avg. -53.92‰), and the δ13DCH4 value is -224.36 to -211.75‰ (avg. -219.09‰). Based on the analysis of components and isotopic values, the CBM samples are thermogenic (20.92-71.30%; avg 50.09%) and secondary biogenic gases (28.70-74.49%; avg. 49.91%). Gas content shows changeable characteristics at a buried depth of 300-1300 m, which is affected by buried depth, reservoir temperature and pressure, Mad and vitrinite. However, the CH4 concentration shows no correlation with buried depth. Moreover, the buried depth is significantly positively correlated to δ13CCH4 and δ13DCH4. Based on the relationship between gas content and isotope values, it suggests that δ13CCH4 or δ13DCH4 may have a relationship with the main controlling factors of gas content.