Abstract

The Cheb Basin (CZ) is a shallow Neogene intracontinental basin filled with fluvial and lacustrine sediments that is located in the western part of the Eger Rift. The basin is situated in a seismically active area and is characterized by diffuse degassing of mantle-derived CO2 in mofette fields. The Hartoušov mofette field shows a daily CO2 flux of 23–97 tons of CO2 released over an area of 0.35 km2 and a soil gas concentration of up to 100% CO2. The present study aims to explore the geo–bio interactions provoked by the influence of elevated CO2 concentrations on the geochemistry and microbial community of soils and sediments. To sample the strata, two 3-m cores were recovered. One core stems from the center of the degassing structure, whereas the other core was taken 8 m from the ENE and served as an undisturbed reference site. The sites were compared regarding their geochemical features, microbial abundances, and microbial community structures. The mofette site is characterized by a low pH and high TOC/sulfate contents. Striking differences in the microbial community highlight the substantial impact of elevated CO2 concentrations and their associated side effects on microbial processes. The abundance of microbes did not show a typical decrease with depth, indicating that the uprising CO2-rich fluid provides sufficient substrate for chemolithoautotrophic anaerobic microorganisms. Illumina MiSeq sequencing of the 16S rRNA genes and multivariate statistics reveals that the pH strongly influences microbial composition and explains around 38.7% of the variance at the mofette site and 22.4% of the variance between the mofette site and the undisturbed reference site. Accordingly, acidophilic microorganisms (e.g., OTUs assigned to Acidobacteriaceae and Acidithiobacillus) displayed a much higher relative abundance at the mofette site than at the reference site. The microbial community at the mofette site is characterized by a high relative abundance of methanogens and taxa involved in sulfur cycling. The present study provides intriguing insights into microbial life and geo–bio interactions in an active seismic region dominated by emanating mantle-derived CO2-rich fluids, and thereby builds the basis for further studies, e.g., focusing on the functional repertoire of the communities. However, it remains open if the observed patterns can be generalized for different time-points or sites.

Highlights

  • Due to magmatic activity beneath the Cheb Basin, large-scale degassing of mantle-derived CO2 (>99%) occurs

  • The study site is located in the Cheb Basin (NW Bohemia, Czechia), a shallow Neogene intracontinental basin filled with fluvial and lacustrine sediments (≤350 m thick; Figure 1A)

  • Our study of a dry CO2 degassing mofette in Hartoušov, NW Bohemia, as central part of a CO2 conduit deepens the knowledge of geo–bio interactions in extreme environments with elevated CO2 concentrations

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Summary

Introduction

Due to magmatic activity beneath the Cheb Basin, large-scale degassing of mantle-derived CO2 (>99%) occurs. The diffuse cold gas emanations at the surface (diffuse degassing structures, DDS) can be distinguished as dry and wet mofettes (Kämpf et al, 2013). Mofettes provide insights into life under elevated CO2 concentrations, low pH, and anoxic conditions comparable to the Earth’s ancient atmosphere (Emiliani, 1992; Raven, 1995; Young et al, 2012). Mofettes are used as model ecosystems for studying the response of soil microorganisms to a potential CO2 leakage of underground carbon capture and storage systems (Krüger et al, 2009, 2011; Frerichs et al, 2013; Morales and Holben, 2013). As shown by several studies, these direct influences of elevated CO2 concentrations on the environment are affecting the mofette biota and its biological matter cycling

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