Methane Concentration and Stable Isotope Distribution as Evidence of Rhizospheric Processes: Comparison of a Fen and Bog in the Glacial Lake Agassiz Peatland Complex

Chasar, L. S.

doi:10.1006/anbo.2000.1172

Cited by 130 publications

(169 citation statements)

References 58 publications

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“…Generally, methane concentrations measured in this study were lower than previously observed in bog mesocosms (Blodau and Moore, 2003a) but were comparable to other fen soils (Chasar et al, 2000;Smemo and Yavitt, 2006). The isotopic composition of methane in W-V was in accordance with δ 13 C CH 4 reported in other studies, particularly if sedges were present.…”

Section: Respiration and Methanogenesissupporting

confidence: 88%

“…Additionally, values of α C were still in the overlap range of fractionation factors from both processes (Whiticar, 1999;Conrad, 2005). The measured δ 13 C CH 4 values also coincide well with data from other fens where Carex species were found (Chasar et al, 2000;Popp et al, 1999), as was the case in W-V.…”

Section: Impact Of Drying and Rewetting On Methanogenic Pathwayssupporting

confidence: 84%

“…The isotopic composition of methane in W-V was in accordance with δ 13 C CH 4 reported in other studies, particularly if sedges were present. Values observed in DW-V and DW-D were considerably lighter in isotopic composition than previously reported (Chasar et al, 2000;Lansdown et al, 1992;Popp et al, 1999;Waldron et al, 1999). In the wet treatment W-V, concentrations of methane and total dissolved carbon dioxide reached a steady state and were high enough to sustain measurable emission.…”

Section: Respiration and Methanogenesiscontrasting

confidence: 50%

“…A δ 13 C CH 4 of approximately −70‰ of the methane formed in the shallow depths of DW-V and α C =1.05-1.07 thus supported that the methane to a great extent was formed by hydrogenotrophic methanogens and not by acetotrophs (Whiticar, 1999). This is in contrast to prior studies, reporting a predominance of acetotrophs in shallow peats (Chasar et al, 2000;Popp et al, 1999;Hornibrook et al, 2000a). Predominance of hydrogenotrophs would further be supported by higher H 2 concentrations at shallow depths in this treatment.…”

Section: Impact Of Drying and Rewetting On Methanogenic Pathwayssupporting

confidence: 40%

“…In this study, this was presumably caused by the drying/rewetting event, which resulted in low hydrogen concentrations due to the presence of other electron acceptors in the bulk peat. Most α C values calculated for levels above the water table were in an overlap range of α C from hydrogenotrophic and acetoclastic methanogenesis (Whiticar, 1999;Chasar et al, 2000), and most values of α C for the latter pathway summarized by Conrad (2005) were still lower. A δ 13 C CH 4 of approximately −70‰ of the methane formed in the shallow depths of DW-V and α C =1.05-1.07 thus supported that the methane to a great extent was formed by hydrogenotrophic methanogens and not by acetotrophs (Whiticar, 1999).…”

Section: Impact Of Drying and Rewetting On Methanogenic Pathwaysmentioning

confidence: 97%

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Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

2008

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Abstract. Peatlands contain a carbon stock of global concern and significantly contribute to the global methane burden. The impact of drought and rewetting on carbon cycling in peatland ecosystems is thus currently debated. We studied the impact of experimental drought and rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing drought for 50 days. In one of the mesocosms, vegetation had been removed. Net production of CH4 was calculated from mass balances in the peat and emission using static chamber measurements. Results were compared to 13C isotope budgets of CO2 and CH4 and energy yields of acetoclastic and hydrogenotrophic methanogenesis. Drought retarded methane production after rewetting for days to weeks and promoted methanotrophic activity. Based on isotope and flux budgets, aerobic soil respiration contributed 32–96% in the wet treatment and 86–99% in the other treatments. Drying and rewetting did not shift methanogenic pathways according to δ13C ratios of CH4 and CO2. Although δ13C ratios indicated a prevalence of hydrogenotrophic methanogenesis, free energies of this process were small and often positive on the horizon scale. This suggests that methane was produced very locally. Fresh plant-derived carbon input apparently supported respiration in the rhizosphere and sustained methanogenesis in the unsaturated zone, according to a 13C-CO2 labelling experiment. The study documents that drying and rewetting in a rich fen soil may have little effect on methanogenic pathways, but result in rapid shifts between methanogenesis and methanotrophy. Such shifts may be promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis occurred locally even when conditions were not conducive for this process in the bulk peat.

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Section: Respiration and Methanogenesissupporting

confidence: 88%

Section: Impact Of Drying and Rewetting On Methanogenic Pathwayssupporting

confidence: 84%

Section: Respiration and Methanogenesiscontrasting

confidence: 50%

Section: Impact Of Drying and Rewetting On Methanogenic Pathwayssupporting

confidence: 40%

Section: Impact Of Drying and Rewetting On Methanogenic Pathwaysmentioning

confidence: 97%

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Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

2008

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Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

Throckmorton

Heikoop

Newman

et al. 2015

Global Biogeochemical Cycles

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Arctic soils contain a large pool of terrestrial C and are of interest due to their potential for releasing significant carbon dioxide (CO2) and methane (CH4) to the atmosphere. Due to substantial landscape heterogeneity, predicting ecosystem‐scale CH4 and CO2 production is challenging. This study assessed dissolved inorganic carbon (DIC = Σ (total) dissolved CO2) and CH4 in watershed drainages in Barrow, Alaska as critical convergent zones of regional geochemistry, substrates, and nutrients. In July and September of 2013, surface waters and saturated subsurface pore waters were collected from 17 drainages. Based on simultaneous DIC and CH4 cycling, we synthesized isotopic and geochemical methods to develop a subsurface CH4 and DIC balance by estimating mechanisms of CH4 and DIC production and transport pathways and oxidation of subsurface CH4. We observed a shift from acetoclastic (July) toward hydrogenotropic (September) methanogenesis at sites located toward the end of major freshwater drainages, adjacent to salty estuarine waters, suggesting an interesting landscape‐scale effect on CH4 production mechanism. The majority of subsurface CH4 was transported upward by plant‐mediated transport and ebullition, predominantly bypassing the potential for CH4 oxidation. Thus, surprisingly, CH4 oxidation only consumed approximately 2.51 ± 0.82% (July) and 0.79 ± 0.79% (September) of CH4 produced at the frost table, contributing to <0.1% of DIC production. DIC was primarily produced from respiration, with iron and organic matter serving as likely e‐ acceptors. This work highlights the importance of spatial and temporal variability of CH4 production at the watershed scale and suggests broad scale investigations are required to build better regional or pan‐Arctic representations of CH4 and CO2 production.

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The relative importance of methanogenesis in the decomposition of organic matter in northern peatlands

et al. 2015

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Using an isotope-mass balance approach and assuming the equimolar production of CO 2 and CH 4 from methanogenesis (e.g., anaerobic decomposition of cellulose), we calculate that the proportion of total CO 2 production from methanogenesis varies from 37 to 83% across a variety of northern peatlands. In a relative sense, methanogenesis was a more important pathway for decomposition in bogs (80 ± 13% of CO 2 production) than in fens (64 ± 5.7% of CO 2 production), but because fens contain more labile substrates they may support higher CH 4 production overall. The concentration of CO 2 produced from methanogenesis (CO 2-meth ) can be considered equivalent to CH 4 concentration before loss due to ebullition, plant-mediated transport, or diffusion. Bogs produced slightly less CO 2-meth than fens (2.9 ± 1.3 and 3.7 ± 1.4 mmol/L, respectively). Comparing the quantity of CH 4 present to CO 2-meth , fens lost slightly more CH 4 than bogs (89 ± 2.8% and 82 ± 5.3%, respectively) likely due to the presence of vascular plant roots. In collapsed permafrost wetlands, bog moats produced half the amount of CO 2-meth (0.8 ± 0.2 mmol/L) relative to midbogs (1.6 ± 0.6 mmol/L) and methanogenesis was less important (42 ± 6.6% of total CO 2 production relative to 55 ± 8.1%). We hypothesize that the lower methane production potential in collapsed permafrost wetlands occurs because recently thawed organic substrates are being first exposed to the initial phases of anaerobic decomposition following collapse and flooding. Bog moats lost a comparable amount of CH 4 as midbogs (63 ± 7.0% and 64 ± 9.3%).

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Methane Concentration and Stable Isotope Distribution as Evidence of Rhizospheric Processes: Comparison of a Fen and Bog in the Glacial Lake Agassiz Peatland Complex

Cited by 130 publications

References 58 publications

Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

The relative importance of methanogenesis in the decomposition of organic matter in northern peatlands

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Methane Concentration and Stable Isotope Distribution as Evidence of Rhizospheric Processes: Comparison of a Fen and Bog in the Glacial Lake Agassiz Peatland Complex

Cited by 130 publications

References 58 publications

Fluxes and &lt;sup&gt;13&lt;/sup&gt;C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

Fluxes and &lt;sup&gt;13&lt;/sup&gt;C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

The relative importance of methanogenesis in the decomposition of organic matter in northern peatlands

Contact Info

Product

Resources

About

Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought