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| Titel |
Microbial communities imposed by different geochemical contexts in Sicilian mud volcanoes |
| VerfasserIn |
Pei-Ling Wang, Yi-Ping Chiu, Li-Hung Lin, Francesco Italiano |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130544
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| Publikation (Nr.) |
 EGU/EGU2016-10814.pdf |
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| Zusammenfassung |
| Mud volcanoes and seeps are prominent surface manifestation of fluid channels
connected to fluid/gas reservoirs in deep subsurface environments. While methane and
carbon dioxide constitute the main components of exsolved gases, the discharge of
these gases into the atmosphere have been estimated to exert profound effects on
greenhouse over contemporary and geological time scales. How microbial processes and
what community compositions imposed by different geochemical contexts near
surface regulate the exact quantity of gas emission remain poorly constrained. In this
study, porewater, gas and sediment geochemistry, and 16S rRNA genes for samples
collected from mud volcanoes in Sicily of Italy were analyzed to investigate the
changes of methane cycling and compositions of methanotrophic populations in
response to different methane/CO2 ratios and other geochemical characteristics in
gas bubbling environments. The analyses yielded contrast patterns of solute and
gas geochemistry, and gene assemblages and abundances between sites related
to different tectonic regimes. For sites located at the southern flank of Mt. Etna,
methane and other hydrocarbons were low (less than tens of μM) in concentrations,
whereas fluids were more saline than seawater and enriched with various solutes.
No apparent methane consumption could be identified from geochemical profiles.
Cell abundances were low, varying between 104 – 106 cells g−1 with anaerobic
methanotrophs being generally less than 104 cells g−1. Communities were primarily
composed of Halobacteriales, Gamma-Proteobacteria, Defferibacteres, Chloroflexi, and
Delta-Proteobacteria. The dominant OTUs were related to heterotrophic halophiles, and
sulfide oxidizers. While a fraction of sequences related to aerobic methanotrophs
were detected, anaerobic methanotrophs and methanogens were rarely present.
In contrast, methane and other hydrocarbons were high (generally more than 0.4
mM) at sites located within accretionary wedge. Fluids were relatively depleted in
solutes (with chloride concentrations ranging about 40% of seawater). Transition
of methane abundances indicative of methane consumption could be equivocally
identified. Cell abundances were high, varying between 108 – 109 cells g−1 with
anaerobic methanotrophs ranging around 107 cells g−1. Communities were primarily
composed of Halobacteriales, ANME, Delta-Proteobacteria, Bacteroidetes, and
Chloroflexi. The dominant OTUs were related to uncultured DHVEG-6, ANME-2,
sulfate reducers and S/Fe reducers. A small fraction of sequences related to aerobic
methanotrophs and methanogens were recovered from samples near surface and at depth,
respectively. Overall, our results combined with previous studies conducted elsewhere
demonstrate that anaerobic methanotrophy and methanogenesis were prevalent in
terrestrial mud volcanoes characterized by low salinity and high methane. Their in situ
activities and interactions with other metabolisms would be vital in determining the
quantity of methane produced within sediments and released into the atmosphere.
Moreover, aerobic heterotrophy and sulfur oxidation dominated over other metabolisms
in mud volcanoes fed with fluids potentially circulating through evaporites and
low-methane volcanic gases. The effectiveness of biological methane filtration is therefore
strongly controlled by geochemical contexts imposed by geological frameworks. |
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