Assessing the potential of anaerobic oxidation of methane in the terrestrial mud volcanoes, southwestern Taiwan
Date Issued
2008
Date
2008
Author(s)
Chu, Pao-Hsuan
Abstract
Anaerobic oxidation of methane (AOM) has been regarded as the most effective methane sink to attenuate the greenhouse effect caused by methane emission in marine environments. AOM typically occurs at the sulfate-methane interface (SMI) at which syntrophic microbial communities composed of anaerobic methanotrophs and sulfate reducing bacteria consume sulfate percolated from the top seawater and methane produced by either microbial or geological processes underneath. Unraveling whether such a syntrophic relationships would be subject to the variations in the sulfate and methane supply induced by geological processes would benefit to single out the factors governing the methane greenhouse effect on a global scale, and to provide insights to the carbon and sulfur cycling in different environmental settings. Previous studies indicated that terrestrial and marine mud volcanoes in the southwestern Taiwan might bear the intimate origin. While methane concentrations are generally high in both marine and terrestrial mud volcanoes, sulfate supply could vary orders of magnitude. The purpose of this study was to explore (1) whether AOM could be still sustained or even actively act as an important methane sink in southwestern mud volcanoes where sulfate would be a limited factor for AOM; and (2) whether AOM is dependent upon the syntrophic relationships with sulfate reduction or a new syntrophic strategy is developed to accommodate the restricted sulfate supply. This study chose three sites (Chao-Shih-Tan, Shin-Yang-Nih-Hu, and Shiao-Kun-Shih) for sampling of short push-cores (30-50 cm) from which pore water and gas chemistry of depth intervals were analyzed in order to construct a potential geochemical and microbiological model for terrestrial mud volcanoes. The results indicated that both pore water and gas geochemistry varied substantially both in geographic locations and on vertical scales. For geographical locations, pore water in Chao-Shih-Tan possessed highest sulfate (0.5-0.8 mM) but lowest methane (0.1-0.5 mM). In contrast, lower sulfate (<1 mM), and greater methane (up to 20 mM) were observed in Shin-Yang-Nih-Hu, and Shiao-Kun-Shih. Both pore waters in Chun-Lun and Shiao-Kun-Shih were highly saline (generally above 200mM and up to 650 mM Cl-), whereas moderately saline (generally 100-160 mM Cl-) for Shin-Yang-Nih-Hu. Sulfate and methane abundances declined and enhanced at various degrees, respectively, with the increase of depth. The SMI features based on the sulfate and methane variations over depth were observed in all three locations, suggesting the ubiquitous presence of AOM in southwestern mud volcanoes. The depth intervals of the SMI were assigned at depths of 4 to 12 cm in Chun-Lun, of 8-15 cm in Shin-Yang-Nih-Hu, and of 7-12 cm and 25-32 cm in Shiao-Kun-Shih. Despite AOM and sulfate reduction, aerobic methane oxidation, methanogesis and ethanogenesis were also involved in the carbon and sulfur cycling in the southwestern terrestrial mud volcanoes. The syntrophic relationships between AOM and sulfate reduction was primarily driven by the high methane flux produced from the in situ methanogenesis and elevated sulfate abundances generated during the surface evaporation of the erupted muddy fluids.
Subjects
anaerobic oxidation of methane
terrestrial mud volcanoes
SDGs
Type
thesis
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