Effect of seasonal changes in the pathways of methanogenesis on the δ13C values of pore water methane in a Michigan peatland

G. Brooks Avery, Robert David Shannon, Jeffrey R. White, Christophers Martens, Marc J. Alperin

Research output: Contribution to journalArticle

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Abstract

The δ13C value of pore water methane produced in a Michigan peatland varied by 11% during the year. This isotopic shift resulted from large seasonal changes in the pathways of methane production. On the basis of mass balance calculations, the δ13C value of methane from CO2 reduction (average =-71.4 ± 1.8%) was depleted in 13C compared to that produced from acetate (-44.4 ± 8.2%o). The dissolved methane at the site remained heavy (approximately-51%o) during most of the year. Tracer experiments using 14C-labeled CO2 indicated that during January 110 ± 25% of the methane was produced by CO2 reduction. Because of low-methane production rates during the winter, this C-depleted methane had only a slight effect on the isotopic composition of the methane pool. In early spring when peat temperatures and methane production rates increased, the δ13C value of the dissolved methane in shallow peat was influenced by the isotopically light methane and approached-61‰. Peat incubation experiments conducted at 15°C in May and June (when the peat reaches its maximum temperature) indicated that an average of 84 ± 9% of the methane production was from acetate and had an average δ13C value of-48.7 ± 5.6‰. Rising acetate concentrations during April-May (approaching 1 mmol L-1(mM)) followed by a rapid decrease in acetate concentrations during May-June reflected the shift toward methane production dominated by acetate fermentation. During this period, dissolved methane in shallow peat at the site returned to heavier values (approximately-5 l%o) similar to that produced in the incubation experiments.

Original languageEnglish (US)
Pages (from-to)475-484
Number of pages10
JournalGlobal Biogeochemical Cycles
Volume13
Issue number2
DOIs
StatePublished - Jun 1 1999

Fingerprint

Methane
methanogenesis
peatland
porewater
methane
Water
Peat
peat
acetate
Acetates
effect
incubation
experiment
Experiments
Fermentation
fermentation
mass balance
isotopic composition

All Science Journal Classification (ASJC) codes

  • Global and Planetary Change
  • Environmental Chemistry
  • Environmental Science(all)
  • Atmospheric Science

Cite this

Avery, G. Brooks ; Shannon, Robert David ; White, Jeffrey R. ; Martens, Christophers ; Alperin, Marc J. / Effect of seasonal changes in the pathways of methanogenesis on the δ13C values of pore water methane in a Michigan peatland. In: Global Biogeochemical Cycles. 1999 ; Vol. 13, No. 2. pp. 475-484.
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abstract = "The δ13C value of pore water methane produced in a Michigan peatland varied by 11{\%} during the year. This isotopic shift resulted from large seasonal changes in the pathways of methane production. On the basis of mass balance calculations, the δ13C value of methane from CO2 reduction (average =-71.4 ± 1.8{\%}) was depleted in 13C compared to that produced from acetate (-44.4 ± 8.2{\%}o). The dissolved methane at the site remained heavy (approximately-51{\%}o) during most of the year. Tracer experiments using 14C-labeled CO2 indicated that during January 110 ± 25{\%} of the methane was produced by CO2 reduction. Because of low-methane production rates during the winter, this C-depleted methane had only a slight effect on the isotopic composition of the methane pool. In early spring when peat temperatures and methane production rates increased, the δ13C value of the dissolved methane in shallow peat was influenced by the isotopically light methane and approached-61‰. Peat incubation experiments conducted at 15°C in May and June (when the peat reaches its maximum temperature) indicated that an average of 84 ± 9{\%} of the methane production was from acetate and had an average δ13C value of-48.7 ± 5.6‰. Rising acetate concentrations during April-May (approaching 1 mmol L-1(mM)) followed by a rapid decrease in acetate concentrations during May-June reflected the shift toward methane production dominated by acetate fermentation. During this period, dissolved methane in shallow peat at the site returned to heavier values (approximately-5 l{\%}o) similar to that produced in the incubation experiments.",
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Effect of seasonal changes in the pathways of methanogenesis on the δ13C values of pore water methane in a Michigan peatland. / Avery, G. Brooks; Shannon, Robert David; White, Jeffrey R.; Martens, Christophers; Alperin, Marc J.

In: Global Biogeochemical Cycles, Vol. 13, No. 2, 01.06.1999, p. 475-484.

Research output: Contribution to journalArticle

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N2 - The δ13C value of pore water methane produced in a Michigan peatland varied by 11% during the year. This isotopic shift resulted from large seasonal changes in the pathways of methane production. On the basis of mass balance calculations, the δ13C value of methane from CO2 reduction (average =-71.4 ± 1.8%) was depleted in 13C compared to that produced from acetate (-44.4 ± 8.2%o). The dissolved methane at the site remained heavy (approximately-51%o) during most of the year. Tracer experiments using 14C-labeled CO2 indicated that during January 110 ± 25% of the methane was produced by CO2 reduction. Because of low-methane production rates during the winter, this C-depleted methane had only a slight effect on the isotopic composition of the methane pool. In early spring when peat temperatures and methane production rates increased, the δ13C value of the dissolved methane in shallow peat was influenced by the isotopically light methane and approached-61‰. Peat incubation experiments conducted at 15°C in May and June (when the peat reaches its maximum temperature) indicated that an average of 84 ± 9% of the methane production was from acetate and had an average δ13C value of-48.7 ± 5.6‰. Rising acetate concentrations during April-May (approaching 1 mmol L-1(mM)) followed by a rapid decrease in acetate concentrations during May-June reflected the shift toward methane production dominated by acetate fermentation. During this period, dissolved methane in shallow peat at the site returned to heavier values (approximately-5 l%o) similar to that produced in the incubation experiments.

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