CH4 Production Potential Research Articles

Methane Production and Emissions from Four Reclaimed and Pristine Wetlands of Southeastern United States

AbstractWetlands are significant contributors to global CH4 emission. We measured CH4 emissions at two pristine wetlands [Okefenokee swamp and the Everglades (Water Conservation Area 2A)] and two reclaimed wetlands (Sunny Hill Farm and Apopka Marsh) in Southeastern USA, and we attempted to relate emissions to CH4 production rates of the soil and the soil's biological and chemical properties. Methane emissions through cattail [Typha sp.] and waterlily [Nymphaea ordorata (L.)] ranged from 0.09 to 1.7 g CH4 m−2 d−1 and exhibited high spatial and temporal variability. Diffusive flux of CH4 was calculated using dissolved CH4 profiles in the soil pore water and accounted for <5% of the plant‐mediated emissions. Potential CH4 production rates were measured as a function of depth using soil samples obtained at 2‐cm increments. Methane production rates were the same order of magnitude at all sites (<1–70 ng CH4‐C g−1 soil C d−1) and were highest in the surface soils (0–6 cm) at three of the wetland sites, indicating that the predominant source of C available to methanogens was in the surface soils. Methane production rates in the top 24 cm ranged from 0.3 to 1.1 g CH4 m−2 d−1 and annual C losses due to anaerobic decomposition accounted for between 0.68 and 3.7% of the total C in the surface 24‐cm soil depth. Methane production was observed at sites with porewater SO4 concentrations of up to 20 mg SO4‐S L−1, suggesting that methanogenesis occurred in the same soil layer as SO4 reduction, possibly in microsites where SO4 concentration was depleted.

Ecosystem and physiological controls over methane production in northern wetlands

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 (∂CH4/∂EtOH = 0.9–2.3mg g−1) and weakly in the acidic bogs with wide C:N and lignin:N ratios (∂CH4/∂EtOH = −0.04–0.02 mg g−1). Observed Q10 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.

Denitrification and methane production in sediment of Hamilton Harbour (Canada)

Systematic sampling of 21 sites covering Hamilton Harbour (Lake Ontario, Canada) was carried out during the summer in 1990 and 1991 in order to study how well environmental factors, such as O2, NO 3 (-) , and organic carbon, and the spatial structure can explain observed variation of potential denitrification, CH4 and CO2 production, as well as N2 fixation in sediment slurries. Using canonical redundancy analysis and an extension of this method to partial out the variance into spatial and environmental components, we found that most of the explained fraction of potential microbial activities (70-90%) was accounted for by the significant environmental variables (NH 4 (+) , particulate carbon, dissolved organic carbon, dissolved O2, depth, and temperature) and not much by the spatial polynomial trend surface. We found significant path coefficients (0.53 and 0.57 in 1990 and 1991) between CO2 production and potential denitrification, which suggests that denitrifiers are dependent upon a heterotrophic bacterial population for directly assimilable carbon sources. We also found significant path coefficients between particulate carbon and both CH4 production (0.67 and 0.33) and CO2 production (0.50 and 0.38), while significant path coefficients were also found between dissolved organic carbon and CO2 production (0.34 and 0.47). We conclude that beside well-known abiotic factors such as O2, NO 3 (-) , and organic carbon, a biotic factor involved in carbon metabolism may be important in explaining the spatial variation of denitrification capacity in the sediment of Hamilton Harbour.

Methane flux from drained northern peatlands: Effect of a persistent water table lowering on flux

Measurements of CH4 flux from drained and undrained sites in three northern Ontario peatlands (a treed fen, a forested bog, and a treed bog) were made from the beginning of May to the end of October 1991. In the drained portions, the water table had been lowered between 0.1 and 0.5 m, compared to the water table of the undrained portion of the peatlands. The mean seasonal CH4 flux from the undrained portions of three peatlands was small, ranging from 0 to 8 mg m−2d−1, but similar to the CH4 flux from other treed and forested northern peatlands. The mean seasonal CH4 flux from the drained portion of the peatlands was either near zero or slightly negative (i.e.,uptake): fluxes ranged from 0.1 to −0.4 mg m−2 d−1. Profiles of CH4 in the air‐filled pores in the unsaturated zone, and the water‐filled pores of the saturated zone of the peat at the undrained sites, showed that all the CH4 produced at depth was consumed within 0.2 m of the water table and that atmospheric CH4 was consumed in the upper 0.15 m of the peatland. On the basis of laboratory incubations of peat slurries to determine CH4 production and consumption potentials, the lowering of the water table eliminated the near‐surface zone of CH4 production that existed in the undrained peatland. However, drainage did not alter significantly the potential for CH4 oxidation between the water table and peatland surface but increased the thickness of the layer over which CH4 oxidation could take place. These changes occurred with a drop in the mean summer water table of only 0.1 m (from −0.2 to −0.3 m) suggesting that only a small negative change in soil moisture would be required to significantly reduce CH4 flux from northern peatlands.

Sensitivity of methanogenic bacteria from paddy soil to oxygen and desiccation

The effects of combinations of desiccation and exposure to O2 were studied in pure cultures of Methanosarcina barkeri strain Fusaro and in a new Methanosarcina strain and a new Methanobacterium strain which were both isolated from dry oxic paddy soil. Incubation of bacterial suspensions under air for 200 min resulted in a decreased potential to produce CH4, but not in a decreased viability. The inhibitory effect of O2 slightly increased with increased salt concentration. Desiccation of bacterial suspensions under N2 resulted in reduction of viability to 10% and of potential CH4 production to 0.6%. Desiccation of bacterial suspensions under air resulted in a larger decrease of both viability (0.5%) and potential CH4 production (0.03%). This decrease was smaller at rapid compared to slow desiccation. Survival and potential CH4 production were further inhibited when the suspension was dried in the presence of sand grains or glass beads coated with FeS or FeNH4PO4. However, survival and potential CH4 production increased dramatically in the presence of pyrite (FeS2) grains. Then, as much as 10% of the initial methanogenic population survived oxic desiccation. This relatively good resistance is in agreement with observations that methanogens in rice fields survive the periods when the paddy soil is dry and oxic.

Sensitivity of methanogenic bacteria from paddy soil to oxygen and desiccation

The effects of combinations of desiccation and exposure to O2 were studied in pure cultures of Methanosarcina barkeri strain Fusaro and in a new Methanosarcina strain and a new Methanobacterium strain which were both isolated from dry oxic paddy soil. Incubation of bacterial suspensions under air for 200 min resulted in a decreased potential to produce CH4, but not in a decreased viability. The inhibitory effect of O2 slightly increased with increased salt concentration. Desiccation of bacterial suspensions under N2 resulted in reduction of viability to 10% and of potential CH4 production to 0.6%. Desiccation of bacterial suspensions under air resulted in a larger decrease of both viability (0.5%) and potential CH4 production (0.03%). This decrease was smaller at rapid compared to slow desiccation. Survival and potential CH4 production were further inhibited when the suspension was dried in the presence of sand grains or glass beads coated with FeS or FeNH4PO4. However, survival and potential CH4 production increased dramatically in the presence of pyrite (FeS2) grains. Then, as much as 10% of the initial methanogenic population survived oxic desiccation. This relatively good resistance is in agreement with observations that methanogens in rice fields survive the periods when the paddy soil is dry and oxic.

Estimation of Potential CO2 and CH4 Production in Japanese Paddy Fields

Estimation of Potential CO2 and CH4 Production in Japanese Paddy Fields

The influence of clay minerals, oxides, and humic matter on the methylation and demethylation of mercury by micro‐organisms in freshwater sediments

AbstractLaboratory experiments and analysis of field samples showed that clay minerals, Fe and Mn oxides, and humic matter (colloids) have complex and often dramatic effects on the microbial methylation and demethylation of Hg, and on other microbial activities, in lake sediments. Depending on the nature, abundance, and surface chemistry of the colloids, the source of the sediment, the nature of the microbes, and synergistic/antagonistic effects of environmental variables, the colloids either strongly inhibited or stimulated the Hg transformations, had little or no effect, or alternated in their effects. Most of the results suggest specific effects on particular kinds of microbes, and are not attributable to general inhibition or stimulation of microbial growth or to effects due to the binding of Hg by the colloids. The colloids probably alter the species composition of the microbial community and affect the course of ecological succession, upsetting the dynamic balance between methylation and demethylation and causing alternate increases and decreases in methyl mercury (CH3Hg+) levels along with changes in other indicators of microbial activity [CO2 and CH4 production and oxidationreduction potential (Eh)].The role of clays was critically dependent on surface coatings. Clays often interfered with methylation (while in some cases strongly promoting subsequent demethylation); but iron oxide (FeOOH) often promoted methylation, and FeOOH coatings on clay tended to counterbalance the negative influence of the clay. Removal of oxide coatings depressed both methylation and demethylation. Manganese oxide (MnOOH) coatings sometimes promoted methylation, but larger amounts of MnOOH (unlike FeOOH) strongly suppressed methylation. On addition of organic nutrients, oxide coatings enhanced methylation and impeded demethylation; without nutrient enrichment, the reverse tended to occur. Humic matter in solution tended to stimulate methylation; but humic coatings on clay impeded methylation and fostered demethylation. Thus, the effects of natural colloids on Hg speciation are vitally important but variable, inconsistent, and not altogether predictable.

Methane production by domestic animals, wild ruminants, other herbivorous fauna, and humans

A detailed assessment of global methane production through enteric fermentation by domestic animals and humans is presented. Measured relations between feed intake and methane yields for animal species are combined with population statistics to deduce a current yearly input of methane to the atmosphere of 74 Tg (1 Tg = 1012 g). with an uncertainty of about 15%. Of this, cattle contribute about 74%. Buffalos and sheep each account for 8-9%, and the remainder stems from camels, mules and asses, pigs, and horses. Human CH4 production is probably less than 1 Tg per year. The mean annual increase in CH4 emission from domestic animals and humans over the past 20 years has been 0.6 Tg, or 0.75% per year. Population figures on wild ruminants are so uncertain that calculated CH, emissions from this source may range between 2 Tg and 6 Tg per year. Current CH4 emission by domestic and wild animals is estimated to be about 78 Tg, representing 15-25% of the total CH4 released to the atmosphere from all sources. The likely CH4 production from domestic animals in 1890 was about 17 Tg, so that this source has increased by a factor of 4.4.A brief tentative discussion is also given on the potential CH4 production by other herbivorous fauna, especially insects. Their total CH4 production probably does not exceed 30 Tg annually.