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| Titel |
Stable isotope and microbial analyses of methane-producing process in a geothermal aquifer associated with the subsurface of the accretionary prism, Japan |
| VerfasserIn |
S. Hattori, H. Kimura, H. Nashimoto, K. Koba, K. Yamada, M. Shimizu, H. Watanabe, M. Yoh, N. Yoshida |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020976
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| Zusammenfassung |
| The sedimentary layer in the southern part of Japan is accretionary prism which includes
enriched organic materials derived from sediment on oceanic plate. There is geothermal
aquifer in which a large amount of methane (CH4) dissolved. Since CH4 is important as a
greenhouse gas and an important natural gas fuel, revealing CH4-producing process in
subsurface environment is required. To understand the process of the CH4 production, we
collected the groundwater from the aquifer of 1,189-1,489 m depth, and analyzed by using
stable isotope and microbial analyses.
16S rRNA gene analysis showed a dominancy of hydrogenotrophic methanogens
in domain Archaea and a dominancy of anaerobic heterotrophes to be known to
produce H2 and CO2 by fermentation process in domain Bacteria. The anaerobic
enrichment cultures with the groundwater amended with organic substrates showed that
CH4 was produced by co-culture between the fermenters and hydrogenotrophic
methanogens. On the other hand, conventional isotopic estimations for the origin
of CH4 using δ13C-CH4 and δD-CH4 as well as δ13C-CH4and molecular ratio
of C1/(C2+C3) indicated that CH4 was derived from thermogenic pathway. The
values of δ13C-CO2, however, had higher values and carbon isotope fractionation
factors between CH4 and CO2(α(CO2-CH4)) were approximately 1.05 to 1.06
indicating the possibility of biogenic CH4 production. Therefore, the origin of CH4
production was estimated as mixing both thermogenic and CO2 reduction from isotopic
data.
Furthermore, we incubated these enriched co-cultures and measure stable carbon isotope
ratios of CH4 and CO2 and stable hydrogen isotope ratios of H2O and CH4. We revealed that
concentration of H2 were kept lower by these co-cultures between fermenters and
hydrogenotrophic methanogens and α(CO2-CH4) values were higher than that of cultures
with the ground water amended with high concentration of H2+ CO2. Hydrogen isotope
fractionation factor between H2O and CH4 by these co-culture increased (αH values
decreased) with increasing H2 concentration. |
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