The concentration of molecular H2 and CH4 in the stratosphere

Stratospheric profiles of CH₄ and H₂ over eastern Texas have been derived up to 31 km altitude from air samples collected aboard a balloon and analyzed by gas chromatography. For H₂, contamination during flight and measurement presented a problem which has been resolved only recently. The earlier profiles require corrections which are rather large for the highest altitudes.The three profiles indicate an increase of the H₂ concentration in the lower stratosphere from about 0.5 p.p.m. per volume at the tropopause to about 0.8 p.p.m. at around 27 km altitude. Above that altitude the H₂ concentration decreases again. An air sample collected between 44 and 62 km by a rocket-borne cryogenic sampler had an H₂ concentration of 0.4 p.p.m.The five CH₄ profiles showed a decrease in CH₄ concentration with altitude generally with a steeper gradient directly above the tropopause and a weaker gradient at higher altitudes reaching 0.9 p.p.m. at 30 km altitude. The CH₄ concentration in the rocket sample was 0.25 p.p.m., in good agreement with the gradient obtained from the balloon samples.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A Stream‐Based Methane Monitoring Approach for Evaluating Groundwater Impacts Associated with Unconventional Gas Development

Gaining streams can provide an integrated signal of relatively large groundwater capture areas. In contrast to the point‐specific nature of monitoring wells, gaining streams coalesce multiple flow paths. Impacts on groundwater quality from unconventional gas development may be evaluated at the watershed scale by the sampling of dissolved methane (CH₄) along such streams. This paper describes a method for using stream CH₄ concentrations, along with measurements of groundwater inflow and gas transfer velocity interpreted by 1‐D stream transport modeling, to determine groundwater methane fluxes. While dissolved ionic tracers remain in the stream for long distances, the persistence of methane is not well documented. To test this method and evaluate CH₄ persistence in a stream, a combined bromide (Br) and CH₄ tracer injection was conducted on Nine‐Mile Creek, a gaining stream in a gas development area in central Utah. A 35% gain in streamflow was determined from dilution of the Br tracer. The injected CH₄ resulted in a fivefold increase in stream CH₄ immediately below the injection site. CH₄ and δ¹³C_CH4 sampling showed it was not immediately lost to the atmosphere, but remained in the stream for more than 2000 m. A 1‐D stream transport model simulating the decline in CH₄ yielded an apparent gas transfer velocity of 4.5 m/d, describing the rate of loss to the atmosphere (possibly including some microbial consumption). The transport model was then calibrated to background stream CH₄ in Nine‐Mile Creek (prior to CH₄ injection) in order to evaluate groundwater CH₄ contributions. The total estimated CH₄ load discharging to the stream along the study reach was 190 g/d, although using geochemical fingerprinting to determine its source was beyond the scope of the current study. This demonstrates the utility of stream‐gas sampling as a reconnaissance tool for evaluating both natural and anthropogenic CH₄ leakage from gas reservoirs into groundwater and surface water.     

Methane Oxidation in the Water Column of Xiangxi Bay,Three Gorges Reservoir

Four field campaigns are carried out to quantify the methane (CH₄) oxidation rate in Xiangxi Bay (XXB) of the Three Gorges Reservoir (TGR), China. The water depth of the sampling site varied from 13 to 30 m resulting from the water level fluctuation of the TGR. The CH₄ oxidation rates are measured in situ as the decline of dissolved CH₄ concentration versus time in incubated, and those rates. The CH₄ oxidation rates range from 1.18 × 10^?3 to 3.69 × 10^?3 µmol L^?1 h^?1, with higher values and stronger variation during summer. A static floating chamber method is used to measure CH₄ emitted to the atmosphere resulting in an annual mean flux of 4.79 µmol m^?2 h^?1. The CH₄ emission rate is significantly negatively correlated with the water level. The results show that a large fraction of CH₄ is consumed in the water column with a range of 28.97–55.90 µmol m^?2 h^?1, accounting for ≈69–98% of the total CH₄ input into the water column, and more than 90% is consumed outside the summer, when the water level is lowest. Water depth, which is dominated by water level of the TGR, is a potentially important driver for CH₄ oxidation and atmospheric emission in the tributary bay.     

Impacts of Methane on Carbon Dioxide Storage in Brine Formations

In the context of geological carbon sequestration (GCS), carbon dioxide (CO₂) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH₄). In this multicomponent multiphase displacement process, CO₂ competes with CH₄ in terms of dissolution, and CH₄ tends to exsolve from the aqueous into a gaseous phase. Because CH₄ has a lower viscosity than injected CO₂, CH₄ is swept up into a ‘bank’ of CH₄‐rich gas ahead of the CO₂ displacement front. On the one hand, this may provide a useful tracer signal of an approaching CO₂ front. On the other hand, the emergence of gaseous CH₄ is undesirable because it poses a leakage risk of a far more potent greenhouse gas than CO₂ if the cap rock is compromised. Open fractures or faults and wells could result in CH₄ contamination of overlying groundwater aquifers as well as surface emissions. We investigate this process through detailed numerical simulations for a large‐scale GCS pilot project (near Cranfield, Mississippi) for which a rich set of field data is available. An accurate cubic‐plus‐association equation‐of‐state is used to describe the non‐linear phase behavior of multiphase brine‐CH₄‐CO₂ mixtures, and breakthrough curves in two observation wells are used to constrain transport processes. Both field data and simulations indeed show the development of an extensive plume of CH₄‐rich (up to 90 mol%) gas as a consequence of CO₂ injection, with important implications for the risk assessment of future GCS projects.     

The determination of deep temperatures by means of the CO-CO2-H2-H2O geothermometer: an example using fumaroles in the Campi Flegrei,Italy

Chromatographic analyses of fumarolic gases, collected in sampling bottles containing an alkaline solution, have been carried out using a thermal conductivity detector and a flame ionization detector, after catalytic conversion of CO and CH₄. The latter method enables the concentration of carbon monoxide to be measured with sufficient accuracy for use in a CO-CO₂-H₂-H₂O geothermometer. Application of this geothermometer to fumaroles in the crater of Solfatara in the Campi Flegrei, Italy, indicates that they are fed from a steam reservoir at 250±15 °C and at 10^–36±2atm of oxygen. On the other hand, the CH₄-CO₂-H₂-H₂O geothermobarometer seems to re-equilibrate at superficial temperatures and cannot be used for infering thermodynamic conditions at depth. Regular sampling of these fumaroles together with a geothermometric interpretation of the gas analyses provides a means of monitoring, with comparative accuracy, the chemical and thermal evolution of the hydrothermal reservoir below the Solfatara crater. Such monitoring would probably detect an increase in temperature at depth and the injection of magmatic gas into the reservoir.     

Βedrock instability of underground storage systems in the Czech Republic,Central Europe

Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH₄), the geological disposal of CO₂, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m^?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure.     

过坝下泄水流中温室气体排放速率的数值模拟

当水流通过泄洪建筑物下泄时,水体中所溶解的温室气体(二氧化碳(CO2)、甲烷(CH4)等)会因为所受压力的瞬间改变而导致溶解度降低,从而造成气液之间传质的发生及水中温室气体的排放.然而,目前对于泄流条件下水中温室气体排放的研究还较为缺乏.鉴于原型观测与模型试验的局限性,本文建立了大坝泄流条件下温室气体排放速率的数学模型...     

城市景观湖泊不同时间尺度CH4通量特征及影响因素分析——以南京市莫愁湖为例

城市景观湖泊对温室气体的收支发挥着重要作用。本文以南京市莫愁湖为研究对象,采用静态箱—温室气体分析仪法实时监测湖泊水—气界面CH₄通量,分析湖泊主要温室气体CH₄在日尺度和季节尺度上因冒泡和扩散排放方式不同对其通量的影响,探究影响湖泊CH₄通量的因素。结果表明:(1)在日尺度上,四季24 h内CH₄均呈排放状态,受白天冒泡影响,四季CH₄总通量均存在白天高于夜间的日变化特征。(2)在季节尺度上,莫愁湖CH₄排放通量呈现显著的时空异质性,受冒泡通量的影响夏季CH₄通量明显高于春、秋、冬三季;B区的CH₄总通量(6.04 nmol/(m²·s))显著高于A区(3.82 nmol/(m²·s)),水体的营养化程度和离岸距离是空间变化的主要影响因素。A、B两区CH₄排放夏季以冒泡排放为主,春、秋、冬以扩散排放为主。(3)在日尺度上,CH₄     

Evidence that piezometers vent gas from peat soils and implications for pore‐water pressure and hydraulic conductivity measurements

Entrapped gas bubbles in peat can alter the buoyancy, storativity, void ratio and expansion/contraction properties of the peat. Moreover, when gas bubbles block water‐conducting pores they can significantly reduce saturated hydraulic conductivity and create zones of over‐pressuring, perhaps leading to an alteration in the magnitude and direction of groundwater flow and solute transport. Some previous researches have demonstrated that these zones of over‐pressuring are not observed by the measurements of pore‐water pressures using open‐pipe piezometers in peat; rather, they are only observed with pressure transducers sealed in the peat. In has been hypothesized that open‐pipe piezometers vent entrapped CH₄ to the atmosphere and thereby do not permit the natural development of zones of entrapped gas. Here we present findings of the study to investigate whether piezometers vent subsurface CH₄ to the atmosphere and whether the presence of piezometers alters the subsurface concentration of dissolved CH₄. We measured the flux of methane venting from the piezometers and also determined changes in pore‐water CH₄ concentration at a rich fen in southern Ontario and a poor fen in southern Quebec, in the summer of 2004. Seasonally averaged CH₄ flux from piezometers was 1450 and 37·8‐mg CH₄ m^?2 d^?1 at the southern Ontario site and Quebec site, respectively. The flux at the Ontario site was two orders of magnitude greater than the diffusive flux at the site. CH₄ pore‐water concentrations were significantly lower in open piezometers than in water taken from sealed samplers at both the Ontario and Quebec sites. The flux of CH₄ from piezometers decreased throughout the season suggesting that CH₄ venting through the piezometer exceeded the rate of methanogenesis in the peat. Consequently we conclude that piezometers may alter the gas dynamics of some peatlands. We suggest that less‐invasive techniques (e.g. buried pressure transducers, tracer experiments) are needed for the accurate measurement of pore‐water pressures and hydraulic conductivity in peatlands with a large entrapped gas component. Furthermore, we argue that caution must be made in interpreting results from previous peatland hydrology studies that use these traditional methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Methan- und Sauerstoffhaushalt im mesotrophen Lungernsee

Prealpine Lake Lungern shows in spite of low primary production rates (120 g C/m². year) and full winter overturns a complete oxygen depletion in the deepest hypolimnion (65–70 m below surface) towards the end of summer stagnation. Periodical examinations of O₂- and CH₄-concentrations, CH₄-oxidation rates and temperature in the water column during 1975/76 enabled an O₂-balance of Lake Lungern. The direct measurement of the CH₄-flux at the sediment-water-interface and of the CH₄-concentrations in sediment cores as well as the determination of the age of methane bubbles lead to the conclusion, that the hypolimnic oxygen depletion is partly due to the oxidation of fossile methane penetrating the lake from below.      

Dasuopu ice core record of atmospheric methane over the past 2000 years

The concentrations of CH₄ in the atmosphere over the past 2000 years have been deduced by extracting and analyzing the air in bubbles embedded in the Dasuopu ice core, Qing-hai-Tibetan Plateau. Upon analyzing 57 ice core samples we found that the concentration of CH₄ 200 years ago and earlier was 0.85 μ mol· mol^-1 or about 40% of present atmospheric CH₄ levels over Qinghai-Tibetan Plateau. A rapid and significant increase of atmospheric CH₄ started about 200–250 a ago. For a given age before 19th century, the Dasuopu CH₄ concentrations were about 15%-20% higher than those in Antarctic and Greenland references. It was also found that the Dasuopu CH₄ concentrations changed more frequently, and its fluctuations could reflect the temperature change sensitively.     

Groundwater impact on methane emissions from flooded paddy fields

High methane (CH₄) fluxes emitted from paddy fields strongly contribute to the accumulation of greenhouse gases into the atmosphere, compromising the eco-compatibility of one of the most important world foods. A strong link exists between infiltration rates of irrigation water and CH₄ emissions. Since depth to the groundwater table affects infiltration rates, a relevant groundwater impact is expected on CH₄ emissions from paddy fields. In this work, a theoretical approach is adopted to investigate the aquifer effect on CH₄ dynamics in paddies. Infiltration rates are strongly affected by the development of different connection states between aquifer and irrigation ponded water. A strong reduction in infiltration rates results from a water table near to the soil surface, when the system is hydraulically connected. When the groundwater level increases, the infiltration rate reduction due to the switch from disconnected to connected state promotes a relevant increase of CH₄ emissions. This is due to a strong reduction of dissolved organic carbon (DOC) percolation, which leads to higher DOC availability for microbial CH₄ production and, consequently, higher CH₄ emissions. Our simulations show that CH₄ fluxes can be reduced by up to 24% when groundwater level is decreased and the aquifer is disconnected from ponding water. In paddies with shallow aquifers, lowering the water table with a drainage system could thus represent a promising CH₄ mitigation option.     

Climate tipping-point potential and paradoxical production of methane in a changing ocean

The global warming potential of methane (CH₄) is about 30 times stronger than that of carbon dioxide (CO₂) over a century timescale. Methane emission is hypothesized to have contributed to global climate change events and mass extinctions during Earth’s history. Therefore, the study of CH₄ production processes is critically important to the understanding of global climate change. It has been a dogma that biogenic CH₄ detectable in the oceans originates exclusively from the anaerobic metabolic activity of methanogenic archaea in hypoxic and anoxic environments, despite reports that many oxic surface and near-surface waters of the world’s oceans are CH₄-supersaturated, thereby rendering net sea-to-air emissions of CH₄. The phenomenon of CH₄ production in oxic marine waters is referred to as the “ocean methane paradox”. Although still not totally resolved, recent studies have generated several hypotheses regarding the sources of CH₄ production in oxic seawater. This review will summarize our current understanding of the importance of CH₄ in the global climate and analyze the biological processes and their underpinning mechanisms that lead to the production of CH₄ in oxic seawater environments. We will also tentatively explore the relationships of these microbial metabolic processes with global changes in climate and environment.     

水力调控对湖泊甲烷扩散通量的影响

外源引水等水力调控措施常用于湖泊水环境综合整治中,作为人类施加到湖泊显著的外界活动,其对湖泊甲烷(CH4)扩散通量的影响鲜有报道.贡湖湾作为"引江济太"工程长江来水进入太湖的第一站,其CH4通量变化是对水力调控的最好响应.基于2011年11月至2013年8月逐月的野外观测表明,贡湖湾平均CH4扩散排放量为0.073 m...     

Bacterial biogas production in coastal systems affected by freshwater inputs

The concentrations of two greenhouse gases, nitrous oxide (N₂O) and methane (CH₄), and the bacterial processes involved in their production (nitrification and denitrification for N₂O, and methanogenesis for CH₄), were determined in surface waters of two coastal areas under the influence of freshwater inputs, on one part in the Gulf of Lions and the Rhone River plume, in northwestern Mediterranean Sea, and on the other part in the inner Thermaikos Gulf, in Aegean Sea, eastern Mediterranean Sea. High concentrations of dissolved CH₄ and N₂O were recorded in the surface waters of Gulf of Lions and Gulf of Thermaikos, up to 1300 nM for CH₄, and 40 nM for N₂O. No direct relationship could be found between the concentration and production of the biogases, as they may also be produced in deep water or bottom sediment in shallow areas, or derived from anthropogenic activity or ship contamination in polluted areas. Irrespective of the origin of CH₄ and N₂O, the presence of extremely high concentrations of these two gases in superficial seawater implies that they can easily escape to the atmosphere; consequently, these nearshore waters enriched in greenhouse gases may play an important role in the increase in atmospheric concentration of both CH₄ and N₂O.     

Relation between hydrogen emission and seismic activities

Measurements of chemical composition of bubbles from a mineral spring at Yuya Spa situated close to the Median Tectonic Line, the longest active fault in Japan, showed that the periods of increased H₂ emission coincided with occurrences of the Ohno earthquake swarm nearby. Four cases of the coincidence without exception were observed in the last three years. The fluctuation of H₂ concentration ranges between <0.5 and 200 ppm, whereas other gases such as He, Ar, N₂, and CH₄ do not fluctuate much. The H₂ concentration is correlated with the energy released by the seismic activity. This field evidence, together with the results of laboratory experiments conducted bySugisaki et al. (1983), leads to the conclusion that H₂ observed at the mineral spring was produced by the reaction between groundwater and rock fractured in the seismic activities. The observation that H₂ in the mineral spring tends to appear prior to an earthquake suggests that microcracks may occur in rocks prior to earthquakes. The precursory emission of H₂ may be useful for earthquake prediction.     

No evidence for thermogenic methane release in coal from the Karoo-Ferrar large igneous province

The Early Jurassic Toarcian oceanic anoxic event (T-OAE) and concurrent negative carbon-isotope (δ¹³C) excursion have recently been attributed to either the release of methane (CH₄) clathrates or thermogenic CH₄ gas associated with the Karoo-Ferrar large igneous province (LIP) into coals and organic-rich shales. ¹²C-enriched thermogenic CH₄ production associated with the Karoo-Ferrar would result in residual material being ¹²C-depleted nearer the intrusions. In this study, geochemical analyses (carbon isotopes, volatile matter (VM), vitrinite reflectance (R_o)) are reported for two coal transects associated with dykes intruding the No. 4L coal in the Highveld Coalfield, Karoo Basin, South Africa. VM decreases from over 35% to around 15% in one transect, and the second transect shows a less pronounced decrease (from > 25% to ~ 16%). Accompanying the decrease in VM content is an increase in R_o from background levels of around 0.7% to over 4% adjacent to the dyke; used as a palaeo-geothermometer, R_o values indicate background temperatures of ~ 100 °C increasing to > 300 °C close to the contact. Despite changes in VM and R_o, there are no significant changes in δ¹³C, certainly not of the magnitude that would be expected associated with large-scale thermogenic CH₄ generation. These and other Gondwanan coals have low vitrinite and liptinite contents (components more prone to CH₄ generation), in part explaining the modest decreases in VM adjacent to the dykes. This, combined with the relatively narrow metamorphic aureole surrounding the intrusions and the likelihood that at least some of the volatiles generated by the intrusion were trapped as coalbed CH₄ or condensed as pyrolytic carbon, suggests only limited CH₄ release. In addition, based on original estimates of moisture contents in these coals and the depth at time of intrusion (1,000–2,000 m) the dykes would have lost most of their energy heating and evaporating water, thus having very little remaining energy to generate thermogenic CH₄.     

The solar occultation for ice experiment

The Solar Occultation For Ice Experiment (SOFIE) was launched onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite on 25 April 2007, and began science observations on 14 May 2007. SOFIE conducts solar occultation measurements in 16 spectral bands that are used to retrieve vertical profiles of temperature, O₃, H₂O, CO₂, CH₄, NO, and polar mesospheric cloud (PMC) extinction at wavelengths from 0.330 to 5.006 μm. SOFIE performs 15 sunset measurements at latitudes from 65° to 85°S and 15 sunrise measurements from 65° to 85°N each day. This work describes the SOFIE instrument, measurement approach, and retrieval results for the northern summer of 2007.     

Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)

This paper focuses on the chemical and isotopic features of dissolved gases (CH₄ and CO₂) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH₄ and CO₂. The δ¹³C-CH₄ and δD-CH₄ values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH₄ is mainly produced by microbial activity. The δ¹³C-CO₂ values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO₂ contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO₂ source feeding the regional thermal and cold CO₂-rich fluid emissions. In contrast, the relatively low δ¹³C-CO₂ values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO₂. Chemical and isotopic compositions of dissolved CO₂ and CH₄ at different depths are mainly depending on (1) CO₂ inputs from external sources (hydrothermal and/or anthropogenic); (2) CO₂–CH₄ isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO₂ and CH₄ concentrations. In the hypolimnion, where the δ¹³C-CO₂ values progressively increase with depth and the δ¹³C-CH₄ values show an opposite trend, biogenic CO₂ production from CH₄ using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ¹³C-CO₂ values, and measured δ¹³C_TDIC values are not consistent, indicating that CO₂ and the main carbon-bearing ion species (HCO₃ ^?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO₂ and CH₄. This study demonstrates that the vertical patterns of the CO₂/CH₄ ratio and of δ¹³C-CO₂ and δ¹³C-CH₄ are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO₂ input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.     

Methane consumption in Cariaco Trench waters and sediments

Detailed measurements of CH₄ in the water column and sediments of the Cariaco Trench show that CH₄ is non-conservative in both environments. Concentration differences between the sediments and adjacent overlying water suggest that the sediments are the source of the water column CH₄. Co-metabolism of CH₄ by sulfate reducers appears to be the CH₄ sink in anoxic environments.