The global influence of the hydrogen isotope composition of water on that of bacteriogenic methane from shallow freshwater environments

Journal Article · Sun Aug 01 04:00:00 EDT 1999 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(99)00192-1· OSTI ID:687717

Waldron, S; Fallick, A E ^[1]; Lansdown, J M ^[2]; Scott, E M; Hall, A J ^[3]

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1. Scottish Universities Research and Reactor Centre, East Kilbride (United Kingdom)
2. Univ. of Washington, Seattle, WA (United States). School of Oceanography
3. Univ. of Glasgow (United Kingdom)

The authors propose that the hydrogen isotope composition of recently produced microbial methane, {delta}D(CH{sub 4}), in sulfate-poor, shallow freshwater environments, is directly related to the hydrogen isotopic composition of the system water {delta}D(H{sub 2}O). As {delta}D(H{sub 2}O) varies globally, systematic differences in {delta}D(CH{sub 4}) as a function of {delta}D(H{sub 2}O) should be observed. From available mean paired measurements from 46 sites, the relationship for {delta}D(CH{sub 4}) and {delta}D(H{sub 2}O) in the natural environment can be defined as {delta}D(CH{sub 4}) = 0.675{delta}D(H{sub 2}O) {minus}284{per_thousand} (p < 0.0001). This relationship is statistically distinct from that generated by considering three separate laboratory-based anaerobic inoculations that contain similar methanogenic communities to the natural freshwater samples and therefore, are likely to produce methane by similar metabolic pathways: {delta}D(CH{sub 4}) = 0.444{delta}D(H{sub 2}O) {minus}321{per_thousand} (p < 0.0001). The authors suggest that the relationship arising from the laboratory incubations defines the {delta}D(CH{sub 4}) of methane produced at source in shallow freshwater environments. They can approximate that 50% of the variation in natural {delta}D(CH{sub 4}) samples can be explained by {delta}D(H{sub 2}O), with isotopic fractionation postproduction, or mixing with gas already fractionated likely responsible for most of the noise in the natural system and difference of the natural sample relationship to the laboratory relationship. Methanogenic pathway may also influence {delta}D(CH{sub 4}), but the foundations for this hypothesis need to be reconsidered, and field and laboratory data exist that do not support it. The relationships presented here describe {delta}D of methane from only shallow (subsurface) freshwater environments; paired {delta}D(CH{sub 4})-{delta}D(H{sub 2}O) values from other environments (e.g., marine, glacial drift) suggest that a different relationship is needed to describe the influence of {delta}D(H{sub 2}O) on {delta}D(CH{sub 4}).

• OSTI ID: 687717
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 15 Vol. 63; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AQUATIC ECOSYSTEMS
BIOSYNTHESIS
FRESH WATER
HYDROGEN ISOTOPES
ISOTOPE RATIO
METHANE