scholarly journals Acetate turnover and methanogenic pathways in Amazonian lake sediments

2020 ◽  
Vol 17 (4) ◽  
pp. 1063-1069 ◽  
Author(s):  
Ralf Conrad ◽  
Melanie Klose ◽  
Alex Enrich-Prast
Keyword(s):  
Lake Sediments ◽  
Turnover Rates ◽  
Hydrogenotrophic Methanogenesis ◽  
Ch4 Production ◽  
Relative Contribution ◽  
Acetate Methyl ◽  
Syntrophic Oxidation ◽  
Acetoclastic Methanogenesis ◽  
Respiratory Index ◽  
Amazonian Lake

Abstract. Lake sediments in Amazonia are a significant source of CH4, a potential greenhouse gas. Previous studies of sediments using 13C analysis found that the contribution of hydrogenotrophic versus acetoclastic methanogenesis to CH4 production was relatively high. Here, we determined the methanogenic pathway in the same sediments (n=6) by applying 14Cbicarbonate or 2-14Cacetate and confirmed the high relative contribution (50 %–80 %) of hydrogenotrophic methanogenesis. The respiratory index (RI) of 2-14Cacetate, which is 14CO2 relative to 14CH4+14CO2, divided the sediments into two categories, i.e., those with an RI < 0.2 consistent with the operation of acetoclastic methanogenesis and those with an RI > 0.4 showing that a large percentage of the acetate-methyl was oxidized to CO2 rather than reduced to CH4. Hence, part of the acetate was probably converted to CO2 plus H2 via syntrophic oxidation, thus enhancing hydrogenotrophic methanogenesis. This happened despite the presence of potentially acetoclastic Methanosaetaceae in all the sediments. Alternatively, acetate may have been oxidized with a constituent of the sediment organic matter (humic acid) serving as oxidant. Indeed, apparent acetate turnover rates were larger than CH4 production rates except in those sediments with a R<0.2. Our study demonstrates that CH4 production in Amazonian lake sediments was not simply caused by a combination of hydrogenotrophic and acetoclastic methanogenesis but probably involved additional acetate turnover.

scholarly journals Acetate turnover and methanogenic pathways in Amazonian lake sediments

2019 ◽  
Author(s):  
Ralf Conrad ◽  
Melanie Klose ◽  
Alex Enrich-Prast
Keyword(s):  
Lake Sediments ◽  
Turnover Rates ◽  
Hydrogenotrophic Methanogenesis ◽  
Ch4 Production ◽  
Relative Contribution ◽  
Acetate Methyl ◽  
Syntrophic Oxidation ◽  
Aceticlastic Methanogenesis ◽  
Respiratory Index ◽  
Amazonian Lake

Abstract. Lake sediments in Amazonia are a significant source of CH4, a potential greenhouse gas. Previous studies of sediments using 13C analysis found that the contribution of hydrogenotrophic versus aceticlastic methanogenesis to CH4 production was relatively high. Here, we determined the methanogenic pathway in the same sediments (n = 6) by applying [14C]bicarbonate or [2-14C]acetate, and confirmed the high relative contribution (50–80 %) of hydrogenotrophic methanogenesis. The respiratory index (RI) of [2-14C]acetate, which is 14CO2 relative to 14CH4 &amp;plus; 14CO2, divided the sediments into two categories, i.e., those with an RI  0.4 showing that a large percentage of the acetate-methyl was oxidized to CO2 rather than reduced to CH4. Hence, part of the acetate was probably converted to CO2 plus H2 via syntrophic oxidation, thus enhancing hydrogenotrophic methanogenesis. This happened despite the presence of potentially aceticlastic Methanosaetaceae in all the sediments. Alternatively, acetate may have been oxidized with a constituent of the sediment organic matter (humic acid) serving as oxidant. Indeed, apparent acetate turnover rates were larger than CH4 production rates except in those sediments with a R 

scholarly journals Multi-year effect of wetting on CH<sub>4</sub> flux at taiga–tundra boundary in northeastern Siberia deduced from stable isotope ratios of CH<sub>4</sub>

2019 ◽  
Vol 16 (3) ◽  
pp. 755-768 ◽  
Author(s):  
Ryo Shingubara ◽  
Atsuko Sugimoto ◽  
Jun Murase ◽  
Go Iwahana ◽  
Shunsuke Tei ◽  
...  
Keyword(s):  
Water Saturation ◽  
Methane Flux ◽  
Interannual Variations ◽  
Ch4 Emission ◽  
Ch4 Flux ◽  
Ch4 Production ◽  
Year Effect ◽  
Northeastern Siberia ◽  
Order Of Magnitude ◽  
Acetoclastic Methanogenesis

Abstract. The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C, and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70∘37′ N, 147∘55′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

scholarly journals Wetland restoration and methanogenesis: the activity of microbial populations and competition for substrates at different temperatures

2009 ◽  
Vol 6 (6) ◽  
pp. 1127-1138 ◽  
Author(s):  
V. Jerman ◽  
M. Metje ◽  
I. Mandić-Mulec ◽  
P. Frenzel
Keyword(s):  
Methane Emission ◽  
Methane Production ◽  
Iron Reduction ◽  
Carbon Mineralization ◽  
Marsh Soil ◽  
Ch4 Production ◽  
Different Temperatures ◽  
Acetoclastic Methanogenesis ◽  
Diverse Community ◽  
Water Saturated

Abstract. Ljubljana marsh in Slovenia is a 16 000 ha area of partly drained fen, intended to be flooded to restore its ecological functions. The resultant water-logging may create anoxic conditions, eventually stimulating production and emission of methane, the most important greenhouse gas next to carbon dioxide. We examined the upper layer (~30 cm) of Ljubljana marsh soil for microbial processes that would predominate in water-saturated conditions, focusing on the potential for iron reduction, carbon mineralization (CO2 and CH4 production), and methane emission. Methane emission from water-saturated microcosms was near minimum detectable levels even after extended periods of flooding (>5 months). Methane production in anoxic soil slurries started only after a lag period of 84 d at 15°C and a minimum of 7 d at 37°C, the optimum temperature for methanogenesis. This lag was inversely related to iron reduction, which suggested that iron reduction out-competed methanogenesis for electron donors, such as H2 and acetate. Methane production was observed only in samples incubated at 14–38°C. At the beginning of methanogenesis, acetoclastic methanogenesis dominated. In accordance with the preferred substrate, most (91%) mcrA (encoding the methyl coenzyme-M reductase, a key gene in methanogenesis) clone sequences could be affiliated to the acetoclastic genus Methanosarcina. No methanogens were detected in the original soil. However, a diverse community of iron-reducing Geobacteraceae was found. Our results suggest that methane emission can remain transient and low if water-table fluctuations allow re-oxidation of ferrous iron, sustaining iron reduction as the most important process in terminal carbon mineralization.

scholarly journals Effect of Sub-Stoichiometric Fe(III) Amounts on LCFA Degradation by Methanogenic Communities

2020 ◽  
Vol 8 (9) ◽  
pp. 1375
Author(s):  
Ana J. Cavaleiro ◽  
Ana P. Guedes ◽  
Sérgio A. Silva ◽  
Ana L. Arantes ◽  
João C. Sequeira ◽  
...  
Keyword(s):  
Iron Reduction ◽  
Anaerobic Bacteria ◽  
Granular Sludge ◽  
Microbial Interactions ◽  
Methanogenic Activity ◽  
Iron Reducing Bacteria ◽  
Hydrogenotrophic Methanogenesis ◽  
Degrading Bacteria ◽  
Acetoclastic Methanogenesis ◽  
Reducing Bacteria

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H2-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83–89%, 3–6%, and 0.2–10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

scholarly journals Straw application in paddy soil enhances methane production also from other carbon sources

2013 ◽  
Vol 10 (8) ◽  
pp. 14169-14193 ◽  
Author(s):  
Q. Yuan ◽  
J. Pump ◽  
R. Conrad
Keyword(s):  
Priming Effect ◽  
Carbon Sources ◽  
Methanogenic Archaea ◽  
Rice Fields ◽  
Soil Environment ◽  
Traditional Management ◽  
Positive Priming ◽  
Hydrogenotrophic Methanogenesis ◽  
Ch4 Production ◽  
Straw Application

Abstract. Flooded rice fields are an important source of the greenhouse gas methane. Methane is produced from rice straw (RS), soil organic matter (SOM), and rice root organic carbon (ROC). Addition of RS is widely used for ameliorating soil fertility. However, this practice provides additional substrate for CH4 production and results in increased CH4 emission. Here, we found that decomposing RS is not only a substrate of CH4 production, but in addition stimulates CH4 production from SOM and ROC. Apart from accelerating the creation of reduced conditions in the soil environment, RS decomposition exerted a positive priming effect on SOM-derived CH4 production. In particular, hydrogenotrophic methanogenesis from SOM-derived CO2 was stimulated, presumably by H2 released from RS decomposition. On the other hand, the positive priming effect of RS on ROC-derived CH4 production was probably caused by the significant increase of the abundance of methanogenic archaea in the RS treatment compared with the untreated control. Our results show that traditional management of rice residues exerts a positive feedback on CH4 production from rice fields, thus exacerbating its effect on the global CH4 budget.

scholarly journals Thermokarst lake methanogenesis along a complete talik profile

2015 ◽  
Vol 12 (14) ◽  
pp. 4317-4331 ◽  
Author(s):  
J. K. Heslop ◽  
K. M. Walter Anthony ◽  
A. Sepulveda-Jauregui ◽  
K. Martinez-Cruz ◽  
A. Bondurant ◽  
...  
Keyword(s):  
Lake Sediments ◽  
Relative Magnitude ◽  
Thermokarst Lake ◽  
Ch4 Production ◽  
Lake Sediment Core ◽  
Permafrost Soils ◽  
Thawing Permafrost ◽  
Top 40 ◽  
Lake Systems

Abstract. Thermokarst (thaw) lakes emit methane (CH4) to the atmosphere formed from thawed permafrost organic matter (OM), but the relative magnitude of CH4 production in surface lake sediments vs. deeper thawed permafrost horizons is not well understood. We assessed anaerobic CH4 production potentials from various depths along a 590 cm long lake sediment core that captured the entire sediment package of the talik (thaw bulb) beneath the center of an interior Alaska thermokarst lake, Vault Lake, and the top 40 cm of thawing permafrost beneath the talik. We also studied the adjacent Vault Creek permafrost tunnel that extends through ice-rich yedoma permafrost soils surrounding the lake and into underlying gravel. Our results showed CH4 production potentials were highest in the organic-rich surface lake sediments, which were 151 cm thick (mean ± SD: 5.95 ± 1.67 μg C–CH4 g dw−1 d−1; 125.9 ± 36.2 μg C–CH4 g C−1org d−1). High CH4 production potentials were also observed in recently thawed permafrost (1.18 ± 0.61 μg C–CH4g dw−1 d−1; 59.60± 51.5 μg C–CH4 g C−1org d−1) at the bottom of the talik, but the narrow thicknesses (43 cm) of this horizon limited its overall contribution to total sediment column CH4 production in the core. Lower rates of CH4 production were observed in sediment horizons representing permafrost that has been thawing in the talik for a longer period of time. No CH4 production was observed in samples obtained from the permafrost tunnel, a non-lake environment. Our findings imply that CH4 production is highly variable in thermokarst lake systems and that both modern OM supplied to surface sediments and ancient OM supplied to both surface and deep lake sediments by in situ thaw and shore erosion of yedoma permafrost are important to lake CH4 production.

scholarly journals Effect of Temperature on Anaerobic Ethanol Oxidation and Methanogenesis in Acidic Peat from a Northern Wetland

2005 ◽  
Vol 71 (12) ◽  
pp. 8191-8200 ◽  
Author(s):  
Martina Metje ◽  
Peter Frenzel
Keyword(s):  
Volatile Fatty Acids ◽  
Archaeal Community ◽  
Dry Weight ◽  
Effect Of Temperature ◽  
Rrna Gene ◽  
Polymorphism Analysis ◽  
Optimum Temperature ◽  
Hydrogenotrophic Methanogenesis ◽  
Acetoclastic Methanogenesis ◽  
Fe Reduction

ABSTRACT The effects of temperature on rates and pathways of CH4 production and on the abundance and structure of the archaeal community were investigated in acidic peat from a mire in northern Scandinavia (68°N). We monitored the production of CH4 and CO2 over time and measured the turnover of Fe(II), ethanol, and organic 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 25°C (2.3 μmol CH4 · g [dry weight]−1 · day−1), but the activity was relatively high even at 4°C (0.25 μmol CH4 · g [dry weight]−1 · day−1). The theoretical lower limit for methanogenesis was calculated to be at −5°C. The optimum temperature for growth as revealed by real-time PCR was 25°C for both archaea and bacteria. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Hydrogenotrophic methanogenesis accounted for about 80% of the total methanogenesis. Most 16S rRNA gene sequences that were affiliated with methanogens and all McrA sequences clustered with the exclusively hydrogenotrophic order Methanobacteriales, correlating with the prevalence of hydrogenotrophic methanogenesis. Fe reduction occurred parallel to methanogenesis and was inhibited by BES, suggesting that methanogens were involved in Fe reduction. Based upon the observed balance of substrates and thermodynamic calculations, we concluded that the ethanol pool was oxidized to acetate by the following two processes: syntrophic oxidation with methanogenesis (i) as an H2 sink and (ii) as a reductant for Fe(III). Acetate accumulated, but a considerable fraction was converted to butyrate, making volatile fatty acids important end products of anaerobic metabolism.

scholarly journals Stable carbon isotope discrimination and microbiology of methane formation in tropical anoxic lake sediments

2011 ◽  
Vol 8 (3) ◽  
pp. 795-814 ◽  
Author(s):  
R. Conrad ◽  
M. Noll ◽  
P. Claus ◽  
M. Klose ◽  
W. R. Bastos ◽  
...  
Keyword(s):  
Organic Matter ◽  
Lake Sediments ◽  
Carbon Isotope ◽  
Community Composition ◽  
Isotope Fractionation ◽  
Microbial Community Composition ◽  
Methanogenic Archaea ◽  
Methane Formation ◽  
Large Variability ◽  
Ch4 Production

Abstract. Methane is an important end product of degradation of organic matter in anoxic lake sediments. Methane is mainly produced by either reduction of CO2 or cleavage of acetate involving different methanogenic archaea. The contribution of the different methanogenic paths and of the diverse bacteria and archaea involved in CH4 production exhibits a large variability that is not well understood. Lakes in tropical areas, e.g. in Brazil, are wetlands with high potential impact on the global CH4 budget. However, they have hardly been studied with respect to methanogenesis. Therefore, we used samples from 16 different lake sediments in the Pantanal and Amazon region of Brazil to measure production of CH4, CO2, analyze the content of 13C in the products and in intermediately formed acetate, determine the abundance of bacterial and archaeal microorgansisms and their community composition and diversity by targeting the genes of bacterial and archaeal ribosomal RNA and of methyl coenzyme M reductase, the key enzyme of methanogenic archaea. These experiments were done in the presence and absence of methyl fluoride, an inhibitor of acetoclastic methanogenesis. While production rates of CH4 and CO2 were correlated to the content of organic matter and the abundance of archaea in the sediment, values of 13C in acetate, CO2, and CH4 were related to the 13C content of organic matter and to the path of CH4 production with its intrinsic carbon isotope fractionation. Isotope fractionation was small (average 10‰) for conversion of Corg to acetate-methyl, which was hardly further fractionated during CH4 production. However, fractionation was strong for CO2 conversion to CH4 (average 75‰), which generally accounted for >50% of total CH4 production. Canonical correspondence analysis did not reveal an effect of microbial community composition, despite the fact that it exhibited a pronounced variability among the different sediments.

scholarly journals Hydrogenotrophic Methanogenesis Under Alkaline Conditions

2020 ◽  
Vol 11 ◽  
Author(s):  
Richard M. Wormald ◽  
Simon P. Rout ◽  
William Mayes ◽  
Helena Gomes ◽  
Paul N. Humphreys
Keyword(s):  
Cementitious Materials ◽  
Acetate Metabolism ◽  
Acetate Anion ◽  
Methane Generation ◽  
Hydrogenotrophic Methanogenesis ◽  
Alkaline Conditions ◽  
Acetoclastic Methanogenesis ◽  
Syntrophic Acetate Oxidation ◽  
Active Transport System ◽  
Inhibition Studies

A cement-based geological disposal facility (GDF) is one potential option for the disposal of intermediate level radioactive wastes. The presence of both organic and metallic materials within a GDF provides the opportunity for both acetoclastic and hydrogenotrophic methanogenesis. However, for these processes to proceed, they need to adapt to the alkaline environment generated by the cementitious materials employed in backfilling and construction. Within the present study, a range of alkaline and neutral pH sediments were investigated to determine the upper pH limit and the preferred route of methane generation. In all cases, the acetoclastic route did not proceed above pH 9.0, and the hydrogenotrophic route dominated methane generation under alkaline conditions. In some alkaline sediments, acetate metabolism was coupled to hydrogenotrophic methanogenesis via syntrophic acetate oxidation, which was confirmed through inhibition studies employing fluoromethane. The absence of acetoclastic methanogenesis at alkaline pH values (&gt;pH 9.0) is attributed to the dominance of the acetate anion over the uncharged, undissociated acid. Under these conditions, acetoclastic methanogens require an active transport system to access their substrate. The data indicate that hydrogenotrophic methanogenesis is the dominant methanogenic pathway under alkaline conditions (&gt;pH 9.0).

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