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Terms modified by CH4 Selected AbstractsDependency of Tritium Retention in Graphite on Temperature Control of Molecular DynamicsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010A. Ito Abstract We have investigated the carbon plasma facing material and hydrogen atom interaction by the use of molecular dynamics simulation to clarify chemical erosion processes on divertor plate. The present paper is our first try at elucidation of temperature dependence by the molecular dynamics. Temperature was controlled by using Langevin thermostat method. As a result, the retention of hydrogen atom achieve steady state, and the CH4 was generated, which was not found MD simulations without a temperature control method. About 30 percent of injected hydrogen atoms are retained. CH4 yields has a peak at 600 K, which accords with experimental results. A dominant path of CH4 generation found by the present molecular dynamics simulation is as follows: a CH is detached from eroded surface and then it grows into CH4 adsorbing hydrogen atoms via CH2 and CH3. In addition, we propose the problem that the hydrogen atom retention and CH,, yields depend on the thermal relaxation time in MD simulation using temperature control methods (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emissionECOLOGY LETTERS, Issue 10 2009Lingli Liu Abstract Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO2, CH4 and N2O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO2 exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH4 emission by 97%, reduced CH4 uptake by 38% and increased N2O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO2 reduction could be largely offset (53,76%) by N stimulation of global CH4 and N2O emission from multiple ecosystems. [source] Microbial Community Dynamics of a Continuous Mesophilic Anaerobic Biogas Digester Fed with Sugar Beet SilageENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2008B. Demirel Abstract The aim of the study was to investigate the long-term fermentation of an extremely sour substrate without any addition of manure. In the future, the limitation of manure and therefore the anaerobic digestion of silage with a very low buffering capacity will be an increasing general bottleneck for energy production from renewable biomass. During the mesophilic anaerobic digestion of sugar beet silage (without top and leaves) as the sole substrate (without any addition of manure), which had an extreme low pH of around 3.3, the highest specific gas production rate (spec. GPR) of 0.72,L/g volatile solids (VS),d was achieved at a hydraulic retention time (HRT) of 25,days compared to an organic loading rate (OLR) of 3.97,g VS/L,d at a pH of around 6.80. The methane (CH4) content of the digester ranged between 58 and 67,%, with an average of 63,%. The use of a new charge of substrate (a new harvest of the same substrate) with higher phosphate content improved the performance of the biogas digester significantly. The change of the substrate charge also seemed to affect the methanogenic population dynamics positively, thus improving the reactor performance. Using a new substrate charge, a further decrease in the HRT from 25 to 15,days did not influence the digester performance and did not seem to affect the structure of the methanogenic population significantly. However, a decrease in the HRT affected the size of the methanogenic population adversely. The lower spec. GPR of 0.54,L/g,VS,d attained on day,15 of the HRT could be attributed to a lower size of methanogenic population present in the anaerobic digester during this stage of the process. Furthermore, since sugar beet silage is a relatively poor substrate, in terms of the buffering capacity and the availability of nutrients, an external supply of buffering agents and nutrients is a prerequisite for a safe and stable digester operation. [source] Activity and composition of methanotrophic bacterial communities in planted rice soil studied by flux measurements, analyses of pmoA gene and stable isotope probing of phospholipid fatty acidsENVIRONMENTAL MICROBIOLOGY, Issue 2 2008Minita Shrestha Summary Methanotrophs in the rhizosphere of rice field ecosystems attenuate the emissions of CH4 into the atmosphere and thus play an important role for the global cycle of this greenhouse gas. Therefore, we measured the activity and composition of the methanotrophic community in the rhizosphere of rice microcosms. Methane oxidation was determined by measuring the CH4 flux in the presence and absence of difluoromethane as a specific inhibitor for methane oxidation. Methane oxidation started on day 24 and reached the maximum on day 32 after transplantation. The total methanotrophic community was analysed by terminal restriction fragment length polymorphism (T-RFLP) and cloning/sequencing of the pmoA gene, which encodes a subunit of particulate methane monooxygenase. The metabolically active methanotrophic community was analysed by stable isotope probing of microbial phospholipid fatty acids (PLFA-SIP) using 13C-labelled CH4 directly added to the rhizospheric region. Rhizospheric soil and root samples were collected after exposure to 13CH4 for 8 and 18 days. Both T-RFLP/cloning and PLFA-SIP approaches showed that type I and type II methanotrophic populations changed over time with respect to activity and population size in the rhizospheric soil and on the rice roots. However, type I methanotrophs were more active than type II methanotrophs at both time points indicating they were of particular importance in the rhizosphere. PLFA-SIP showed that the active methanotrophic populations exhibit a pronounced spatial and temporal variation in rice microcosms. [source] Methanogenesis and methanogenic pathways in a peat from subarctic permafrostENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Martina Metje Summary Few studies have dealt so far with methanogenic pathways and populations in subarctic and arctic soils. We studied the effects of temperature on rates and pathways of CH4 production and on the relative abundance and structure of the archaeal community in a mildly acidic peat from a permafrost region in Siberia (67°N). We monitored the production of CH4 and CO2 over time and measured the consumption of Fe(II), ethanol and volatile fatty acids. All experiments were performed with and without specific inhibitors [2-bromoethanesulfonate (BES) for methanogenesis and CH3F for acetoclastic methanogenesis]. The optimum temperature for methanogenesis was between 26°C and 28°C [4.3 ,mol CH4 (g dry weight),1 day,1], but the activity was high even at 4°C [0.75 ,mol CH4 (g dry weight),1 day,1], constituting 17% of that at 27°C. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Acetoclastic methanogenesis accounted for about 70% of the total methanogenesis. Most 16S rRNA gene sequences clustered with Methanosarcinales, correlating with the prevalence of acetoclastic methanogenesis. In addition, sequences clustering with Methanobacteriales were recovered. Fe reduction occurred in parallel to methanogenesis. At lower and higher temperatures Fe reduction was not affected by BES. Because butyrate was consumed during methanogenesis and accumulated when methanogenesis was inhibited (BES and CH3F), it is proposed to serve as methanogenic precursor, providing acetate and H2 by syntrophic oxidation. In addition, ethanol and caproate occurred as intermediates. Because of thermodynamic constraints, homoacetogenesis could not compete with hydrogenotrophic methanogenesis. [source] Hydrogen ,leakage' during methanogenesis from methanol and methylamine: implications for anaerobic carbon degradation pathways in aquatic sedimentsENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Niko Finke Summary The effect of variations in H2 concentrations on methanogenesis from the non-competitive substrates methanol and methylamine (used by methanogens but not by sulfate reducers) was investigated in methanogenic marine sediments. Imposed variations in sulfate concentration and temperature were used to drive systematic variations in pore water H2 concentrations. Specifically, increasing sulfate concentrations and decreasing temperatures both resulted in decreasing H2 concentrations. The ratio of CO2 and CH4 produced from 14C-labelled methylamine and methanol showed a direct correlation with the H2 concentration, independent of the treatment, with lower H2 concentrations resulting in a shift towards CO2. We conclude that this correlation is driven by production of H2 by methylotrophic methanogens, followed by loss to the environment with a magnitude dependent on the extracellular H2 concentrations maintained by hydrogenotrophic methanogens (in the case of the temperature experiment) or sulfate reducers (in the case of the sulfate experiment). Under sulfate-free conditions, the loss of reducing power as H2 flux out of the cell represents a loss of energy for the methylotrophic methanogens while, in the presence of sulfate, it results in a favourable free energy yield. Thus, hydrogen leakage might conceivably be beneficial for methanogens in marine sediments dominated by sulfate reduction. In low-sulfate systems such as methanogenic marine or freshwater sediments it is clearly detrimental , an adverse consequence of possessing a hydrogenase that is subject to externally imposed control by pore water H2 concentrations. H2 leakage in methanogens may explain the apparent exclusion of acetoclastic methanogenesis in sediments dominated by sulfate reduction. [source] Localization of processes involved in methanogenic degradation of rice straw in anoxic paddy soilENVIRONMENTAL MICROBIOLOGY, Issue 8 2001Kristin Glissmann In anoxic paddy soil, rice straw is decomposed to CH4 and CO2 by a complex microbial community consisting of hydrolytic, fermenting, syntrophic and methanogenic microorganisms. Here, we investigated which of these microbial groups colonized the rice straw and which were localized in the soil. After incubation of rice straw in anoxic soil slurries for different periods, the straw pieces were removed from the soil, and both slurry and straw were studied separately. Although the potential activities of polysaccharolytic enzymes were higher in the soil slurry than in the straw incubations, the actual release of reducing sugars was higher in the straw incubations. The concentrations of fermentation products, mainly acetate and propionate, increased steadily in the straw incubations, whereas only a little CH4 was formed. In the soil slurries, on the other hand, fermentation products were low, whereas CH4 production was more pronounced. The production of CH4 or of fermentation products in the separated straw and soil incubations accounted in sum for 54,82% of the CH4 formed when straw was not removed from the soil. Syntrophic propionate degradation to acetate, CO2 and H2 was thermodynamically more favourable in the soil than in the straw fraction. These results show that hydrolysis and primary fermentation reactions were mainly localized on the straw pieces, whereas the syntrophic and methanogenic reactions were mainly localized in the soil. The percentage of bacterial relative to total microbial 16S rRNA content was higher on the straw than in the soil, whereas it was the opposite for the archaeal 16S rRNA content. It appears that rice straw is mainly colonized by hydrolytic and fermenting bacteria that release their fermentation products into the soil pore water where they are further degraded to CH4. Hence, complete methanogenic degradation of straw in rice soil seems to involve compartmentalization. [source] The Reductive Elimination of Methane from ansa -Hydrido(methyl)metallocenes of Molybdenum and Tungsten: Application of Hammond's Postulate to Two-State ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005José-Luis Carreón-Macedo Abstract The energetic profile of the methane reductive elimination from a selected number of hydrido(methyl)molybdenocene and -tungstenocene derivatives has been calculated by DFT methods. The calculations were carried out for the CH2(C5H4)2M (a -M), SiH2(C5H4)2M (a -H2Si,M), and SiMe2(C5Me4)2M (a -Me2Si,M*) ansa -metallocene systems for M = Mo, W. They include the full optimization of minima [the hydrido(methyl) starting complexes, M(H)(CH3), the intermediate methane complexes, M(CH4), and the metallocene products in the singlet and triplet configurations, (3M and 1M)], transition states (for the methyl hydride reductive elimination, M,TSins, and for the hydrogen exchange, M,TSexch), and the minimum energy crossing point (M,MECP) leading from the singlet methane complexes to the corresponding triplet metallocenes. The results are compared with those previously obtained for the simpler (C5H5)2M (Cp2M) systems (J. C. Green, J. N. Harvey, and R. Poli, J. Chem. Soc., Dalton Trans.2002, 1861). The calculated energy profiles, notably the relative energies of M,TSins and M,MECP, are in agreement with available experimental observations for the a -Me2Si,M* systems. The comparison of the energies and geometries of the rate-determining M,TSins and M,MECP structures with those of the thermodynamically relevant minima for the various systems show the applicability of Hammond's postulate to two-state reactions. However, one notable exception serves to show that the principle is only quantitatively reliable when all the potential energy surfaces for the set of analogous reactions have similar shapes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Synthesis and Reactivity of Group 4 Zwitterionic Complexes of the Type Mt+CH2AlCl3,: One-Component Stereoselective Polymerization and Oligomerization Catalysts for Olefins and AcetylenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004John J. Eisch Abstract A reinvestigation of the interaction of TiCl4 with 2 equiv. of Me3Al in toluene between ,78 °C and 25 °C over 24 h has now established that the ultimate black product obtained is an associated zwitterion of the type [Ti+,CH2,AlCl3,]n, supported by multinuclear NMR spectroscopy and mass spectrometric and gasometric analyses of the gases evolved (CH4, H2) upon its protolysis. Chemical reactions of the zwitterion have corroborated specific aspects of its proposed structure: 1) its methylene character, by its transformation of benzophenone into 1,1-diphenylethylene; 2) its divalent titanium content, by the substantial reductive dimerization of benzophenone to tetraphenylethylene, and 3) its Lewis acidic Ti center, by its catalytic isomerization of trans -stilbene oxide to 1,1-diphenylacetaldehyde. Similar individual reactions of ZrCl4 or HfCl4 with Me3Al have led to the analogous zwitterions [Zr+,CH2,AlCl3,]n and [Hf+,CH2,AlCl3,]n, respectively. These zwitterions of Ti, Zr and Hf have been proven to be capable of the cyclotrimerization and/or polymerization of acetylenes with varying facility, as evidenced by their catalytic action on 1-hexyne, phenylacetylene, di- n -butylacetylene, and diphenylacetylene. Furthermore, all three zwitterions were able to polymerize ethylene, without any added cocatalyst, with an activity following the order Zr > Ti > Hf. The Ti and Zr zwitterions effected the stereoselective polymerization of propylene to yield 50% of isotactic polymer, and all three catalysts induced the polymerization of 1-hexene to yield 85% (Zr, Hf) or 100% (Ti) of isotactic polymer. These oligomerizations and stereoselective polymerizations of acetylenes and olefins can be rationalized through a model for the active site resembling a three-membered metallacyclopropa(e)nium ion intermediate formed from the attack of the Group 4 metal zwitterion on the unsaturated hydrocarbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Comparison of greenhouse gas fluxes and nitrogen budgets from an ombotrophic bog in Scotland and a minerotrophic sedge fen in FinlandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2010J. Drewer Northern peatlands cover approximately 4% of the global land surface area. Those peatlands will be particularly vulnerable to environmental and climate change and therefore it is important to investigate their total greenhouse gas (GHG) budgets, to determine the feedback on the climate. Nitrogen (N) is known to influence the GHG budget in particular by affecting the methane (CH4) balance. At two peatland sites in Scotland and Finland GHG fluxes of carbon dioxide (CO2), methane and nitrous oxide (N2O) and nitrogen fluxes were measured as part of the European project ,NitroEurope'. The Scottish site, Auchencorth Moss, was a GHG sink of ,321, ,490 and ,321 g CO2 eq m,2 year,1 in 2006, 2007 and 2008, respectively, with CO2 as the dominating GHG. In contrast, the dominating GHG at the Finnish site, Lompolojänkkä, was CH4, resulting in the site being a net GHG source of +485 and +431 g CO2 eq m,2 year,1 in 2006 and 2007, respectively. Therefore, Auchencorth Moss had a negative global warming potential (GWP) whilst Lompolojänkkä had a positive GWP over the investigated time period. Initial results yielded a positive N budget for Lompolojänkkä of 7.1 kg N ha,1 year,1, meaning the site was gaining nitrogen, and a negative N budget for Auchencorth Moss of ,2.4 kg N ha year,1, meaning the site was losing nitrogen. [source] Methane oxidation kinetics differ in European beech and Norway spruce soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009D. M. Degelmann Summary Coniferous forest soils often consume less of the greenhouse gas methane (CH4) than deciduous forest soils. The reasons for this phenomenon have not been resolved. It might be caused by differences in the diffusive flux of CH4 through the organic layer, pH or different concentrations of potentially inhibitory compounds. Soil samples were investigated from three adjacent European beech (Fagus sylvatica) and Norway spruce (Picea abies) stands in Germany. Maximal CH4 oxidation velocities (Vmax(app)) and Michaelis Menten constants (KM(app)), retrieved from intact soil cores at constant CH4 concentrations, temperature and matric potential, were twice as great in beech as in spruce soils. Also atmospheric CH4 oxidation rates measured in homogenized soil samples displayed the same trend. Greatest atmospheric CH4 oxidation rates were detected in the Oa horizon or in the upper 5 cm of the mineral soil. In contrast to the beech soils, the Oa horizon of the spruce soils consumed no CH4. A differential effect due to divergent diffusive flux through the litter layer was not found. pH and ammonium concentration were similar in samples from both forest soil types. Ethylene accumulation in all soils was negligible under oxic conditions. These collective results suggest that the different atmospheric CH4 uptake by beech and spruce soils is caused by different CH4 oxidizing capacities of methanotrophic communities in the Oa horizon and top mineral soil. [source] Methane and nitrous oxide fluxes from a farmed Swedish HistosolEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2009Å. Kasimir Klemedtsson Summary Fluxes of the greenhouse gases methane (CH4) and nitrous oxide (N2O) from histosolic soils (which account for approximately 10% of Swedish agricultural soils) supporting grassley and barley production in Sweden were measured over 3 years using static chambers. Emissions varied both over area and time. Methane was both produced and oxidized in the soil: fluxes were small, with an average emission of 0.12 g CH4 m,2 year,1 at the grassley site and net uptake of ,0.01 g CH4 m,2 year,1 at the barley field. Methane emission was related to soil water, with more emission when wet. Nitrous oxide emissions varied, with peaks of emission after soil cultivation, ploughing and harrowing. On average, the grassley and barley field had emissions of 0.20 and 1.51 g N2O m,2 year,1, respectively. We found no correlation between N2O and soil factors, but the greatest N2O emission was associated with the driest areas, with < 60% average water-filled pore space. We suggest that the best management option to mitigate emissions is to keep the soil moderately wet with permanent grass production, which restricts N2O emissions whilst minimizing those of CH4. [source] Methane and nitrous oxide fluxes of soils in pure and mixed stands of European beech and Norway spruceEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2006W. Borken Summary Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH4) and nitrous oxide (N2O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH4 uptake rates ranged between 18 and 48 ,g C m,2 hour,1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH4 into the mineral soil. Mean N2O emission was rather small, ranging between 6 and 16 ,g N m,2 hour,1 in all stands. Forest type had a significant effect on N2O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N2O emissions were not altered by this treatment. Surprisingly, CH4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech,spruce and pure spruce forests could decrease soil CH4 uptake, while the long-term effect on N2O emissions is expected to be rather small. [source] Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlandsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2005J. B. Yavitt Summary Rates of organic carbon mineralization (to CO2 and CH4) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid-boreal Alberta, Canada, two were in low-boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH4 production varied significantly as a function of peat type, transplant site, and the type,site interaction. All four peat soils had very small rates of CH4 production (< 20 nmol g,1 day,1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH4 production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH4 production (4000 nmol g,1 day,1) correlated with large holocellulose content, a large concentration of p -hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO2 production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO2 production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH4 and CO2 in Sphagnum -derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future. [source] Carbon monoxide uptake kinetics in unamended and long-term nitrogen-amended temperate forest soilsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2006Alvarus S. K. Chan Abstract The effect of nitrogen (N) additions on the dynamics of carbon monoxide consumption in temperate forest soils is poorly understood. We measured soil CO profiles, potential rates of CO consumption and uptake kinetics in temperate hardwood and pine control plots and plots amended with 50 and 150 kg N ha,1 year,1 for more than 15 years. Soil profiles of CO concentrations were above atmospheric levels in the high-N plots of both stands, suggesting that in these forest soils the balance between consumption and production may be shifted so that either production is increased or consumption decreased. Highest rates of CO consumption were measured in the organic horizon and decreased with soil depth. In the N-amended plots, CO consumption increased in all but one soil depth of the hardwood stand, but decreased in all soil depths of the pine stand. CO enzyme affinities increased with soil depth in the control plots. However, enzyme affinities in the most active soil depths (organic and 0,5 cm mineral) decreased in response to low levels of N in both stands. In the high-N plots, affinities dramatically-increased in the hardwood stand, but decreased in the organic horizon and increased slightly in the 0,5 cm mineral soil in the pine stand. These findings indicate that long-term N addition either by fertilization or deposition may alter the size, composition and/or physiology of the community of CO consumers so that their ability to act as a sink for atmospheric CO has changed. This change could have a substantial effect on the lifetime of greenhouse gases such as CH4 and therefore the future of Earth's climate. [source] Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and BacteriaFEMS MICROBIOLOGY REVIEWS, Issue 2 2001Jan P. Amend Abstract Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe2+, H2S, S, S2O32,, S4O62,, sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe3+, CO2, CO, NO3,, NO2,, NO, N2O, SO42,, SO32,, S2O32,, and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (,Gr°) as a function of temperature to 200°C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of ,Gr° for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (,G°) at temperatures to 200°C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of ,Gr° for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25°C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H,O, H,O,N, H,O,S, H,O,N,S, H,O,Cinorganic, H,O,C, H,O,N,C, H,O,S,C, H,O,N,S,Camino acids, H,O,S,C,metals/minerals, and H,O,P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (,Gr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems. [source] Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherenceFRESHWATER BIOLOGY, Issue 3 2000George W. Kling 1. We studied the spatial and temporal patterns of change in a suite of twenty-one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty-four sites were sampled between one and five times a year from 1991 to 1997. 2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In-lake processing tended to consume alkalinity, conductivity, H+, DIC, Ca2+, Mg2+, CO2, CH4, and NO3,, and produce K+ and dissolved organic carbon (DOC). In-stream processing resulted in the opposite trends (e.g. consumption of K+ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign. 3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca2+, Mg2+, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes. 4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg2+ the average synchrony for all twenty-one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time. 5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective. [source] Aboveground plant biomass, carbon, and nitrogen dynamics before and after burning in a seminatural grassland of Miscanthus sinensis in Kumamoto, JapanGCB BIOENERGY, Issue 2 2010YO TOMA Abstract Although fire has been used for several thousand years to maintain Miscanthus sinensis grasslands in Japan, there is little information about the nutrient dynamics in these ecosystems immediately after burning. We investigated the loss of aboveground biomass; carbon (C) and nitrogen (N) dynamics; surface soil C change before and after burning; and carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes 2 h after burning in a M. sinensis grassland in Kumamoto, Japan. We calculated average C and N accumulation rates within the soil profile over the past 7300 years, which were 58.0 kg C ha,1 yr,1 and 2.60 kg N ha,1 yr,1, respectively. After burning, 98% of aboveground biomass and litter were consumed. Carbon remaining on the field, however, was 102 kg C ha,1. We found at least 43% of C was possibly lost due to decomposition. However, remaining C, which contained ash and charcoal, appeared to contribute to C accumulation in soil. There was no difference in the amount of 0,5 cm surface soil C before and after burning. The amount of remaining litter on the soil surface indicated burning appeared not to have caused a reduction in soil C nor did it negatively impact the sub-surface vegetative crown of M. sinensis. Also, nearly 50 kg N ha,1 of total aboveground biomass and litter N was lost due to burning. Compared with before the burning event, postburning CO2 and CH4 fluxes from soil appeared not to be directly affected by burning. However, it appears the short time span of measurements of N2O flux after burning sufficiently characterized the pattern of increasing N2O fluxes immediately after burning. These findings indicate burning did not cause significant reductions in soil C nor did it result in elevated CO2 and CH4 emissions from the soil relative to before the burning event. [source] Microbiology and geochemistry of Little Hot Creek, a hot spring environment in the Long Valley CalderaGEOBIOLOGY, Issue 2 2010T. J. VICK A culture-independent community census was combined with chemical and thermodynamic analyses of three springs located within the Long Valley Caldera, Little Hot Creek (LHC) 1, 3, and 4. All three springs were approximately 80 °C, circumneutral, apparently anaerobic and had similar water chemistries. 16S rRNA gene libraries constructed from DNA isolated from spring sediment revealed moderately diverse but highly novel microbial communities. Over half of the phylotypes could not be grouped into known taxonomic classes. Bacterial libraries from LHC1 and LHC3 were predominantly species within the phyla Aquificae and Thermodesulfobacteria, while those from LHC4 were dominated by candidate phyla, including OP1 and OP9. Archaeal libraries from LHC3 contained large numbers of Archaeoglobales and Desulfurococcales, while LHC1 and LHC4 were dominated by Crenarchaeota unaffiliated with known orders. The heterogeneity in microbial populations could not easily be attributed to measurable differences in water chemistry, but may be determined by availability of trace amounts of oxygen to the spring sediments. Thermodynamic modeling predicted the most favorable reactions to be sulfur and nitrate respirations, yielding 40,70 kJ mol,1 e, transferred; however, levels of oxygen at or below our detection limit could result in aerobic respirations yielding up to 100 kJ mol,1 e, transferred. Important electron donors are predicted to be H2, H2S, S0, Fe2+ and CH4, all of which yield similar energies when coupled to a given electron acceptor. The results indicate that springs associated with the Long Valley Caldera contain microbial populations that show some similarities both to springs in Yellowstone and springs in the Great Basin. [source] A thermodynamic analysis of the anaerobic oxidation of methane in marine sedimentsGEOBIOLOGY, Issue 5 2008D. E. LAROWE ABSTRACT Anaerobic oxidation of methane (AOM) in anoxic marine sediments is a significant process in the global methane cycle, yet little is known about the role of bulk composition, temperature and pressure on the overall energetics of this process. To better understand the biogeochemistry of AOM, we have calculated and compared the energetics of a number of candidate reactions that microorganisms catalyse during the anaerobic oxidation of methane in (i) a coastal lagoon (Cape Lookout Bight, USA), (ii) the deep Black Sea, and (iii) a deep-sea hydrothermal system (Guaymas basin, Gulf of California). Depending on the metabolic pathway and the environment considered, the amount of energy available to the microorganisms varies from 0 to 184 kJ mol,1. At each site, the reactions in which methane is either oxidized to , acetate or formate are generally only favoured under a narrow range of pressure, temperature and solution composition , particularly under low (10,10 m) hydrogen concentrations. In contrast, the reactions involving sulfate reduction with H2, formate and acetate as electron donors are nearly always thermodynamically favoured. Furthermore, the energetics of ATP synthesis was quantified per mole of methane oxidized. Depending on depth, between 0.4 and 0.6 mol of ATP (mol CH4),1 was produced in the Black Sea sediments. The largest potential productivity of 0.7 mol of ATP (mol CH4),1 was calculated for Guaymas Basin, while the lowest values were predicted at Cape Lookout Bight. The approach used in this study leads to a better understanding of the environmental controls on the energetics of AOM. [source] The age of Rubisco: the evolution of oxygenic photosynthesisGEOBIOLOGY, Issue 4 2007E. G. NISBET ABSTRACT The evolutionary history of oxygenesis is controversial. Form I of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in oxygen-tolerant organisms both enables them to carry out oxygenic extraction of carbon from air and enables the competitive process of photorespiration. Carbon isotopic evidence is presented from ~2.9 Ga stromatolites from Steep Rock, Ontario, Canada, ~2.9 Ga stromatolites from Mushandike, Zimbabwe, and ~2.7 Ga stromatolites in the Belingwe belt, Zimbabwe. The data imply that in all three localities the reef-building autotrophs included organisms using Form I Rubisco. This inference, though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesizers first appeared ~2.9 Ga ago, and were abundant 2.7,2.65 Ga ago. Rubisco specificity (its preference for CO2 over O2) and compensation constraints (the limits on carbon fixation) may explain the paradox that despite the inferred evolution of oxygenesis 2.9 Ga ago, the Late Archaean air was anoxic. The atmospheric CO2:O2 ratio, and hence greenhouse warming, may reflect Form I Rubisco's specificity for CO2 over O2. The system may be bistable under the warming Sun, with liquid oceans occurring in either anoxic (H2O with abundant CH4 plus CO2) or oxic (H2O with more abundant CO2, but little CH4) greenhouse states. Transition between the two states would involve catastrophic remaking of the biosphere. Build-up of a very high atmospheric inventory of CO2 in the 2.3 Ga glaciation may have allowed the atmosphere to move up the CO2 compensation line to reach stability in an oxygen-rich system. Since then, Form I Rubisco specificity and consequent compensation limits may have maintained the long-term atmospheric disproportion between O2 and CO2, which is now close to both CO2 and O2 compensation barriers. [source] Biogeochemical modelling of the rise in atmospheric oxygenGEOBIOLOGY, Issue 4 2006M. W. CLAIRE ABSTRACT Understanding the evolution of atmospheric molecular oxygen levels is a fundamental unsolved problem in Earth's history. We develop a quantitative biogeochemical model that simulates the Palaeoproterozoic transition of the Earth's atmosphere from a weakly reducing state to an O2 -rich state. The purpose is to gain an insight into factors that plausibly control the timing and rapidity of the oxic transition. The model uses a simplified atmospheric chemistry (parameterized from complex photochemical models) and evolving redox fluxes in the Earth system. We consider time-dependent fluxes that include organic carbon burial and associated oxygen production, reducing gases from metamorphic and volcanic sources, oxidative weathering, and the escape of hydrogen to space. We find that the oxic transition occurs in a geologically short time when the O2 -consuming flux of reducing gases falls below the flux of organic carbon burial that produces O2. A short timescale for the oxic transition is enhanced by a positive feedback due to decreasing destruction of O2 as stratospheric ozone forms, which is captured in our atmospheric chemistry parameterization. We show that one numerically self-consistent solution for the rise of O2 involves a decline in flux of reducing gases driven by irreversible secular oxidation of the crust caused by time-integrated hydrogen escape to space in the preoxic atmosphere, and that this is compatible with constraints from the geological record. In this model, the timing of the oxic transition is strongly affected by buffers of reduced materials, particularly iron, in the continental crust. An alternative version of the model, where greater fluxes of reduced hydrothermal cations from the Archean seafloor consume O2, produces a similar history of O2 and CH4. When climate and biosphere feedbacks are included in our model of the oxic transition, we find that multiple ,Snowball Earth' events are simulated under certain circumstances, as methane collapses and rises repeatedly before reaching a new steady-state. [source] Determination of isotope fractionation factors and quantification of carbon flow by stable carbon isotope signatures in a methanogenic rice root model systemGEOBIOLOGY, Issue 2 2006H. PENNING ABSTRACT Methanogenic processes can be quantified by stable carbon isotopes, if necessary modeling parameters, especially fractionation factors, are known. Anoxically incubated rice roots are a model system with a dynamic microbial community and thus suitable to investigate principal geochemical processes in anoxic natural systems. Here we applied an inhibitor of acetoclastic methanogenesis (methyl fluoride), calculated the thermodynamics of the involved processes, and analyzed the carbon stable isotope signatures of CO2, CH4, propionate, acetate and the methyl carbon of acetate to characterize the carbon flow during anaerobic degradation of rice roots to the final products CO2 and CH4. Methyl fluoride inhibited acetoclastic methanogenesis and thus allowed to quantify the fractionation factor of CH4 production from H2/CO2. Since our model system was not affected by H2 gradients, the fractionation factor could alternatively be determined from the Gibbs free energies of hydrogenotrophic methanogenesis. The fractionation factor of acetoclastic methanogenesis was also experimentally determined. The data were used for successfully modeling the carbon flow. The model results were in agreement with the measured process data, but were sensitive to even small changes in the fractionation factor of hydrogenotrophic methanogenesis. Our study demonstrates that stable carbon isotope signatures are a proper tool to quantify carbon flow, if fractionation factors are determined precisely. [source] Assessment of methane and nitrous oxide flux from mangroves along Eastern coast of IndiaGEOFLUIDS (ELECTRONIC), Issue 4 2008R. CHAUHAN Abstract Mangroves are considered to be a minor source of greenhouse gases (CH4 and N2O) in pristine environmental condition. However, estimates of efflux suggest that anthropogenic activities have led to a pronounced increase in greenhouse gas emission. Along the east coast of India, mangroves vary substantially in area, physiography and freshwater input, which ultimately modify the biogeochemical processes operating within this ecosystem. An attempt has here been made to elucidate the existing variation and role of climatic variability on the emission of greenhouse gases from mangroves. The flux estimates of CH4 and N2O have been quantified from Bhitarkanika mangrove accounting for spatial and temporal (seasonal) variation. The annual rates were estimated to be 0.096 × 10 9 g CH4 year,1 and 5.8 × 103g N2O year,1 for the whole mangrove area of the east coast of India. Upscaling these estimates yield an annual emission of 1.95 × 10 12 g CH4 year,1 and 1.1 × 10 11 g N2O year,1 from worldwide mangrove areas. The influence of elevated nutrient inputs through anthropogenic influence enhances the emission of greenhouse gas. The present article shows the need to develop an inventory on greenhouse gas flux from mangrove ecosystem. [source] Composition and evolution of fluids during skarn development in the Monte Capanne thermal aureole, Elba Island, central ItalyGEOFLUIDS (ELECTRONIC), Issue 3 2008F. ROSSETTI Abstract We describe the chemistry of the fluids circulating during skarn formation by focusing on fluids trapped in calcsilicate minerals of the inner thermal aureole of the Late Miocene Monte Capanne intrusion of western Elba Island (central Italy). Primary, CH4 -dominant, C-O-H-S-salt fluid inclusions formed during prograde growth of the main skarn-forming mineral phases: grossular/andradite and vesuvianite. The variable phase ratios attest to heterogeneous entrapment of fluid, with co-entrapment of an immiscible hydrocarbon,brine mixture. Chemical elements driving skarn metasomatism such as Na, K, Ca, S and Cl, Fe and Mn were dominantly partitioned into the circulating fluid phase. The high salinity (apparent salinity between 58 and 70 wt% NaCl eq.) and the C-component of the fluids are interpreted as evidence for a composite origin of the skarn-forming fluids that involves both fluids derived from the crystallizing intrusion and contributions from metamorphic devolatilization. Oxidation of a Fe-rich brine in an environment dominated by fluctuation in pressure from lithostatic to hydrostatic conditions (maintained by active crack-sealing) contributed to skarn development. Fluid infiltration conformed to a geothermal gradient of about 100°C km,1, embracing the transition from high-temperature contact metamorphism and fluid-assisted skarn formation (at ca 600°C) to a barren hydrothermal stage (at ca 200°C). [source] Ancient hydrocarbon seeps from the Mesozoic convergent margin of California: carbonate geochemistry, fluids and palaeoenvironmentsGEOFLUIDS (ELECTRONIC), Issue 2 2002K. A. Campbell Abstract More than a dozen hydrocarbon seep-carbonate occurrences in late Jurassic to late Cretaceous forearc and accretionary prism strata, western California, accumulated in turbidite/fault-hosted or serpentine diapir-related settings. Three sites, Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs, were analyzed for their petrographic, geochemical and palaeoecological attributes, and each showed a three-stage development that recorded the evolution of fluids through reducing,oxidizing,reducing conditions. The first stage constituted diffusive, reduced fluid seepage (CH4, H2S) through seafloor sediments, as indicated by Fe-rich detrital micrite, corroded surfaces encrusted with framboidal pyrite, anhedral yellow calcite and negative cement stable isotopic signatures (,13C as low as ,35.5, PDB; ,18O as low as ,10.8, PDB). Mega-invertebrates, adapted to reduced conditions and/or bacterial chemosymbiosis, colonized the sites during this earliest period of fluid seepage. A second, early stage of centralized venting at the seafloor followed, which was coincident with hydrocarbon migration, as evidenced by nonluminescent fibrous cements with ,13C values as low as ,43.7, PDB, elevated ,18O (up to +2.3, PDB), petroleum inclusions, marine borings and lack of pyrite. Throughout these early phases of hydrocarbon seepage, microbial sediments were preserved as layered and clotted, nondetrital micrites. A final late-stage of development marked a return to reducing conditions during burial diagenesis, as implied by pore-associated Mn-rich cement phases with bright cathodoluminescent patterns, and negative ,18O signatures (as low as ,14, PDB). These recurring patterns among sites highlight similarities in the hydrogeological evolution of the Mesozoic convergent margin of California, which influenced local geochemical conditions and organism responses. A comparison of stable carbon and oxygen isotopic data for 33 globally distributed seep-carbonates, ranging in age from Devonian to Recent, delineated three groupings that reflect variable fluid input, different tectono-sedimentary regimes and time,temperature-dependent burial diagenesis. [source] FT-IR measurements of petroleum fluid inclusions: methane, n -alkanes and carbon dioxide quantitative analysisGEOFLUIDS (ELECTRONIC), Issue 1 2001J. Pironon Abstract A recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual fluid inclusion analysis. Fourier transform infrared (FT-IR) microspectroscopy can record compositional information related to gas (CH4 and CO2) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT-IR microspectrometry has been developed to obtain, from individual fluid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Québec City Promontory nappe area was used as standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH4/alkane and CH4/CO2 band area ratios. CH4/alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH4/alkane ratio. Methyl/methylene ratio (CH2/CH3) ratio is obtained following procedures established in previous work. CO2/CH4 concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT-IR quantification and PIT (petroleum inclusion thermodynamic) modelling. [source] Connecting Atmosphere and Wetland: Trace Gas ExchangeGEOGRAPHY COMPASS (ELECTRONIC), Issue 2 2009Peter M. Lafleur This article reviews the exchange of carbon dioxide (CO2) and methane (CH4) gases between wetland and atmosphere, with a primary emphasis on ecosystem-scale fluxes and their environmental controls. It is intended to complement a previous review of wetland energy and water exchanges (Lafleur 2008). It is shown that wetland exchanges of these gases are greatly variable in space and time, especially CH4. Most wetlands appear to be sinks for atmospheric CO2, while almost all are emitters of CH4. The strongest environmental control on the CO2 flux is drought, which often determines whether a wetland will be a net sink or source for atmospheric CO2. Due to complex biochemistry and transport mechanisms, methane efflux from wetlands often ranges over several orders of magnitude within a single wetland and among wetlands, making it difficult to quantify the environmental controls on this flux. The magnitude of gas fluxes is not strongly related to wetland type, which implies that modelling of these fluxes should consider wetlands a continuum and attempt to address processes as they vary along this continuum instead of as discrete entities. Although more research is required into the magnitude, variation and controls on trace gas fluxes in all wetland types, some wetlands (tropical and temperate marshes) are particularly understudied. [source] Soil,atmosphere exchange of CH4, CO, N2O and NOx and the effects of land-use change in the semiarid Mallee system in Southeastern AustraliaGLOBAL CHANGE BIOLOGY, Issue 9 2010IAN GALBALLY Abstract The semiarid and arid zones cover a quarter of the global land area and support one-fifth of the world's human population. A significant fraction of the global soil,atmosphere exchange for climatically active gases occurs in semiarid and arid zones yet little is known about these exchanges. A study was made of the soil,atmosphere exchange of CH4, CO, N2O and NOx in the semiarid Mallee system, in north-western Victoria, Australia, at two sites: one pristine mallee and the other cleared for approximately 65 years for farming (currently wheat). The mean (± standard error) rates of CH4 exchange were uptakes of ,3.0 ± 0.5 ng(C) m,2 s,1 for the Mallee and ,6.0 ± 0.3 ng(C) m,2 s,1 for the Wheat. Converting mallee forest to wheat crop increases CH4 uptake significantly. CH4 emissions were observed in the Mallee in summer and were hypothesized to arise from termite activity. We find no evidence that in situ growing wheat plants emit CH4, contrary to a recent report. The average CO emissions of 10.1 ± 1.8 ng(C) m,2 s,1 in the Mallee and 12.6 ± 2.0 ng(C) m,2 s,1 in the Wheat. The average N2O emissions were 0.5 ± 0.1 ng(N) m,2 s,1 from the pristine Mallee and 1.4 ± 0.3 ng(N) m,2 s,1 from the Wheat. The experimental results show that the processes controlling these exchanges are different to those in temperate systems and are poorly understood. [source] Diurnal and seasonal variation in methane emissions in a northern Canadian peatland measured by eddy covarianceGLOBAL CHANGE BIOLOGY, Issue 9 2010KEVIN D. LONG Abstract Eddy covariance measurements of methane (CH4) net flux were made in a boreal fen, typical of the most abundant peatlands in western Canada during May,September 2007. The objectives of this study were to determine: (i) the magnitude of diurnal and seasonal variation in CH4 net flux, (ii) the relationship between the temporally varying flux rates and associated changes in controlling biotic and abiotic factors, and (iii) the contribution of CH4 emission to the ecosystem growing season carbon budget. There was significant diurnal variation in CH4 emission during the peak of the growing season that was strongly correlated with associated changes in solar radiation, latent heat flux, air temperature and ecosystem conductance to water vapor. During days 181,215, nighttime average CH4 efflux was only 47% of the average midday values. The peak value for daily average CH4 emission rate was approximately 80 nmol m,2 s,1 (4.6 mg CH4 m,2 h,1), and seasonal variation in CH4 flux was strongly correlated with changes in soil temperature. Integrated over the entire measurement period [days 144,269 (late May,late September)], the total CH4 emission was 3.2 g CH4 m,2, which was quite low relative to other wetland ecosystems and to the simultaneous high rate of ecosystem net CO2 sequestration that was measured (18.1 mol CO2 m,2 or 217 g C m,2). We estimate that the negative radiative forcing (cooling) associated with net carbon storage over the life of the peatland (approximately 2200 years) was at least twice the value of positive radiative forcing (warming) caused by net CH4 emission over the last 50 years. [source] | ||||||||||||||||||||||||||||||||||||||||