Microbial methane cycling in the Lei-Gong-Huo mud volcano of eastern Taiwan.
Date Issued
2011
Date
2011
Author(s)
Chang, Yung-Hsin
Abstract
Mud volcanoes and cold seeps are important geological features that facilitate the export of microbial and/or thermogenic hydrocarbons from deep sources to the overlying seawater and/or atmosphere. Understanding how microbial communities are regulated in terrestrial mud volcanoes would facilitate to unravel the carbon cycles linking deep and shallow reservoirs. The objective of this study was to characterize microbial communities associated with bubbling fluid and sediments along depth in two sites of the Lei-Gong-Huo mud volcano in eastern Taiwan. These sites were chosen (BF: bubbling fluid; site A: 0.34 meter from venting center; site B: 1.53 meter from venting center) in order to investigate how fluid flux would shape the community structures.
Site comparisons revealed that anaerobic, halophillic, salt-tolerated microorganisms were prevalent in both sites. Iron to methane transition occurred at depths of 5-9 cm and 29 cm in site A where archaeal populations were dominated by ANME-2a. The abundances of ANME-2a were positively correlated with those of Desulfomonas/Pelobacter sp., suggesting that anaerobic methanotrophy is coupled to the metal reduction. Methanogenesis primarily catalyzed by methylotrophic methanogens were actived at 9-27 cm depths of site A and shallow intervals of site B. Bacterial communities were highly diverse and composed of different assemblages. Dominant bacterial members switched from Desulfuromonas, Pelobacter, Marinobacter and uncultured Bacteroidetes-related microorganisms in site A to Thiohalophilus and uncultured Bacteroidetes-related microorganisms in site B.
The molecular evidence combined with geochemical characteristics revealed that the interplay between the upwelling, hydrocarbon-rich fluids, and downward atmospheric oxygen is essential to regulate community assemblages and functional expressions in mud volcanoes. Methane emission in the mud volcanoes was controlled by microbial processes. Near the venting site, methane is consumed by iron-dependent anaerobic oxidation of methane. Far from the venting site, methane produced from methanogen was directly realeased to atmosphere.
Subjects
mud volcano
microbial methane cycling
Type
thesis
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