Abstract
This study analyzed cored sediments retrieved from sites distributed across a transect of the Lei-Gong-Hou mud volcanoes in eastern Taiwan to uncover the spatial distributions of biogeochemical processes and community assemblages involved in methane cycling. The profiles of methane concentration and carbon isotopic composition revealed various orders of the predominance of specific methane-related metabolisms along depth. At a site proximal to the bubbling pool, the methanogenic zone was sandwiched by the anaerobic methanotrophic zones. For two sites distributed toward the topographic depression, the methanogenic zone overlaid the anaerobic methanotrophic zone. The predominance of anaerobic methanotrophy at specific depth intervals is supported by the enhanced copy numbers of the ANME-2a 16S rRNA gene and coincides with high dissolved Fe/Mn concentrations and copy numbers of the Desulfuromonas/Pelobacter 16S rRNA gene. Assemblages of 16S rRNA and mcrA genes revealed that methanogenesis was mediated by Methanococcoides and Methanosarcina. pmoA genes and a few 16S rRNA genes related to aerobic methanotrophs were detected in limited numbers of subsurface samples. While dissolved Fe/Mn signifies the presence of anaerobic metabolisms near the surface, the correlations between geochemical characteristics and gene abundances, and the absence of aerobic methanotrophs in top sediments suggest that anaerobic methanotrophy is potentially dependent on iron/manganese reduction and dominates over aerobic methanotrophy for the removal of methane produced in situ or from a deep source. Near-surface methanogenesis contributes to the methane emissions from mud platform. The alternating arrangements of methanogenic and methanotrophic zones at different sites suggest that the interactions between mud deposition, evaporation, oxidation and fluid transport modulate the assemblages of microbial communities and methane cycling in different compartments of terrestrial mud volcanoes.
Highlights
Terrestrial mud volcanoes are ubiquitous in compressional tectonic regimes (Kopf, 2004)
This study extends previous efforts (Chang et al, 2012) to a broader spatial scale by analyzing sediments across a transect of a cone-shaped feature at the Lei-Gong-Hou mud volcanoes (LGHMVs) in eastern Taiwan
The results observed in this study provide an alternative mechanistic explanation that methanogenesis in near-surface environments can account for enhanced methane emissions from the mud platform
Summary
Terrestrial mud volcanoes are ubiquitous in compressional tectonic regimes (Kopf, 2004). Despite focused flows channeling along the fracture network, deeply-sourced gases and fluids percolate through pore space of sediments via diffusion and/or advection (Milkov, 2005; Mazzini et al, 2009). Such pervasive gas transport underneath mud volcanoes enables even greater summed methane emissions from surrounding mud platforms (termed micro- or mini-seepage) when compared with those from main conduits or fractures (termed macro-seepage) (Etiope et al, 2004a,b; Hong et al, 2013). As the methane greenhouse effect is greater than that of CO2 by a factor of ∼25, terrestrial mud volcanoes are considered a potent contributor intensifying climatic fluctuations on contemporary and geological time scales (Etiope et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
