Evolution of stable carbon isotope compositions for methane and carbon dioxide in freshwater wetlands and other anaerobic environments

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

doi:10.1016/s0016-7037(99)00321-x

Cited by 157 publications

(149 citation statements)

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“…2) is consistent with the understanding that these shifts are associated with increasing organic matter lability (12,14,15). A likely mechanism for this effect is the loss of organic acids along the thaw progression (Fig.…”

Section: Discussionsupporting

confidence: 85%

“…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%

mentioning

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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Section: Discussionsupporting

confidence: 85%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

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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“…Impacts on recent photosynthate are therefore not the main source for CH 4 production in this wet heath, at least not in early August, suggesting that the hydrogenotrophic pathway using less recent C sources rather than the acetoclastic pathway using more labile organic C may have been more prevalent in CH 4 production in the mesocosms (e.g. Hornibrook et al, 2000). This was not clearly supported by the apparent fractionation factors of 1.055 and 1.057 for pore water observed at 20 cm and 30 cm depth, as they are borderline in indicating the dominance of either pathway (Whiticar et al, 1986;Whiticar, 1999;Conrad, 2005;Holmes et al, 2015).…”

Section: Plant-mediated Ozone Responsesmentioning

confidence: 94%

How does elevated ozone reduce methane emissions from peatlands?

Toet

Oliver

Ineson

et al. 2017

Science of The Total Environment

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CO₂ and CH₄ isotope compositions and production pathways in a tropical peatland

Holmes

Chanton

Tfaily

et al. 2015

Global Biogeochemical Cycles

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While it is widely recognized that peatlands are important in the global carbon cycle, there is limited information on belowground gas production in tropical peatlands. We measured pore water methane (CH 4 ) and carbon dioxide (CO 2 ) concentrations and δ 13 C isotopic composition and CH 4 and CO 2 production rates in peat incubations from the Changuinola wetland in Panama. Our most striking finding was that CH 4 was depleted in 13 C (À94‰ in pore water and produced at À107‰ in incubated peat) relative to CH 4 found in most temperate and northern wetlands, potentially impacting the accuracy of approaches that use carbon isotopes to constrain global mass balance estimates. Fractionation factors between CH 4 and CO 2 showed that hydrogenotrophic methanogenesis was the dominant CH 4 production pathway, with up to 100% of the CH 4 produced via this route. Far more CO 2 than CH 4 (7 to 100X) was measured in pore water, due in part to loss of CH 4 through ebullition or oxidation and to the production of CO 2 from pathways other than methanogenesis. We analyzed data on 58 wetlands from the literature to determine the dominant factors influencing the relative proportions of CH 4 produced by hydrogenotrophic and acetoclastic methanogenesis and found that a combination of environmental parameters including pH, vegetation type, nutrient status, and latitude are correlated to the dominant methanogenic pathway. Methane production pathways in tropical peatlands do not correlate with these variables in the same way as their more northerly counterparts and thus may be differently affected by climate change.

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Evolution of stable carbon isotope compositions for methane and carbon dioxide in freshwater wetlands and other anaerobic environments

Cited by 157 publications

References 58 publications

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

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

How does elevated ozone reduce methane emissions from peatlands?

CO₂ and CH₄ isotope compositions and production pathways in a tropical peatland

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Evolution of stable carbon isotope compositions for methane and carbon dioxide in freshwater wetlands and other anaerobic environments

Cited by 157 publications

References 58 publications

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

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

How does elevated ozone reduce methane emissions from peatlands?

CO2 and CH4 isotope compositions and production pathways in a tropical peatland

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CO₂ and CH₄ isotope compositions and production pathways in a tropical peatland