Ebullition Of Methane Research Articles

Diverse sediment microbiota shape methane emission temperature sensitivity in Arctic lakes

Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH4) from sediments. Ebullitive CH4 flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH4 flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH4 emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH4 emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH4-cycling microorganisms and syntrophs, were predictive of porewater CH4 concentrations. Results suggest that deeper lake regions, which currently emit less CH4 than shallower edges, could add substantially to CH4 emissions in a warmer Arctic and that CH4 emission predictions may be improved by accounting for spatial variations in sediment microbiota.

Quantifying bubbling emission (ebullition) of methane from a rice paddy using high-time-resolution concentration data obtained during a closed-chamber measurement

Quantifying bubbling emission (ebullition) of methane from a rice paddy using high-time-resolution concentration data obtained during a closed-chamber measurement

Methane emission through ebullition from an estuarine mudflat: 2. Field observations and modeling of occurrence probability

AbstractEbullition can transport methane (CH4) at a much faster rate than other pathways, albeit over limited time and area, in wetland soils and sediments. However, field observations present large uncertainties in ebullition occurrences and statistic models are needed to describe the function relationship between probability of ebullition occurrence and water level changes. A flow‐through chamber was designed and installed in a mudflat of an estuarine temperate marsh. Episodic increases in CH4 concentration signaling ebullition events were observed during ebbing tides (15 events over 456 ebbing tides) and occasionally during flooding tides (4 events over 455 flooding tides). Ebullition occurrence functions were defined using logistic regression as the relative initial and end water levels, as well as tidal amplitudes were found to be the key functional variables related to ebullition events. Ebullition of methane was restricted by a surface frozen layer during winter; melting of this layer during spring thaw caused increases in CH4 concentration, with ebullition fluxes similar to those associated with large fluctuations in water level around spring tides. Our findings suggest that initial and end relative water levels, in addition to tidal amplitude, partly regulate ebullition events in tidal wetlands, modulated by the lunar cycle, storage of gas bubbles at different depths and seasonal changes in the surface frozen layer. Maximum tidal strength over a few days, rather than hourly water level, may be more closely associated with the possibility of ebullition occurrence as it represents a trade‐off time scale in between hourly and lunar periods.

Methane storage and ebullition in monimolimnetic waters of polluted mine pit lake Vollert-Sued, Germany.

Reliable gas measurements from supersaturated deep waters still remain a challenge. However, good information is mandatory to investigate the limnic carbon cycle, assess the endangerment through limnic eruptions and evaluate a potential source of exploitable energy. We addressed these three points in a heavily polluted mine pit lake in Germany. We quantified the ebullition of methane from deep waters and the sediment below. Exposed to continuous percolation of gas bubbles, the deep (monimolimnetic) water had accumulated high concentrations of gas: directly measured gas pressures indicated the proximity to spontaneous ebullition. Consequently, the possibility of a limnic eruption was assessed by initiating a self-sustained flow through a vertical pipe. Despite the high gas pressures, the flow was slow and the endangerment was considered low. A sampling strategy with bags was developed to achieve a reliable measurement of gas content and gas composition in the monimolimnion. As a result, directly measured gas pressures could be confirmed and were nearly exclusively attributed to methane and nitrogen. Contrary to lakes that had shown limnic eruptions, carbon dioxide played a much subordinate role, and hence the driving force for a violent outburst of gases was missing. Nevertheless the amount of dissolved methane was remarkably high. This investigation closes with some estimates of the commercial value of the deposit and limiting conditions for a possible exploitation.

Optimal designs for the methane flux in troposphere

The understanding of methane emission and methane absorption plays a central role both in the atmosphere and on the surface of the Earth. Several important ecological processes, e.g., ebullition of methane and its natural microergodicity request better designs for observations in order to decrease variability in parameter estimation. Thus, a crucial fact, before the measurements are taken, is to give an optimal design of the sites where observations should be collected in order to stabilize the variability of estimators. In this paper we introduce a realistic parametric model of covariance and provide theoretical and numerical results on optimal designs. For parameter estimation D-optimality, while for prediction integrated mean square error and entropy criteria are used. We illustrate applicability of obtained benchmark designs for increasing/measuring the efficiency of the engineering designs for estimation of methane rate in various temperature ranges and under different correlation parameters. We show that in most situations these benchmark designs have higher efficiency.

Ebullition of methane from peatlands: Does peat act as a signal shredder?

AbstractBubbling (ebullition) of greenhouse gases, particularly methane, from peatlands has been attributed to environmental forcings, such as changes in atmospheric pressure. However, observations from peat soils suggest that ebullition and environmental forcing may not always be correlated and that interactions between bubbles and the peat structure may be the cause of such decoupling. To investigate this possibility, we used a simple computer model (Model of Ebullition and Gas storAge) to simulate methane ebullition from a model peat. We found that lower porosity peat can store methane bubbles for lengthy periods of time, effectively buffering or moderating ebullition so that it no longer reflects bubble production signals. Our results suggest that peat structure may act as a “signal shredder” and needs to be taken into account when measuring and modeling ebullition.

Microergodicity effects on ebullition of methane modelled by Mixed Poisson process with Pareto mixing variable

We model the process of exceedences of the ebullition of methane from wetlands in the sedge–grass marsh, South Bohemia, Czech Republic by a Mixed Poisson process with mixing variable that is Pareto distributed. We investigate the properties of this process and describe it as a particular case of a counting process. We define Mixed Poisson Pareto random variable, Exponential–Pareto and Erlang–Pareto distributions and investigate their properties.

A water column study of methane around gas flares located at the West Spitsbergen continental margin

In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep area. In this area, free gas formation and gas ebullition as a consequence of hydrate dissociation due to global warming are currently under debate. Recent studies revealed shallow gas accumulation and ebullition of methane into the water column at more than 250 sites in an area of 665km2. We conducted a detailed study of a subregion of this area, which covers an active gas ebullition area of 175km2 characterized by 10 gas flares reaching from the seafloor at~245m up to 50m water depth to identify the fate of the released gas due to dissolution of methane from gas bubbles and subsequent mixing, transport and microbial oxidation.The oceanographic data indicated a salinity-controlled pycnocline situated ~20m above the seafloor. A high resolution sampling program at the pycnocline at the active gas ebullition flare area revealed that the methane concentration gradient is strongly controlled by the pycnocline. While high methane concentrations of up to 524nmolL−1 were measured below the pycnocline, low methane concentrations of less than 20nmolL−1 were observed in the water column above. Variations in the δ13CCH4 values point to a 13C depleted methane source (~−60‰ VPDB) being mainly mixed with a background values of the ambient water (~−37.5‰ VPDB). A gas bubble dissolution model indicates that ~80% of the methane released from gas bubbles into the ambient water takes place below the pycnocline. This dissolved methane will be laterally transported with the current northwards and most likely microbially oxidized in between 50 and 100 days, since microbial CH4 oxidation rates of 0.78nmold−1 were measured. Above the pycnocline, methane concentrations decrease to local background concentration of ~10nmolL−1.Our results suggest that the methane dissolved from gas bubbles is efficiently trapped below the pycnocline and thus limits the methane concentration in surface water and the air–sea exchange during summer stratification. During winter the lateral stratification breaks down and fractions of the bottom water enriched in methane may be vertically mixed and thus be potentially an additional source for atmospheric methane.

Ebullition of methane from rice paddies: the importance of furthering understanding

Flooded rice fields and other wetlands (such as peatlands) are the most important source of atmospheric methane (CH4) (Rothfuss and Conrad 1998). Whalen (2005) estimated the total annual CH4 emission at approximately 600 Tg CH4 yr −1 (anthropogenic and natural sources), of which 20 % and 24 % were attributable to rice paddies and natural wetlands, respectively. Until recently, CH4 has not been comprehensively included in C inventories in wetlands because it represents a relatively small proportion of the total C budget (e.g., in peatlands less than 10 % in mass terms of the budget (Baird et al. 2009; Thompson 2008)). The implications of such exclusion can be large in terms of Global Warming Potential (GWP) (Baird et al. 2009), although there is still great uncertainty regarding the formation, size and dynamics of key components of the soil CH4 pool. Compiling a soil methane inventory requires data on free-phase CH4, and dissolved CH4; the latter is limited by the low solubility of CH4, and lack of ionic form such as those associated with CO2 dissolution. The total soil pool is generated and regulated via the balance of methanogenesis (CH4 production), methanotrophy (CH4 oxidation) and atmospheric-soil CH4 interactions (steady/episodic ebullition, diffusion, and plant-mediated transport). Ebullition has only really expanded in research terms in the last decade, and the number of cited studies, although building is limited. Ebullition is the formation and release of bubbles (predominately containing CH4, CO2 and N-related gaseous species) from inundated sub-surface soils or sediments to the water-table and, thereafter, the atmosphere. It remains unclear how bubbles are formed, what processes and conditions are required for their formation and the prerequisites for their release and transport towards the surface. It was originally assumed that the subsurface CH4 existed primarily in the dissolved form, but it has been estimated that 33–88 % of the total CH4 sub-surface store is in the gas-phase (Tokida et al. 2005b; Strack and Waddington 2008). Bubbles are thought to form when the combined partial pressures of the dissolved gases exceed the hydrostatic pressure (Chanton and Whiting 1995). The presence of these bubbles has important biogeochemical effects, including the development of localized CH4 Plant Soil (2013) 370:31–34 DOI 10.1007/s11104-013-1790-1

Organic matter mineralisation in the hypolimnion of an eutrophic Maar lake

Constraints on hypolimnetic methane production in productive lakes are of interest owing to the importance of methane emissions from lakes for the atmospheric methane burden. We studied carbon fluxes and terminal electron accepting processes in the hypolimnion of eutrophic Meerfelder Maar, Germany. Carbon fluxes from epilimnion and sediments were estimated using sediment traps, porewater analysis and incubation techniques. The contribution of various redox processes to overall dissolved inorganic carbon (DIC) production was quantified from a seasonal hypolimnetic mass balance. Carbon sedimentation rates were 22 mmol m−2 d−1 from the epilimnion and 20–34 mmol m−2 d−1 from the hypolimnion. Anaerobic respiration accounted for a DIC production of 21 mmol m−2 d−1, and was thus capable of using a substantial part of primary production. The diffusive C flux from the sediment was small in comparison, although potential respiration rates in incubation experiments reached 63 – 75 mmol m−2 d−1. Ebullition of methane occurred, but could not be quantified. Following depletion of dissolved oxygen (DO) and nitrate, iron and sulphate reduction and methanogenesis proceeded concurrently in the hypolimnion. Estimated hypolimnetic DIC production decreased in the order methanogenesis (2267 mmol m−2) > oxic respiration (880 mmol m−2) > sulphate reduction (575mmolm−2) > denitrification (159 mmol m−2) > acetogenesis (157 mmol m−2) > iron reduction (19 – 144 mmol m−2). Methane production thus dominated respiration and was not inhibited by sulphate and iron reduction. It also strongly accelerated with increased carbon sedimentation rates in September, which apparently eased limiting factors on the process. Hypolimnetic methane production is thus likely an important process in similar lakes, even in the presence of other electron acceptors, and will contribute to methane emissions during fall turnover.

The ebullition of hydrogen, carbon monoxide, methane, carbon dioxide and total gaseous mercury from the Cornwall Area of Concern

This paper reports the first ebullitive fluxes of hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and total gaseous mercury (TGM) from the Cornwall Area of Concern (CAC). Although sediments were contaminated with mercury, bubbling was a negligible source of mercury for the global atmosphere. Indeed, the average emission of TGM through ebullition was 0.04 pg m(-2) h(-1). Measurements of H2, CO, CH4 and CO2 trapped gas concentrations and fluxes were used as indicators of diagenesis processes. The CAC represented a significant regional source of CH4 since the estimated ebullitive fluxes (3.5 mg m(-2) h(-1)) were similar to the CH4 emissions measured above typical flooded freshwater wetlands. As molecular diffusion is known as the main pathway of CO2 transport from water to the atmosphere, CO2 ebullitive fluxes were weak (0.39 mg m(-2) h(-1)). Bubbling of CO (1.6 microg m(-2) h(-1)) was 10 folds less important than CO fluxes measured over flooded freshwater wetlands. Finally, H2 emissions (0.001 microg m(-2) h(-1)) were negligible since the level of this trace gas is tightly regulated by microorganisms in anaerobic environments.

Sulfide and methane evolution in the hypolimnion of a subtropical lake: a three-year study

The differential impact of microbial sulfate reduction and methanogenesis on the mineralization of particulate organic carbon (POC) in warm monomictic Lake Kinneret (LK), Israel was studied during three consecutive lake cycles. The hypolimnetic accumulation of total sulfide and dissolved methane was examined in relation to the physical forcing of the water column and the settling flux of particulate matter. With the on-set of thermal stratification in spring, both solutes increased concomitantly with the depletion of oxygen, first in the benthic boundary layer, followed by the upper hypolimnion. Methane production was restricted to the sediments as emphasized by the persistently linear concentration gradient in the hypolimnion. Sulfate reduction occurred both in the sediments and the water column as revealed by the hypolimnetic distribution of sulfide and recurring metalimnetic sulfide peaks. Annual differences in the accumulation pattern of both solutes appeared to be primarily linked to the settling flux of POC and the length of the stratified season. Relatively lower hypolimnetic concentrations of dissolved methane during the stratified season of 2000 coincided with increased ebullition of gaseous methane, likely as the result of a nearly a 2 m drop in the lake level. Overall, sulfate reduction accounted for more than 60% of the POC settling flux, a finding that differs from similar studies made in temperate lakes where methanogenesis was shown to be the primary mode of terminal carbon mineralization. Intensive organic carbon turnover at the sediment water interface and comparatively high sulfate concentrations in LK are the most likely reason.

Potential environmental control of free shallow gas in the seafloor of Eckernförde Bay, Germany

The depth of the free methane gas horizon in Eckernförde Bay, Western Baltic Sea, was monitored over 4 months in 1-h intervals with an echo sounder mounted on a tower at the seafloor. The depth to the top of the free gas varied between 50 cm and 100 cm below seafloor. Short-term fluctuations of free gas depth are related for the most part to changes of total pressure (air pressure and water level), the observation period was too short to demonstrate the effect of the annual temperature cycle. The correlation of gas depth changes and total pressure agrees well with theory which predicts a linear influence of pressure fluctuations on gas solubility. Since the methane content in the pore water of Eckernförde Bay is at the saturation limit environmental changes (pressure and temperature variations) cannot be buffered and have an instant impact on free gas presence. The implications of this observation are manifold. Geo-technically, the bearing strength of the seafloor is altered by the presence of gas bubbles. Similarly, sonar systems are influenced by the presence of gas bubbles which alter the acoustic seafloor properties. Of ecological interest is that pressure drops can trigger a sudden ebullition of the greenhouse gas methane from the seafloor into the atmosphere.

Ebullition of methane from peat with falling atmospheric pressure

Recent works on CH4 emissions from peatlands have demonstrated that ebullition can be a more important emission pathway than it has been thought. However, knowledge of its features and associated environmental factors is still very limited. In this study, we investigated the quantitative relationship between the amount of CH4 emitted via ebullition and changes in the atmospheric pressure through a laboratory experiment. During the flux measurement period, ebullition was recorded almost exclusively in air‐pressure‐declining phases. The increased volume of the gas bubbles due to reduction in atmospheric pressure and the amount of released gas bubbles revealed a strong linear relation, suggesting that in situ CH4 emissions via ebullition can be estimated using this correlation. Our results clearly showed that atmospheric pressure can be one of the most important factors to control CH4 emissions from peatlands and that ebullition can be the main transport mechanism during the pressure‐falling phase.

Release of gas bubbles from lake sediment traced by noble gas isotopes in the sediment pore water

The release of gas bubbles from lacustrine or oceanic sediments into the overlying water (ebullition) is a major mechanism for the discharge of biogenic or geogenic gases into the water body. Ebullition of methane or carbon dioxide, for instance, contributes considerably to the release of these potent greenhouse gases through the sediment/water interface. Depending on the rate of ebullition, the pore water will show a depletion in dissolved atmospheric noble gases, because the poorly soluble noble gases escape from the pore water into the gas bubbles. In this study, the depletion of dissolved noble gases in sediment pore water was analyzed for the first time to study bubble formation and ebullition in sediments. The noble gases in the pore water of the sediments of Soppensee (Switzerland) show a distinct depletion due to ebullition of biologically produced methane. This depletion is lowest in the deep sediment and increases towards the sediment surface. The noble gas isotope ratios in the pore water indicate that vertical diffusion barely affects the observed noble gas profiles. The isotope ratios further show that the methane bubbles remain long enough in the sediment to attain noble gas solubility equilibrium before escaping into the overlying water. The volume of gas released from the sediment by ebullition can therefore be reconstructed from the extent of the noble gas depletion in the pore water using a simple gas-equilibration model. The noble gas profiles in the sediment indicate that ebullition increased in Soppensee during the Holocene, and that ebullition contributed strongly to the release of methane from the sediment. Our case study thus illustrates that noble gases are sensitive proxies for the release of gas from lacustrine and marine sediments or similar aquatic environments.

A novel sediment gas sampler and a subsurface gas collector used for measurement of the ebullition of methane and carbon dioxide from a eutrophied lake

A novel sediment bubble gas sampler and a subsurface bubble gas collector were designed to measure the ebullition of gases from profundal sediments of aquatic ecosystems. The sediment gas sampler was constructed to collect bubble gas samples directly from the uppermost sediment layers for gas composition analysis. The floating subsurface gas collector, designed to trap the bubbles released naturally from sediments, permitted the measurement of both the volume and the composition of the bubble gas. Due to its low cost, light weight and rapid sampling capability, the gas collector is ideal for studies requiring many replicate collectors. These devices were used for measurement of the ebullition of methane (CH 4) and carbon dioxide (CO 2) during an open water period from hypereutrophic Lake Postilampi, situated within the midboreal zone in Finland. The bubble gas obtained from the sediment with the sediment gas sampler had higher concentrations of CH 4 and CO 2 than the bubbles trapped in the gas collectors. This indicated that the bubble gas composition changed, either naturally during the migration of the bubbles from the sediment through the water column to the gas collectors, and/or during their storage in the collectors prior to sampling. The mean CH 4 ebullition from Lake Postilampi was estimated to be in the range from 36 to 46 mg m −2 d −1, based on the bubble gas CH 4 concentrations measured from the gas collectors and sediment, respectively. The bubbles contained only 0.02–0.57% of CO 2 and thus, the ebullition had no significance in the release of CO 2 from the lake.

Ebullition of methane

Ebullition of methane

Convective gas flow in Eleocharis sphacelata R. Br.: methane transport and release from wetlands

We investigated the importance of lacunar gas transport for the release of methane from beds of Eleocharis sphacelata R. Br. in a freshwater wetland in southeastern Australia. Gases were transported in the E. sphacelata lacunar system by pressurized convective flow, which was apparently driven by humidity induced pressurization. Internal culm temperatures were 1.9–4.2° C lower than at the external culm surface, suggesting that thermal transpiration was not responsible for lacunar pressurization. Some of the culms (influx culms) provide a net gas flux from the atmosphere into the plant, whereas others (efflux culms) act as conduits for flux from the rhizosphere to the atmosphere. The mean gas influx was 1.0±0.2 (SE) ml min −1 per culm, and the mean gas efflux was 0.2±0.0 (SE) ml min −1 per culm. The difference in influx and efflux flow rates is due to unequal numbers of the two culm types, and the total gas flux through three adjacent E. sphacelata beds was estimated from this flow ratio and the total culm density. It ranged from 1.1 to 2.5 1 m −2 h −1. The methane concentration in the efflux culms was 2–3%, resulting in a total methane efflux from E. sphacelata of 22–75 ml CH 4 m −2 h −1. These rates represented 1–15 times the rate of methane release from the E. sphacelata beds by ebullition of methane in bubbles released from the sediment. Diffusive methane fluxes in the lacunar s system (< 300 μl m −2 h −1) were an insignificant mechanism of methane release compared with lacunar convective flow and ebullition fluxes from sediments. The interstitial methane concentration in sediments from E. sphacelata beds was approximately 0.6 times that of adjacent unvegetated sediment, highlighting the role of convective flow by E. sphacelata in accelerating methane release from sediments.

Seasonal variations in ebullitive flux and carbon isotopic composition of methane in a tidal freshwater estuary

Methane carbon isotopic composition ranged from −76.9 to −62.6‰ in a tidal freshwater estuary (the White Oak River, North Carolina, United States) with site specific seasonal variations ranging from 6 to 10‰. During warmer months, tidally induced bubble ebullition actively transported this methane to the atmosphere. At two sites, these seasonally varying fluxes ranged from 1.2 ± 0.3 to 1.3 ± 0.3 mol CH4 m−2yr−1 (19.2 to 20.8 g CH4m−2yr−1), with flux‐weighted average isotopic compositions at two sites of −66.3 ± 0.4 and −69.5 ± 0.6‰. The carbon isotopic composition of naturally released bubbles was shown to be indistinguishable from the sedimentary methane bubble reservoir at three sites, leading to the conclusion that isotopic fractionation did not occur during the ebullition of methane. The hypothesis was developed that ebullitive methane fluxes are depleted in 13CH4 relative to fluxes transported via molecular diffusion or through plants, as zones of 13C enriching microbial methane oxidation are bypassed.