The influence of methane oxidation on the stable isotopic composition of methane emitted from Florida swamp forests

doi:10.1016/0016-7037(94)90341-7

Geochimica et Cosmochimica Acta

Volume 58, Issue 20, October 1994, Pages 4377-4388

https://doi.org/10.1016/0016-7037(94)90341-7 Get rights and content

Abstract

This study reports the first measurements of the δ¹³C of CH₄ emitted from seasonally flooded swamp forests in the southeastern United States. The seasonally averaged δ¹³C of CH₄ emitted from a north Florida swamp forest located in the St. Marks National Wildlife Refuge was −52.7 ± 6.11%. (error is ± one standard deviation throughout, n = 28), a value ¹³C-enriched, relative to typical wetland emissions. In an Everglades cypress dome, the average δ¹³C of emitted CH₄ was −52.5 ± 6.7%.(n = 3). Consistent with attenuation of CH₄ emission by CH₄ oxidation in these environments, CH₄ emitted via diffusion from the St. Marks swamp forest was enriched in ¹³C by 6.4 ± 5.8%. (n = 28) and D by 57 ± 36%. (n = 6) relative to sedimentary CH₄. Methane emitted from the cypress dome had also been altered by oxidation, as it was enriched in ¹³C by 12.1 ± 4.3%. relative to sedimentary CH₄. Emission experiments, performed in situ with inhibitors of aerobic CH₄ oxidizing bacteria, were used to calculate the fractionation factors (α) for stable carbon and hydrogen isotopes of CH₄ undergoing transport and oxidation. Values ranged from 1.003 to 1.021 and 1.050 to 1.129, respectively. The best estimates for carbon and hydrogen α values were 1.020 and 1.068, respectively. The δ values of produced (sedimentary) CH₄ were relatively constant in the St. Marks subtropical swamp forest. Additionally, because the transport of CH₄ to the atmosphere was dominated by molecular diffusion, variations in the magnitude of CH₄ oxidation appeared to be the primary factor controlling the δ values of emitted CH₄. This contrasts with systems dominated by bubble ebullition, where variations in CH₄ production mechanisms have been hypothesized to be the primary factor controlling the δ values of emitted CH₄.

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The influence of methane oxidation on the stable isotopic composition of methane emitted from Florida swamp forests

Abstract

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

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