Showing papers on "Methane published in 1994"

Field and laboratory studies of methane oxidation in an anoxic marine sediment: Evidence for a methanogen-sulfate reducer consortium

Abstract: Field and laboratory studies of anoxic sediments from Cape Lookout Bight, North Carolina, suggest that anaerobic methane oxidation is mediated by a consortium of methanogenic and sulfate-reducing bacteria. A seasonal survey of methane oxidation and CO2 reduction rates indicates that methane production was confined to sulfate-depleted sediments at all times of year, while methane oxidation occurred in two modes. In the summer, methane oxidation was confined to sulfate-depleted sediments and occurred at rates lower than those of CO2 reduction. In the winter, net methane oxidation occurred in an interval at the base of the sulfate-containing zone. Sediment incubation experiments suggest both methanogens and sulfate reducers were responsible for the observed methane oxidation. In one incubation experiment both modes of oxidation were partially inhibited by 2-bromoethanesulfonic acid (a specific inhibitor of methanogens). This evidence, along with the apparent confinement of methane oxidation to sulfate-depleted sediments in the summer, indicates that methanogenic bacteria are involved in methane oxidation. In a second incubation experiment, net methane oxidation was induced by adding sulfate to homogenized methanogenic sediments, suggesting that sulfate reducers also play a role in the process. We hypothesize that methanogens oxidize methane and produce hydrogen via a reversal of CO2 reduction. The hydrogen is efficiently removed and maintained at low concentrations by sulfate reducers. Pore water H2 concentrations in the sediment incubation experiments (while net methane oxidation was occurring) were low enough that methanogenic bacteria could derive sufficient energy for growth from the oxidation of methane. The methanogen-sulfate reducer consortium is consistent not only with the results of this study, but may also be a feasible mechanism for previously documented anaerobic methane oxidation in both freshwater and marine environments.

The growth rate and distribution of atmospheric methane

Abstract: Methane was measured in air samples collected approximately weekly from a globally distributed network of sites from 1983 to 1992. Sites range in latitude from 90°S to 82°N. All samples were analyzed by gas chromatography, with flame ionization detection at the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado, and the measurements were referenced against a single calibration scale. The estimated precision of the measurements is ±0.2%. Samples which had clear sampling or analytical errors, or which appeared to be contaminated by local CH4 sources, were identified and excluded from the data analysis. The data reveal a strong north-south gradient in methane with an annual mean difference of about 140 ppb between the northernmost and southernmost sampling sites. Methane time series from the high southern latitude sites have a relatively simple seasonal cycle with a minimum during late summer-early fall, almost certainly dominated by the seasonality in its photochemical destruction. Typical seasonal cycle amplitudes there are about 30 ppb. Seasonal cycles at sites in the northern hemisphere are complex when compared to sites in the southern hemisphere due to the interaction among CH4 sources and sinks, and atmospheric transport. Seasonal cycle amplitudes in the high north are about twice those observed in the high southern hemisphere. Annual mean methane mixing ratios were ∼1% lower at 3397 m than at sea level on the island of Hawaii. Trends were determined at each site in the network and globally. The average increase in the globally averaged methane mixing ratio over the period of these measurements is (11.1±0.2) ppb yr−1. Globally, the growth rate for methane decreased from approximately 13.5 ppb yr−1 in 1983 to about 9.3 ppb yr−1 in 1991. The growth rate of methane in the northern hemisphere during 1992 was near zero. Various possibilities for the long-term, slow decrease in the methane growth rate over the last decade and the rapid change in growth rate in the northern hemisphere in 1992 are given. The most likely explanation is a change in a methane source influenced directly by human activities, such as fossil fuel production.

Methane hydrate stability in seawater

Abstract: Experimental data are presented for methane hydrate stability conditions in seawater (S ≈ 33.5‰). For the pressure range of 2.75–10.0 MPa, at any given pressure, the dissociation temperature of mcthane hydrate is depressed by approximately −1.1°C relative to the pure methane-pure water system. These experimental results are consistent with previously reported thermodynamic predictions and experimental results obtained with artificial seawater. Collectively these results provide a minimum constraint concerning depth ranges over which methane hydrate is stable in the oceanic environment.

Thermogenic and Secondary Biogenic Gases, San Juan Basin, Colorado and New Mexico--Implications for Coalbed Gas Producibility

Abstract: The San Juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 Gcf (FOOTNOTE *) (124 billion m3), resources of approximately 50 Tcf (14 trillion m3), and proved reserves of over 6 Tcf (170 billion m3) Coalbed gas wells with the highest production (initial potential greater than 10 Mcf/day or 028 million m3/day) occur in the overpressured, north-central part of the basin Hydrologic analysis indicates that overpressure in the Fruitland Formation is artesian in origin and represents repressuring that developed during the middle Pliocene Highly permeable, laterally continuous coal beds override abandoned shoreline Pictured Cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic, regionally interconnected aquifer system Coal rank and basin hydrodynamics control the composition of Fruitland coalbed gases, which varies significantly across the basin Chemically dry gases in the north-central part of the basin coincide with meteoric recharge and regional overpressure The consistency of methane ^dgr13C values across the basin, the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters, and biodegraded n-alkane distributions of some coal extracts indicate that coalbed gases in the north-central basin are a mixture of thermogenic (25-50%), secondary biogenic (15-30%), and migrated thermogenic (12-60%) gases Migrated, conventionally and hydrodynamically trapped gases, in-situ generated secondary biogenic gases, and solution gases result in gas content that plot on or above the coal sorption isotherm Bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components, n-alkanes, and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification, uplift, erosion, and cooling These gases may be limited to basin margins, where shallow depths and structural deformation result in higher permeability, or may extend more than 35 mi (56 km) basinward from the recharge zone The presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity Basin hydrogeology, reservoir heterogeneity, location of permeability barriers (no-flow boundaries), and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic-rich rocks

Methane steam reforming in asymmetric Pd- and Pd-Ag/porous SS membrane reactors

Abstract: This work is devoted to applying electrolessly deposited Pd- and Pd-Ag/porous stainless steel composite membranes in methane steam reforming The methane conversion is significantly enhanced by the partial removal of hydrogen from the reaction location as a result of diffusion through the Pd-based membranes For example, at a total pressure of 136 kPa, a temperature of 500°C, a molar steam-to-methane ratio of 3, and in the presence of a commercial Ni/Al2O3 catalyst together with continuous pumping on the permeation side, a methane conversion twice as high as that in a non-membrane reactor was reached by using a Pd/SS membrane These effects were examined under a variety of experimental conditions A computer model of the membrane reactor was also developed to predict the effects of membrane separation on methane conversion

Methane in the Baltic and North Seas and a Reassessment of the Marine Emissions of Methane

Abstract: During three measurement campaigns on the Baltic and North Seas, atmospheric and dissolved methane was determined with an automated gas chromatographic system. Area-weighted mean saturation values in the sea surface waters were 113 ± 5% and 395 ± 82% (Baltic Sea, February and July 1992) and 126 ± 8% (south central North Sea, September 1992). On the bases of our data and a compilation of literature data the global oceanic emissions of methane were reassessed by introducing a concept of regional gas transfer coefficients. Our estimates computed with two different air-sea exchange models lie in the range of 11-18 Tg CH4 yr-1. Despite the fact that shelf areas and estuaries only represent a small part of the world's ocean they contribute about 75% to the global oceanic emissions. We applied a simple, coupled, three-layer model to numerically simulate the time dependent variation of the oceanic flux to the atmosphere. The model calculations indicate that even with increasing tropospheric methane concentration, the ocean will remain a source of atmospheric methane.

Gas hydrate that breaches the sea floor on the continental slope of the Gulf of Mexico

Abstract: We report observations that concern formation and dissociation of gas hydrate near the sea floor at depths of ∼540 m in the northern Gulf of Mexico. In August 1992, three lobes of gas hydrate were partly exposed beneath a thin layer of sediment. By May 1993, the most prominent lobe had evidently broken free and floated away, leaving a patch of disturbed sediment and exposed hydrate. The underside of the gas hydrate was about 0.2 °C warmer than ambient sea water and had trapped a large volume of oil and free gas. An in situ monitoring device, deployed on a nearby bed of mussels, recorded sustained releases of gas during a 44 day monitoring period. Gas venting coincided with a temporary rise in water temperature of 1 °C, which is consistent with thermally induced dissociation of hydrate composed mainly of methane and water. We conclude that the effects of accumulating buoyant force and fluctuating water temperature cause shallow gas hydrate alternately to check and release gas venting.

Ecosystem and physiological controls over methane production in northern wetlands

Abstract: Peat chemistry appears to exert primary control over methane production rates in the Canadian Northern Wetlands Study (NOWES) area. We determined laboratory methane production rate potentials in anaerobic slurries of samples collected from a transect of sites through the NOWES study area. We related methane production rates to indicators of resistance to microbial decay (peat C: N and lignin: N ratios) and experimentally manipulated substrate availability for methanogenesis using ethanol (EtOH) and plant litter. We also determined responses of methane production to pH and temperature. Methane production potentials declined along the gradient of sites from high rates in the coastal fens to low rates in the interior bogs and were generally highest in surface layers. Strong relationships between CH4 production potentials and peat chemistry suggested that methanogenesis was limited by fermentation rates. Methane production at ambient pH responded strongly to substrate additions in the circumneutral fens with narrow lignin: N and C: N ratios (delta CH4/delta EtOH = 0.9-2.3 mg/g) and weakly in the acidic bogs with wide C: N and lignin: N ratios (delta CH4/delta EtOH = -0.04-0.02 mg/g). Observed Q(sub 10) values ranged from 1.7 to 4.7 and generally increased with increasing substrate availability, suggesting that fermentation rates were limiting. Titration experiments generally demonstrated inhibition of methanogenesis by low pH. Our results suggest that the low rates of methane emission observed in interior bogs during NOWES likely resulted from pH and substrate quality limitation of the fermentation step in methane production and thus reflect intrinsically low methane production potentials. Low methane emission rates observed during NOWES will likely be observed in other northern wetland regions with similar vegetation chemistry.

Diffusion coefficients for hydrogen sulfide, carbon dioxide, and nitrous oxide in water over the temperature range 293--368 K

Abstract: Acid gases such as H[sub 2]S and CO[sub 2] are generally removed from natural gas, biogas, synthetic natural gas, and other process gas streams by means of absorption into aqueous alkanolamine solutions. A key parameter needed to model this diffusion with chemical reaction process in the liquid phase is the diffusion coefficient. A wetted-sphere absorption apparatus was used to measure the liquid-phase diffusion coefficients for hydrogen sulfide, carbon dioxide, and nitrous oxide over the temperature range 293--368 K. The experimental results obtained in this work are compared with values in the literature and with predictions from the Wilke-Chang equation. The data presented here extend the temperature range of reported diffusivities for these gases in water.

Mechanistic analysis of ammonium inhibition of atmospheric methane consumption in forest soils.

Abstract: Methane consumption by forest soil was studied in situ and in vitro with respect to responses to nitrogen additions at atmospheric and elevated methane concentrations. Methane concentrations in intact soil decreased continuously from atmospheric levels at the surface to 0.5 ppm at a depth of 14 cm. The consumption rate of atmospheric methane in soils, however, was highest in the 4- to 8-cm depth interval (2.9 nmol per g of dry soil per day), with much lower activities below and above this zone. In contrast, extractable ammonium and nitrate concentrations were highest in the surface layer (0 to 2 cm; 22 and 1.6 μmol per g of dry soil, respectively), as was potential ammonium-oxidizing activity (19 nmol per g of dry soil per day). The difference in zonation between ammonium oxidation and methane consumption suggested that ammonia-oxidizing bacteria did not contribute significantly to atmospheric methane consumption. Exogenous ammonium inhibited methane consumption in situ and in vitro, but the pattern of inhibition did not conform to expectations based on simple competition between ammonia and methane for methane monooxygenase. The extent of ammonium inhibition increased with increasing methane concentration. Inhibition by a single ammonium addition remained constant over a period of 39 days. In addition, nitrite, the end product of methanotrophic ammonia oxidation, was a more effective inhibitor of methane consumption than ammonium. Factors that stimulated ammonium oxidation in soil, e.g., elevated methane concentrations and the availability of cosubstrates such as formate, methanol, or β-hydroxybutyrate, enhanced ammonium inhibition of methane oxidation, probably as a result of enhanced nitrite production.

Sources of Combustion Irreversibility

Abstract: Approximately 1/3 of the useful energy of the fuel is destroyed during the combustion process used in electrical power generation. This study is an attempt to clarify and categorize the reasons for the exergy destruction taking place in combustion processes. The entropy production is separated into three subprocesses: (1) combined diffusion/fuel oxidation, (2) “internal thermal energy exchange” (heat transfer), and (3) the product constituent mixing process. Four plausible process paths are proposed and analyzed. The analyses are performed for two fuels: hydrogen and methane. The results disclose that the majority (about 3/4) of the exergy destruction occurs during the internal thermal energy exchange. The fuel oxidation, by itself, is relatively efficient, having an exergetic efficiency of typically 94% to 97%.

Direct catalytic conversion of methane to acetic acid in an aqueous medium

Abstract: ALTHOUGH methane is the most-abundant of alkanes, hazards of handling and distribution prevent known methane reserves1,2 from being fully exploited. Moreover, it is the least reactive alkane, so whereas selective conversion to more useful chemical products would be of great value, it is difficult to achieve. A useful target molecule for methane conversion is acetic acid, but existing approaches to this conversion on an industrial scale involve many steps under extreme reaction conditions3–5. Previous reports of the direct catalytic conversion of methane to acetic acid have involved peroxydisulphate as the oxidant6,7, but any such process that could be adapted to large-scale applications would have to use O2 as the oxidant. Here we describe such a process, which uses rhodium trichloride as the catalyst, proceeds in an aqueous medium at a temperature of around 100 °C, and gives high yields of acetic acid. This reaction provides a potentially useful means to convert methane directly to an industrially useful organic compound and greatly expands the scope of catalytic functionalization of alkanes.

Production and transport of methane in oceanic particulate organic matter

Abstract: METHANE is an important component of the global carbon cycle1 and a potent greenhouse gas2,3. Surface ocean waters are typically supersaturated with dissolved methane relative to atmospheric equilibrium, presumably as a result of in situ microbial methane production4–8. Because methanogenic bacteria are strict anaerobes9and surface ocean waters are highly oxygenated, the observation of methane supersaturation has been termed the 'oceanic methane paradox'10. Although methanogenic bacteria have been isolated from oceanic particulate matter, faecal pellets and zooplankton11–14, no data are available on in situ rates of methane formation in these microenvironments. During a series of experiments in the North Pacific ocean, we have identified a previously unrecognized component of the oceanic methane cycle. We find that methane is associated with sinking particles, presumably as a dissolved constituent of the interstitial fluids of particulate biogenic materials, which exchanges with the water column as particles sink. This phenomenon provides a mechanism for the active transport in the water column of an otherwise passive, dissolved species. The particle-to-seawater methane flux that we measure is sufficient to replace all of the methane present in the upper water column in about 50 days and to produce the characteristic methane supersaturations in less than a month. We suggest that particulate production and transport may also be relevant to the redistribution and cycling of other bioreactive compounds in the marine environment.

A three-year study of controls on methane emissions from two Michigan peatlands

Abstract: We investigate temporal changes in methane emissions over a three-year period from two peatlands in Michigan. Mean daily fluxes ranged from 0.6–68.4 mg CH4 m−2d−1 in plant communities dominated by Chamaedaphne calyculata, an eficaceous shrub, to 11.5–209 mg CH4 m−2d−1 in areas dominated by plants with aerenchymatous tissues, such as Carex oligosperma and Scheuchzeria palustris. Correlations between methane flux and water table position were significant at all sites for one annual cycle when water table fluctuations ranged from 15 cm above to 50 cm below the peat surface. Correlations were not significant during the second and third annual periods with smaller water table fluctuations. Methane flux was strongly correlated with peat temperatures at −5 to −40 cm (r s = 0.82 to 0.98) for all three years at sites with flora acting as conduits for methane transport. At shrub sites, the correlations between methane flux and peat temperature were weak to not significant during the first two years, but were strong in the third year. Low rates of methane consumption (−0.2 to −1.5 mg CH4 m−2 d−1 ) were observed at shrub sites when the water table was below −20 cm, while sites with plants capable of methane transport always had positive net fluxes of methane. The methane oxidizing potential at both types of sites was confirmed by peat core experiments. The results of this study indicate that methane emissions occur at rates that cannot be explained by diffusion alone; plant communities play a significant role in altering methane flux from peatland ecosystems by directly transporting methane from anaerobic peat to the atmosphere.

Potential distribution of methane hydrates in the world's oceans

Abstract: Estimates of the magnitudes and spatial distribution of potential oceanic methane hydrate reservoirs have been made from pressure-temperature phase relations and a plausible range of thermal gradients, sediment porosities, and pore fillings taken from published sources, based on two major theories of gas hydrate formation (1) in situ bacterial production and (2) pore fluid expulsion models The implications of these two models on eventual atmospheric methane release, due to global warming, are briefly examined The calculated range of methane volumes in oceanic gas hydrates is 264 to 1391 x 10{sup 15} m{sup 3}, with the most likely value on the lower end of this range The results for the bacterial model show a preferential distribution of hydrates at mid- to high latitudes, with an equatorial enhancement in the case of the fluid migration model The latter model also generates a deeper and thicker hydrate stability zone at most latitudes than does the former Preliminary results suggest that the hydrate distribution predicted by the fluid migration model may be more consistent with observations However, this preliminary finding is based on a very limited sample size, and there are high uncertainties in the assumptions The volume of methane hydrate within the uppermostmore » 1 m of the hydrate stability zone and within 1{degrees}-2{degrees}C of the equilibrium curve, assuming in situ bacterial generation, is 093-632 x 10{sup 12} m{sup 3}, or 00035-0012% of the maximal estimated hydrate reservoir Nevertheless this volume, if released uniformly over the next 100 years, is comparable to current CH{sub 4} release rates for several important CH{sub 4} sources Corresponding CH{sub 4} volumes calculated using the fluid migration model are nearly 2 orders of magnitude lower 52 refs, 2 figs, 5 tabs« less

Effect of increasing atmospheric methane concentration on ammonium inhibition of soil methane consumption

Abstract: SOILS currently consume about 30–40 Tg methane per year1,2, which is comparable to the net annual increase in atmospheric methane concentration from 1980 to 19903. Most soils consume methane2,4–9, but the extent varies with soil water content, land use and ammonium inputs5,10–13. Ammonium concentrations in many soils have increased in recent years as a result of land-use changes and increases in ammonium concentration in precipitation14,15. Ammonium strongly inhibits soil methane consumption, but the mechanism is uncertain. Even if enhanced ammonium concentrations are subsequently reduced, inhibition can still persist for months to years12,13. Here we show, from field and laboratory experiments, that the extent of ammonium inhibition increases with increasing methane concentration. We propose that nitrite formation from methanotrophic ammonium oxidation accounts for much of the observed inhibition, and that the persistence of inhibition with reduced ammonium concentrations is due to the limited capacity of methanotrophs to grow or recover in present concentrations of atmospheric methane. We suggest that past increases in atmospheric methane concentration may have increased the inhibitory effect of ammonium, thereby decreasing soil methane uptake capacity, and that this mechanism could also provide a positive feedback on future atmospheric methane concentrations.

Methane emission by bubbling from Gatun Lake, Panama

Abstract: We studied methane emission by bubbling from Gatun Lake, Panama, at water depths of less than 1 m to about 10 m. Gas bubbles were collected in floating traps deployed during 12- to 60-hour observation periods. Comparison of floating traps and floating chambers showed that about 98% of methane emission occurred by bubbling and only 2% occurred by diffusion. Average methane concentration of bubbles at our sites varied from 67% to 77%. Methane emission by bubbling occurred episodically, with greatest rates primarily between the hours of 0800 and 1400 LT. Events appear to be triggered by wind. The flux of methane associated with bubbling was strongly anticorrelated with water depth. Seasonal changes in water depth caused seasonal variation of methane emission. Bubble methane fluxes through the lake surface into the atmosphere measured during 24-hour intervals were least (10-200 mg/m2/d) at deeper sites (greater than 7 m) and greatest (300-2000 mg/m2/d) at shallow sites (less than 2 m).

Investigation of Pt/Al2O3 and Pd/Al2O3 catalysts for the combustion of methane at low concentrations

Abstract: Pt/Al 2 O 3 and Pd/Al 2 O 3 catalysts have been prepared from chlorine-free precursors and investigated for the combustion of methane under lean, stoichiometric, and rich conditions using dilute mixtures. It has been found that under lean conditions, and at low conversions under stoichiometric or rich conditions, Pd/Al 2 O 3 is a more effective catalyst. However, at higher conversions with stoichiometric or rich mixtures Pt/Al 2 O 3 is a more active catalyst. This change over between Pd/Al 2 O 3 and Pt/Al 2 O 3 is associated with a ‘light-off’ effect observed with Pt/Al 2 O 3 catalysts. Various possible explanations for these effects are discussed. With the Pt/Al 2 O 3 catalysts there is no evidence of a particle size effect, which is in contrast to reports in the literature that the methane combustion reaction is structure sensitive. Reasons for these variations, including the possible inhibition of activity by chlorine used in many catalyst preparations, are discussed. It is concluded that platinum can be a more effective catalyst than palladium for methane combustion under real conditions and that, in consequence, platinum may play an important role in multimetallic catalysts for emission control for natural gas vehicles.

Laminar flame speeds and extinction strain rates of mixtures of carbon monoxide with hydrogen, methane, and air

Abstract: The effect of hydrogen and methane addition on the propagation and extinction of atmospheric CO/airflames was investigated experimentally and numerically. Experiments were conducted by using the counterflow, twin-flame technique and laser-Doppler velocimetry for the determination of laminar flame speeds and extinction strain rates. The simulation was conducted by using the one-dimensional flame code, and by solving the conservation equations of mass, momentum, energy, and species along the stagnation stream-line of the counterflow. In both cases, detailed description of the chemistry and transport was used. Results indicate that the addition of small amounts of hydrogen and methane to CO flames increases the laminar flame speeds and extinction strain rates by accelerating the main CO oxidation reaction. The sensitivity of the mass burning rate to this reaction is particularly high when trace amounts of hydrogen and methane are added. For large amounts of additives, the chemistry shifts toward that of the additive, and the advantages of the CO kinetic simplicity are lost. The experimental data were closely predicted by the numerical calculations for both propagation and extinction, indicating that existing CO, hydrogen, and methane kinetics can be used with confidence for similar studies. Detailed analysis of the flame structure revealed that, when CO and methane are both supplied as reactants, the CO oxidation follows that of methane, and that, for methane-rich mixtures, the supplied CO remains unreacted until the intermediate CO has been completely formed.

Selective catalytic reduction of nitric oxide with ethane and methane on some metal exchanged ZSM-5 zeolites

Abstract: The selective reduction of nitric oxide by methane or ethane, in the presence and in the absence of a large excess of oxygen, has been investigated on Cu/ZSM-5, Co/ZSM-5, Rh/ZSM-5 and Pt/ZSM-5 catalysts over a wide range of temperatures. It has been found that the maximum nitric oxide conversion is higher with ethane than with methane and the temperature of this maximum is lower with ethane. In the absence of oxygen the order of activity is Rh/ZSM-5>Pt/ZSM-5>Co/ZSM-5 > Cu/ZSM-5 with the Cu/ZSM-5 being essentially inactive, while in the presence of oxygen the order is: Rh/ZSM-5>Co/ZSM-5>Cu/ZSM-5 > Pt/ZSM-5 when ethane is used as reductant and: Rh/ZSM-5>Co/ZSM-5 > Cu/ZSM-5>Pt/ZSM-5 when methane is used. The effect of the oxygen content has been investigated for the Co/ZSM-5 catalyst. It has been found that with a small quantity of oxygen the catalytic activity decreases markedly; with higher oxygen content the activity of the catalyst rises again. It appears that two different reaction schemes may be operative, one in the absence of oxygen the other in the presence of oxygen. It is concluded that neither carbonaceous deposits, nor nitrogen dioxide formation in the gas phase are important in the reaction mechanism on metal-containing zeolites. It is proposed that the reaction is essentially a redox process in which decomposition of nitric oxide occurs on reduced metallic or metal ion sites (the relative activity of each of these depending on the choice of metal), leading to the formation of gaseous nitrogen and adsorbed oxygen, followed by the removal of the adsorbed oxygen by the hydrocarbon, thus recreating the active centres.

Methane and carbon dioxide fluxes from poorly drained adjacent cultivated and forest sites.

Abstract: Methane and carbon dioxide fluxes at the soil surface were measured from April to November 1992 in Ottawa, on adjacent cultivated (corn) and forest (temperate woodland) sites using closed chambers (10 chambers per site). The objectives were to quantify the spatial and temporal variability of gas exchange rates, and to determine the effects of soil temperature and moisture on the fluxes. On the forest soil, rates of CO2 emissions and CH4 uptake ranged from 2.27 to 14.82 g m−2 d−1 and from 0.04 to 1.10 mg m−2 d−1, respectively. On the cultivated soil, the measured CO2 fluxes varied from 0.27 to 7.07 g m−2 d−1 while methane uptake ranged from 0 to 0.13 mg m−2 d−1. There was a positive correlation between soil surface CO2 fluxes and soil temperature for the forest (R2 = 0.74, s(ŷ) = 1.77 g m−2 d−1) and the cultivated (R2 = 0.48, s(ŷ) = 1.10 g m−2 d−1) sites. Temperature had little effect on methane uptake by the forest soil suggesting that gas diffusion was rate limiting. This was further substantiated by the...

Ammonium and nitrite inhibition of methane oxidation by Methylobacter albus BG8 and Methylosinus trichosporium OB3b at low methane concentrations

Abstract: Methane oxidation by pure cultures of the methanotrophs Methylobacter albus BG8 and Methylosinus trichosporium OB3b was inhibited by ammonium choride and sodium nitrite relative to that in cultures assayed in either nitrate-containing or nitrate-free medium. M. albus was generally more sensitive to ammonium and nitrite than M. trichosporium. Both species produced nitrite from ammonium; the concentrations of nitrite produced increased with increasing methane concentrations in the culture headspaces. Inhibition of methane oxidation by nitrite was inversely proportional to headspace methane concentrations, with only minimal effects observed at concentrations of>500 ppm in the presence of 250 μM nitrite. Inhibition increased with increasing ammonium at methane concentrations of 100 ppm. In the presence of 500 μM ammonium, inhibition increased initially with increasing methane concentrations from 1.7 to 100 ppm; the extent of inhibition decreased with methane concentrations of > 100 ppm. The results of this study provide new insights that explain some of the previously observed interactions among ammonium, nitrite, methane, and methane oxidation in soils and aquatic systems.