Methane Release Rates Research Articles

Calibration of a fugitive emission rate measurement of an area source

A major challenge to measuring fugitive emission rates from large area sources, such as landfills or tailings ponds, has been the establishment of the accuracy of such methods, or of a particular measurement. When such measurements are carried out, they are invariably associated with a relatively high degree of uncertainty. The Airborne Matter Mapping (AMM) method is a new method of measuring fugitive emission rates that can be applied to large area sources. The method was applied to the measurement of methane emissions from a landfill to assess the potential accuracy of the method, and the measurement process was calibrated to increase confidence in the measured value. First, a measured rate of methane from a gas cylinder was released from near the center of the landfill and the AMM method was applied to measure the methane flow rate across a measurement surface. Then, the AMM method was performed a second time along the same measurement surface without the intentional release of methane. The difference of the flow rates across the measurement surface were then compared with the measured rate of methane released from the gas cylinder. The relatively small difference of –5.7% between the flow rates, relative to the methane release rate from the gas cylinder, provides confidence in the accuracy of this AMM method measurement. An adjustment to the AMM method analysis was made such that the difference between the flow rates was negligible, which resulted in a calibrated measurement of the methane emission rate from the landfill of 0.87 g/sec. Implications: To properly manage fugitive emissions to the atmosphere, accurate measurement of fugitive emission rates is necessary. The Airborne Matter Mapping (AMM) method has the potential to provide accurate measurements of fugitive emission rates from large area sources, such as landfills, tailings ponds, and mines. The measurements can be calibrated against the metered release of a standard. This calibration can provide confidence in the accuracy of an AMM method measurement of the fugitive emission rate from a source.

Sediment Trapping by Dams Creates Methane Emission Hot Spots

Inland waters transport and transform substantial amounts of carbon and account for ∼18% of global methane emissions. Large reservoirs with higher areal methane release rates than natural waters contribute significantly to freshwater emissions. However, there are millions of small dams worldwide that receive and trap high loads of organic carbon and can therefore potentially emit significant amounts of methane to the atmosphere. We evaluated the effect of damming on methane emissions in a central European impounded river. Direct comparison of riverine and reservoir reaches, where sedimentation in the latter is increased due to trapping by dams, revealed that the reservoir reaches are the major source of methane emissions (∼0.23 mmol CH4 m(-2) d(-1) vs ∼19.7 mmol CH4 m(-2) d(-1), respectively) and that areal emission rates far exceed previous estimates for temperate reservoirs or rivers. We show that sediment accumulation correlates with methane production and subsequent ebullitive release rates and may therefore be an excellent proxy for estimating methane emissions from small reservoirs. Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7%.

Recent Development in IR Sensor Technology for Monitoring Subsea Methane Discharge

AbstractRecently developed methane sensors, based on infrared (IR) absorption technology, were successfully utilized for subsea methane release measurements. Long-term investigation of methane emissions (fluid flux determination) from natural methane seeps in the Hikurangi Margin offshore New Zealand were performed by using seafloor lander technology. Small centimeter-sized seep areas could be sampled at the seafloor by video-guided lander deployment. In situ sensor measurements of dissolved methane in seawater could be correlated with methane concentrations measured in discrete water samples after lander recovery. High backscatter flares determined by lander-based Acoustic Doppler Current Profiler (ADCP) measurement indicate bubble release from the seafloor. Highest methane concentrations determined by the IR sensor coincided with periods of high ADCP backscatter signals. The high fluid release cannot be correlated with tidal changes only. However, this correlation is possible with variability in spatial bubble release, sudden outbursts, and tidal changes in more quiescent seepage phases.A recently developed IR sensor (2,000 m depth-rated) with a detection limit for methane of about 1 ppm showed good linearity in the tested concentration range and an acceptable equilibration time of 10 min. The sensor was successfully operated offshore Santa Barbara by a small work-class ROV at a natural methane seep (Farrar Seep). High background methane concentration of 50 nmol L−1 was observed in the coastal water, which increases up to 560 nmol L−1 in dissolved methane plumes south of the seepage area. ROV- and lander-based sensor deployments have proven the applicability of IR sensor technology for the determination of subsea methane release rates and plume distribution. The wide concentration range, low detection limit, and its robust detection unit enable this technology for both subsea leak detection and oceanographic trace gas investigations.

Stable carbon isotopes of invertebrate remains: do they reveal past methane release from lakes?

Lakes are a source of methane, an important greenhouse gas in the atmosphere. In order to understand increasing methane emissions in the present, it is important to study the variations of methane release during past periods of climate change. However, records of methane release from lakes over time scales longer than a few years are extremely rare. In this thesis a method is explored to reconstruct past methane availability in lakes based on the stable carbon isotope composition (delta 13C) of aquatic invertebrate remains. Methane-derived 13C-depleted carbon can be an alternative carbon source to plant-derived material for invertebrates in the sediment and water column of lakes, that can lead to markedly depleted delta 13C values in invertebrate tissues. Using culturing experiments, it was demonstrated that methane-derived carbon is incorporated into chironomid head capsules. Also, it was shown that chemical pre-treatments that are commonly used for sediment processing do not have a noticeable effect on delta 13C values of chironomid remains and that a minimum of 20 microgram chitinous material is required for reproducible delta 13C measurements. In study lakes in Sweden and Siberia, delta 13C values of chitinous remains of several invertebrate taxa in surface sediments were negatively correlated with diffusive methane fluxes. Strong and significant correlations are observed between diffusive methane fluxes and delta 13C of Chironomini and Daphnia remains. Similar correlations were also observed within two Swedish lakes, in which surface sediment cores were obtained along depth transects. Delta 13C values of Chironomini and Daphnia were lower in sections of the lake basin in which the sediments had higher methane release rates. This suggests that delta 13C in remains of several invertebrates, especially Chironomini and Daphnia can be indicative of methane availability in lakes. In contrast, Orthocladiinae and Ephemeroptera, always had relatively high delta 13C values, indicating a plant-derived carbon source. In a sediment record from a Siberian thermokarst lake, delta 13C values of the remains of Chironomini and Daphnia showed relatively large negative delta 13C shifts in warm periods (AD 850-1150 and since AD 1970) compared with delta 13C values of Orthocladiinae remains and bulk sediment. Based on the observed correlations between methane fluxes and delta 13C values of Chironomini and Daphnia in surface sediment samples, this suggests that more methane-derived carbon was available in warm periods compared with colder periods. The research in this thesis demonstrates the potential to use taxon-specific stable carbon isotopes analysis of invertebrate remains for qualitative reconstructions of methane availability in lakes. This new method can lead to a better understanding of lake methane emissions in relation to climate change

Methane and possible gas hydrates in the Disko Bugt region, central West Greenland

Current climate models predict an annual temperature increase in the Arctic between 4° and 6°C by the end of the 21st century with widespread impact on the Arctic environment. Warming will lead to thawing of the widespread, permanently frozen, high-latitude peat-lands and to degradation of marine gas hydrates, both of which may increase the rate of methane release to the atmosphere. This will influence global climate as methane is a potent greenhouse gas with a large global warming potential. Marine gas hydrates are found worldwide on continental margins and frequently occur in the Arctic. Interpretation of seismic profiles has also indicated their presence in the Disko Bugt region in western Greenland.

Kinetics of methane clathrate formation and dissociation under Mars relevant conditions

Spectral observations have detected methane within the martian atmosphere (Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. [2004]. Science 306, 1758–1761; Mumma, M.J. et al. [2009]. Science 323, 1041–1045), however, the origin of the methane has not been determined. Methane clathrate (also referred to as methane hydrate) has been suggested as a potential subsurface reservoir, storing and releasing biologic and/or abiogenic methane. In this study, rates of methane hydrate formation and dissociation were measured experimentally at 234–264K and 1.4–4.7MPa to test the clathrate reservoir hypothesis. Initial formation rates range from 4.3×10−6 to 8.1×10−5molm−2s−1. Results show decreasing rates of formation over time in individual experiments, indicating initial rapid clathration, followed by diffusion-limited transport of methane into the ice through the previously formed hydrate. These experiments indicate increased pressure results in increased formation rates, likely the result of higher concentration gradients, enhancing the methane diffusion flux into the solid phase. Experiments conducted at elevated temperatures produced faster initial rates of formation, resulting from increased kinetic energy of methane molecules and/or thickening of the Quasi-Liquid Layer. Based on this temperature dependence, the activation energy for methane hydrate formation from ice was determined to be 35.9kJ/mol. Hydrate dissociation experiments initiated by depressurization or warming at conditions between 222K and 265K and 0.1–2.0MPa were conducted following each formation experiment, yielding methane hydrate dissociation rates from 3.01×10−6 to 9.92×10−5molm−2s−1. While both hydrate dissociation and formation showed decreasing instantaneous rates over the course of each experiment, the transition between the initial rate of dissociation and the interpreted diffusion-limited period of continued dissociation was more abrupt than that observed in formation experiments, supporting an ice shielding effect. The initial concentration of methane in the solid phase had a significant effect on hydrate dissociation rates. Higher methane concentrations in the solid phase produce faster initial rates, likely due to increased concentration gradients, thus increasing the diffusion component of dissociation. Increased temperatures also produced faster dissociation rates, yielding an activation energy for dissociation of 32.7kJ/mol. The rates determined within this study suggest that small near-surface methane hydrate reservoirs are a feasible source for recent methane plumes detected on Mars. Rates of methane release from gas hydrates also indicate that gas hydrate dissociation may have played a role in forming ancient chaos terrain and associated outflow channels.

Release of methane from aerobic soil: An indication of a novel chemical natural process?

Methane (CH 4) formation under aerobic conditions has been intensely debated, especially since the discovery of CH 4 generation by both dried plant material and living plants. In this study we test the hypothesis that non-microbial CH 4 formation also occurs in soils. All lyophilised soil samples investigated under aerobic conditions released CH 4 at temperatures ranging from 30 to 70 °C exceeding that allowing normal enzymatic activity to proceed. No emissions were observed for single mineral soil components such as quartz sand, clay mineral and iron oxide. Methane release rates from the soils investigated were found to increase both with increasing temperature and higher organic carbon content. Addition of water to dried soils increased CH 4 release rates up to 8-fold those observed with the dried material. Our results suggest the existence of a chemical process in soils that produces CH 4 under aerobic conditions, a finding which has not been hitherto reported.

Quantification of ebullitive and diffusive methane release to atmosphere from a water storage

Accurately quantifying total freshwater storage methane release to atmosphere requires the spatial–temporal measurement of both diffusive and ebullitive emissions. Existing floating chamber techniques provide localised assessment of methane flux, however, significant errors can arise when weighting and extrapolation to the entire storage, particularly when ebullition is significant. An improved technique has been developed that compliments traditional chamber based experiments to quantify the storage-scale release of methane gas to atmosphere through ebullition using the measurements from an Optical Methane Detector (OMD) and a robotic boat. This provides a conservative estimate of the methane emission rate from ebullition along with the bubble volume distribution. It also georeferences the area of ebullition activity across entire storages at short temporal scales. An assessment on Little Nerang Dam in Queensland, Australia, demonstrated whole storage methane release significantly differed spatially and throughout the day. Total methane emission estimates showed a potential 32-fold variation in whole-of-dam rates depending on the measurement and extrapolation method and time of day used. The combined chamber and OMD technique showed that 1.8–7.0% of the surface area of Little Nerang Dam is accounting for up to 97% of total methane release to atmosphere throughout the day. Additionally, over 95% of detectable ebullition occurred in depths less than 12 m during the day and 6 m at night. This difference in spatial and temporal methane release rate distribution highlights the need to monitor significant regions of, if not the entire, water storage in order to provide an accurate estimate of ebullition rates and their contribution to annual methane emissions.

Fugitive coal mine methane emissions at five mining areas in China

Abstract Large quantities (about 28 billion m3) of methane are released to the atmosphere every year from coal-mining activities around the world. This methane represents not only a significant greenhouse gas that is contributing to global temperature change, but is also a wasted energy resource. China, the largest coal producer in the world, is responsible for over 50% of the total global release of methane-containing ventilation air from coal mines. A mine site investigation methodology was developed for collecting reliable methane emission data from coal mines. Five main coal-mining areas in China were studied and specific data were collected from two mines in each of the five mining groups. Information such as coal and methane reserves, ventilation air released, methane concentration and methane release rates were collected. Future development plans were evaluated and used to estimate potential future emissions. It was determined that most of the methane generated in the five mining areas is currently released to the atmosphere.

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ∼200 m2 area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ∼450 moles of CH4 per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO2, which should act to dissolve carbonates. The average δ13C of the carbonates was −29.2 ± 2.8‰ VPDB, compared to a range of −1.0 to +7.8‰ for CO2 in the seep gas, indicating that CO2 from the seep gas is quantitatively not as important as 13C-depleted bicarbonate derived from methane oxidation. Methane, with a δ13C of approximately −43‰, is oxidized and the resulting inorganic carbon precipitates as high-magnesium calcite and other carbonate minerals. This finding is supported by 13C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ13C ranged from −84 to −25‰). The inconsistency in δ13C between the carbonates and the seeping CO2 was resolved by discovering pockets of gas trapped near the base of the sediment column with δ13C-CO2 values ranging from −26.9 to −11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment–bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.

Recovery of Methane from Hydrate Formed in a Variable Volume Bed of Silica Sand Particles

The decomposition of methane hydrate crystals formed in sediment at 1.0, 4.0, and 7.0 °C was studied in a new apparatus designed to accommodate three different size volume beds of silica sand particles. The sand particles are microporous with a 0.9 nm pore diameter and have an average diameter equal to 329 μm. The hydrate was formed in the interstitial spaces between sand particles, and the hydrate crystal decomposition was driven by heating (thermal stimulation). The amount of methane released from the dissociating hydrate in each experiment (methane recovery curve) was determined, and it was shown that the release of gas proceeds in two stages in terms of rate. The rate of methane release (recovery) per mole of water depends on the bed size for the first stage of hydrate dissociation. The second stage rate does not depend on the bed size. This work suggests that the comparison of simulated data to experimental results from laboratory synthesized hydrate and possibly from natural samples should be done w...

Methane release from millipedes and other soil invertebrates in Central Europe

The potential for methane production was investigated in 47 species of soil invertebrates. No detectable methane production was found in slugs, earthworms, potworms, oribatid mites, woodlices, springtails, centipedes, ants and soil diptera larvae. However, significant methane production was found in several temperate millipedes including some species from the order Julida ( Leptoiulus trilobatus, Megaphyllum projectum, Megaphyllum unilineatum, Unciger transsilvanicus, Unciger foetidus, Leptoiulus proximus and Julus scandinavius). On the other hand, methane production was not confirmed in Cylindroiulus boleti which belongs to the same family. Members of the other orders (Glomerida and Polydesmida) did not release methane with the exception of one questionable recorded release in Polydesmus complanatus (Polydesmida, Polydesmidae). Methane producing species of millipedes showed significantly lower weight-specific rates of methane release than the cockroach Periplaneta americana and termite Prorhinotermes simplex. Methane release from millipedes was temperature-dependent; for the temperature range 5–25 °C, a Q 10 between 1.55 and 2.17 was calculated and the relationship between methane release and temperature was described by an exponential curve. Our results suggest that although overall methane fluxes from soil invertebrates under study cannot substantially influence a methane budget in most ecosystems, methane production is significant at least in some millipedes and therefore can impact mesoenvironments and microenvironments inhabited by these invertebrates. This work also confirms that methane production is not only supported by tropic soil invertebrates, but also by temperate species.

Biogeochemistry of inter-reef sediments on the northern and central Great Barrier Reef

The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m−2 year−1 (inshore reefs) to 2.1–4.9 kg m−2 year−1 (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged from 1.7 to 11.4 mol C m−2 year−1 and total nitrogen mineralization ranged from 77 to 438 mmol N m−2 year−1, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m−2 day−1) and methane release (range 0–12.8 μmol CH4 m−2 day−1) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O2 consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification ranged from 150 to 1,725 μmol NH4 m−2 day−1, sufficient to support high rates of denitrification (range 30–2,235 μmol N2 m−2 day−1). N2O release was not detected and rates of NH4+ and NO2− + NO3− efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef.

Global Methane Emissions from Terrestrial Plants

Recent measurements suggest that the terrestrial plant community may be an important source of methane with global contributions between 62 and 236 Tg CH4 y(-1). If true, terrestrial plants could rival wetlands as being the largest global source of methane forcing us to rethink the methane budget. While further measurements are needed to confirm the methane release rates from this source and their dependencies, in this work we use the preliminary measurements to assess the potential impact of the methane release from this source globally. Using novel techniques we extrapolate the initially reported chamber measurements to the global scale and calculate the global methane emissions from the terrestrial plant community to be in the range 20 to 69 Tg CH4 y(-1). The spread in emissions is largely due to the sensitivity of the global flux to the prescribed temperature dependence of the plant emission rate, which is largely unknown. The spread of calculated emissions is in good agreement with the upper limit imposed on the source during the late pre-industrial period, which we estimate to range from 25 to 54 Tg CH4 y(-1) during the years 0 to 1700 A.D. using the published atmospheric delta13CH4 record. In addition, if we assume that plant emissions have been constant at the mean value of 45 Tg CH4 y(-1), we find that the methane release from wildfires and biomass burning during the pre-industrial span 0-1000 A.D. must be near 12 Tg CH4 y(-1), which would be in better agreement with previous estimates of the pyrogenic source during this time than a methane budget missing the plant source. We conclude that methane release from the terrestrial plant community as presently understood does not require major innovations to the global methane budget.

Methane desorption from a coal-bed

We study the desorption of methane from a coal-bed. A model taking into account both methane diffusion in coal – blocks and its filtration through the system of open pores and cracks is developed. Methane pressure in the coal-bed is found for an arbitrary instant of time. Dependency of the rate of methane release upon the block size, open and closed porosity, viscosity, solubility, bed pressure and temperature is established. We derive the effective coefficient of diffusion of methane in blocks containing closed pores filled with gaseous methane. It is shown that at a hindered diffusion methane is distinctly divided into the “quick” and the “slow” one.

Supplementation of a tropical grass diet with forage legumes and Sapindus saponaria fruits: effects on in vitro ruminal nitrogen turnover and methanogenesis

In two in vitro experiments with the RUSITEC-apparatus, Brachiaria dictyoneura was tested alone and with legumes at dietary proportions of 1/3, 2/3, or 3/3 of Arachis pintoi (Expt 1) and 1/3 of Arachis pintoi, Cratylia argentea, or Calliandra calothyrsus (Expt 2). In Expt 2, all diets were evaluated with and without 80 mg/g diet of Sapindus saponaria fruits. In Expt 1, the stepwise replacement of the grass by A. pintoi curvi-linearly increased rumen fluid concentrations of ammonia, volatile fatty acids, bacteria, and protozoa. Methane release rates were 1.7, 7.3, 8.8, and 9.0�mmol/day. With increasing legume proportion, more organic matter and protein were degraded, the latter being only partially recovered as ammonia. In Expt 2, 1/3 of A. pintoi basically had the same effects as in Expt 1. Cratylia argentea was less effective in modifying the fermentation pattern. In association with a higher nutrient degradation and rumen ammonia concentration, C. argentea and A. pintoi increased methane release to about 3- and 4-fold levels. Calliandra calothyrsus reduced nutrient degradation and methane release per gram of organic matter degraded. Tannins, predominant in C. calothyrsus, might have affected methanogenesis. Sapindus saponaria reduced methanogenesis by 11% on average in grass-alone and legume-supplemented diets.

Methane production and release from two New England peatlands.

The rate of methane production and release to the atmosphere was determined for two New England peat bogs. Methane production rates from peat sediments, which were measured down to depths of 150 cm, ranged from 1 to 15 micromoles per liter per hour. The highest rates of methane production occurred at depths of 60-100 cm. Methane release from these same peats was quantified from various habitats on the bog using gas collection chambers. The chambers enclose a two-liter volume and cover an area of 0.02 m2. Methane accumulation in the chambers was measured for periods of up to 18 days. Methane release was related to pH and habitat zone. The lowest rates of methane release were from those portions of the bogs that had pH values below 5.0. Peak methane release occurred during or immediately after ice melt in both wetlands with release rates as high as 34 mmoles/m2/d. The overall estimate of yearly release of methane from these bog systems is 2,900 and 14,900 moles per year for Arcadia and Hawley Bogs respectively. Both of these bogs have pH environments close to the lowest limit for methanogenesis, and small differences in pH values can have a large impact on both the rate of methane production and the rate of methane release to the atmosphere.

Methane release from stands of water horsetail (Equisetum fluviatile) in a boreal lake

Summary1. Annual and diel variations in methane (CH4) release in stands of Equisetum fluviatile were measured from June to November in Lake Pääjärvi, southern Finland, where E. fluviatile is the dominant emergent macrophyte. An estimate of total annual release of CH4 from stands of E. fluviatile in this lake was also made. Diel variation was measured twice (June and August), whereas measurements for annual variation were performed monthly. The hypothesis that a relationship exists between the productivity of stands and CH4 release was also tested, whereupon net ecosystem exchange (NEE) of CO2 as well as standing stock of E. fluviatile were determined, in addition to simultaneous recordings of air temperature and solar radiation.2. Seasonal variations in CH4 release were pronounced, with the highest release rate of 813 mg m–2 day–1 measured in July and the lowest 6.5 mg m–2 day–1 in November, when the shoreline was already frozen.3. Methane release rates were strongly correlated with mean air temperature in the measuring chambers and with total solar radiation. There was no significant correlation between the instantaneous radiation and CH4 release rates.4. The seasonal patterns of CH4 release and NEE of CO2 resembled each other, except in July when NEE suddenly dropped. The decrease in NEE coincided with the highest CH4 release rate measured and the highest temperature during the measuring period, i.e. 32 °C outside and 37 °C inside the chamber. Excluding this date, daily CH4 release was strongly correlated with NEE (r2 = 0.971).5. No diel changes in CH4 release rates were detected. In June and August the maximum release rates were 11.4 and 16.8 mg CH4 m–2 h–1, respectively.6. The standing stock of E. fluviatile at different times of the growing season was not correlated with CH4 efflux; the CH4 release rates could be related neither to the number of shoots, i.e. sufficient conduits for gas transport were always present, nor to the shoot biomass in the measuring chambers.7. For an estimate of the annual release, the monthly values measured at noon were integrated over the entire growing season; this resulted in 43.7 g CH4 m–2 for the annual emission. The total annual emission of CH4 from the area covered with E. fluviatile in Lake Pääjärvi was calculated to be ≈ 5000 kg.8. Significant amounts of CH4 are released from stands of E. fluviatile in boreal lakes. The CH4 release rate follows a seasonal pattern but there is no diel pattern. Methane release rate can be related to temperature, solar radiation and NEE of CO2, but not to the standing stock of E. fluviatile or the number of shoots.

Use of a Three-Stage Laboratory Model to Determine the Effects of Temperature on Individual Trophic Groups of Methanogenic Associations Isolated from Anoxic Landfill

A three-stage continuous culture model system was used to determine the effects of temperature on methanogenic associations enriched and isolated from landfill sites. This system allowed spatial segregation of the trophic groups of the associations without disruption of the integrity of the associations. Three intermediates of anoxic catabolism in landfill sites were selected as the carbon sources for the study : cellobiose, butyrate and valerate. No evidence of thermophilic methanogenic activity was found in any of the systems. However, some thermophilic sulphate-reducing activity was detected. No inhibition of the cellobiose-degrading bacteria was evident over the range 20-55°C. The optimum temperature range for methanogenesis was generally 30-35°C, although there were apparently two methanogenic populations, one of which maintained methane release rates over the range 20-35°C.

Methane release rate and methanogenic bacterial populations in lake sediments

Methane release rates from the sediment in the lake were estimated by a batch culture. The methane release rates were decreased from 6.1 ± 0.7 mgCH 4-m −2-h −1 at top 5 cm depth to 2.6 mgCH 4-m −2-h −1 at 20–30 cm depth of sediments. Overall methane release rate from sediments was 19.9 mgCH 4-m −2-h −1. The maximum specific acetate- and H 2-utilization rates, ν m, were 5.2 × 10 −5 to 7.96 × 10 −6 and 0.9 × 10 −5 to 1.0 × 10 −4 gCOD-gVSS −1-h −1 for the sediments collected in the depths of sediments, respectively. The half-velocity constant, K s, were from 21 to 65.5 and 27 to 194 mgCOD-1 −1 for acetate-and H 2-utilizing methanogens in the depths of sediments, respectively. The acetate-utilizing methanogens were enumerated by the most probable number (MPN) technique, and showed the number of acetate-utilizing methanogens increases as the ν m increases. The populational distributions were 5.27 × 10 8 to 2.8 × 10 8, and 1.2 × 10 8 MPN-gVSS −1 at the sediments of top 20 and 20–30 cm, respectively. The specific methane production rates of sediments ranged from 1.2 × 10 −11 to 3.3 × 10 −11 mgCH 4-MPN −1-h −1 (average = 2.1 × 10 −11 mgCH 4-MPN −1-h −1) and are reasonably close to values reported in anaerobic treatment reactors and marine sediments. The sediment of top 20 cm had high microbial activity compared with the deeper section at 20–30 cm depth. In addition, the number of H 2-utilizing methanogens was smaller than that of acetate-utilizing methanogens in the sediments.