Spatial distribution of microbial methane production pathways in temperate zone wetland soils: Stable carbon and hydrogen isotope evidence

Hornibrook, Edward R. C.; Longstaffe, Frederick J.; Fyfe, W. S.

doi:10.1016/s0016-7037(96)00368-7

Cited by 180 publications

(168 citation statements)

References 53 publications

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“…To a large extent, dD-CH 4 is controlled by dD water . For example, , Burke et al (1988), Sugimoto & Wada (1995), Hornibrook et al (1997), Waldron et al (1999) and Whiticar (1999) and others showed that in methanogenesis the dD-CH 4 is dependent on the MR or CR pathway, i.e. if the hydrogen is transferred from organic substrates or H 2 .…”

Section: Source Components Of Pih Yd-pb and Lgm Global Methane Invenmentioning

confidence: 99%

Constraining past global tropospheric methane budgets with carbon and hydrogen isotope ratios in ice

Whiticar

Schaefer

2007

Phil. Trans. R. Soc. A.

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Upon closer inspection, the classical view of the synchronous relationship between tropospheric methane mixing ratio and Greenland temperature observed in ice samples reveals clearly discernable variations in the magnitude of this response during the Late Pleistocene (!50 kyr BP). During the Holocene this relationship appears to decouple, indicating that other factors have modulated the methane budget in the past 10 kyr BP. The d 13 CH 4 and dD-CH 4 of tropospheric methane recorded in ice samples provide a useful constraint on the palaeomethane budget estimations. Anticipated changes in palaeoenvironmental conditions are recorded as changes in the isotope signals of the methane precursors, which are then translated into past global d 13 CH 4 and dD-CH 4 signatures. We present the first methane budgets for the late glacial period that are constrained by dual stable isotopes. The overall isotope variations indicate that the Younger Dryas ( YD) and Preindustrial Holocene have methane that is 13 C-and 2 H-enriched, relative to Modern. The shift is small for d 13 CH 4 (approx. 1‰) but greater for dD-CH 4 (approx. 9‰). The YD d 13 CH 4 -dD-CH 4 record shows a remarkable relationship between them from 12.15 to 11.52 kyr BP. The corresponding C-and H-isotope mass balances possibly indicate fluctuating emissions of thermogenic gas. This d 13 CH 4 -dD-CH 4 relationship breaks down during the YD-Preboreal transition. In both age cases, catastrophic releases of hydrates with Archaeal isotope signatures can be ruled out. Thermogenic clathrate releases are possible during the YD period, but so are conventional natural gas seepages.

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Section: Source Components Of Pih Yd-pb and Lgm Global Methane Invenmentioning

confidence: 99%

Constraining past global tropospheric methane budgets with carbon and hydrogen isotope ratios in ice

Whiticar

Schaefer

2007

Phil. Trans. R. Soc. A.

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“…Distinguishing these controls and further mapping them is therefore essential for predicting future changes in CH 4 formation under changing environmental conditions. Several studies have suggested that the proportion of CH 4 produced by acetate cleavage relative to CO 2 reduction is likely to increase with increasing pH (19,20) and organic matter reactivity (12,14,15), but direct evidence of the latter is lacking.In this study, we tested the hypotheses that (i) organic matter reactivity increases with permafrost thaw due to thaw-induced subsidence and associated shifts in hydrology and plant community (21), and (ii) CH 4 production shifts from hydrogenotrophic to acetoclastic due to this increase in organic matter reactivity. We assessed organic matter reactivity along a distinct chronosequence of permafrost thaw stages with differing plant community and hydrology by performing anaerobic incubations of peat collected along this sequence.…”

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confidence: 99%

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confidence: 99%

“…The reduction of CO 2 with H 2 (hydrogenotrophic production) generally produces CH 4 more depleted in 13 C (δ 13 C = −110 to −60‰) than CH 4 produced by the cleavage of acetate into CH 4 and CO 2 (δ 13 C = −70 to −30‰) (10,11,(13)(14)(15). Due to the coproduction or utilization of CO 2 during CH 4 production (10-12, 16, 17), δ 13 C CH4 also depends on δ 13 C CO2 , so we use the more robust parameter α C (10) to represent the isotopic separation between CH 4 and CO 2 .…”

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confidence: 99%

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Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production

Hodgkins¹,

Tfaily²,

McCalley

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

288

362

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Carbon release due to permafrost thaw represents a potentially major positive climate change feedback. The magnitude of carbon loss and the proportion lost as methane (CH 4 ) vs. carbon dioxide (CO 2 ) depend on factors including temperature, mobilization of previously frozen carbon, hydrology, and changes in organic matter chemistry associated with environmental responses to thaw. While the first three of these effects are relatively well understood, the effect of organic matter chemistry remains largely unstudied. To address this gap, we examined the biogeochemistry of peat and dissolved organic matter (DOM) along a ∼40-y permafrost thaw progression from recently-to fully thawed sites in Stordalen Mire (68.35°N,19.05°E), a thawing peat plateau in northern Sweden. Thaw-induced subsidence and the resulting inundation along this progression led to succession in vegetation types accompanied by an evolution in organic matter chemistry. Peat C/N ratios decreased whereas humification rates increased, and DOM shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH 4 and CO 2 production potentials, higher relative CH 4 /CO 2 ratios, and a shift in CH 4 production pathway from CO 2 reduction to acetate cleavage. These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH 4 . This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.H igh-latitude soils in the Northern Hemisphere contain an estimated 1,400-1,850 petagrams (Pg) of carbon, of which ∼277 Pg is in peatlands within the permafrost zone (1, 2). This quantity of 277 Pg represents over one-third of the carbon stock in the atmosphere (ca. 800 Pg) (3). The fate of this carbon in a warming climate-i.e., the responses of net carbon balance and CH 4 emissions-is important in predicting climate feedbacks of permafrost thaw. Although northern peatlands are currently a net carbon sink, and have been since the end of the last glaciation, they are a net source of CH 4 (4, 5), emitting 0.046-0.09 Pg of carbon as CH 4 per year (4, 6, 7). Due to CH 4 's disproportionate global warming potential (33× CO 2 for 1 kg CH 4 vs. 1 kg CO 2 at a 100-y timescale) (8), this is equivalent to 6-12% of annual fossil fuel emissions of CO 2 (8.7 Pg of C) (9). The thaw of permafrost peatlands may alter their CH 4 and CO 2 emissions due to mobilization of formerly frozen carbon, higher temperatures, altered redox conditions, and evolving organic matter chemistry. Changes in carbon emissions, and in CH 4 emission in particular, could have potentially significant climate impacts. CH 4 is produced by two primary mechanisms (10-12),...

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“…This availability of CO 2 at high concentrations, along with stable temperatures at depth, could make CO 2 a source of year-round CH 4 production. Reduction of CO 2 by hydrogenotrophic methanogens, using H 2 from fermentation of polysaccharides, is a favored pathway of CH 4 at depth (Hornibrook et al, 1997). These two pathways of CH 4 production result from fermentation of labile carbon and could be enhanced with a higher availability of labile carbon.…”

Section: Gas and Water Samplesmentioning

confidence: 99%

Using hydrologic measurements to investigate free-phase gas ebullition in a Maine peatland, USA

Bon

Reeve

Slater

et al. 2014

Hydrol. Earth Syst. Sci.

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Abstract. Northern peatlands cover more than 350 million ha and are an important source of methane (CH 4 ) and other biogenic gases contributing to climate change. Free-phase gas (FPG) accumulation and episodic release has recently been recognized as an important mechanism for biogenic gas flux from peatlands. It is likely that gas production and groundwater flow are interconnected in peatlands: groundwater flow influences gas production by regulating geochemical conditions and nutrient supply available for methanogenesis, while FPG influences groundwater flow through a reduction in peat permeability and by creating excess pore water pressures. Water samples collected from three well sites at Caribou Bog, Maine, show substantial dissolved CH 4 (5-16 mg L −1 ) in peat waters below 2 m depth and an increase in concentrations with depth. This suggests production and storage of CH 4 in deep peat that may be episodically released as FPG. Two min increment pressure transducer data reveal approximately 5 cm fluctuations in hydraulic head from both deep and shallow peat that are believed to be indicative of FPG release. FPG release persists up to 24 h during decreasing atmospheric pressure and a rising water table. Preferential flow is seen towards an area of relatively lower hydraulic head associated with the esker and pool system. Increased CH 4 concentrations are also found at the depth of the esker crest, suggesting that the high permeability esker is acting as a conduit for groundwater flow, driving a downward transport of labile carbon, resulting in higher rates of CH 4 production.

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Spatial distribution of microbial methane production pathways in temperate zone wetland soils: Stable carbon and hydrogen isotope evidence

Cited by 180 publications

References 53 publications

Constraining past global tropospheric methane budgets with carbon and hydrogen isotope ratios in ice

Constraining past global tropospheric methane budgets with carbon and hydrogen isotope ratios in ice

Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production

Using hydrologic measurements to investigate free-phase gas ebullition in a Maine peatland, USA

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