Microbial processes in the deep biosphere of the CO2-dominated active fault zone in NW Bohemia
Microbial Ecology and Applied Microbiology
Final Report Abstract
Microbial processes in the so-called “Deep Biosphere” and their link to geological processes are not well understood. It is hypothesized that in active fault zones, due to an intensified substrate support, microbial processes are significantly accelerated compared to other deep subsurface ecosystems. Therefore, active fault zones could be ‘Hot Spots’ of microbial life in the deep subsurface. The Cheb Basin (CZ) is a shallow Neogene intracontinental basin filled with fluvial and lacustrine sediments (≤ 350 m thick) that has formed at the intersection of the Eger Rift. This area is well studied concerning the seismic activity, sedimentology and fault characteristics which are important prerequisites to understand complex bio-geo interactions in fault zones. The aims of this project were to obtain first insights into the microbial abundance, activity, and community structure in fluid-active CO2 conduits of the Eger Rift zone. In the first part of the project the focus was set on wet mofettes. The study results support the hypothesis that mofettes are either analogs to or rather windows into the deep biosphere. Wet mofettes provide access to deeply buried geo-bio-archives. The described community in surface waters from mofettes of central Europe is in large proportions similar to the deep biosphere of geysers and marine thermal vents, such as black smokers. Mainly the influence of elevated CO2 concentrations coupled with changes of pH as well as varying concentrations of iron shaped the community structures and abundances of specific taxa. To analyze the geo-bio interactions in deep conduit structures the pilot hole HJB-1 was drilled in spring 2016, after extensive predrill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 reservoir was discovered in the underlying sandy clay. A pumping test revealed the presence of saline mineral water (Na-Ca-HCO3-SO4 type) having a temperature of 18.6°C. The drill penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.5 m in Palaeozoic schists. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. The microbial community structure and abundance was analyzed along the whole core sequence and the produced fluids. The fluid contained a higher abundance of bacteria in comparison to the lacustrine Miocene sediments. In particular in sediments considered to be in contact with the ascending CO2 and mineral water, the abundance was increased, which indicates a positive influence of transported electron acceptors such as CO2 and sulfate on microbial life. Accordingly, the abundance of microbes did not show a typical decrease with depth. A clear variation of the microbial communities among different lithological units was revealed which highlights the substantial impact of elevated CO2 concentrations and their associated side effects on microbial processes. The results of laboratory simulation experiments indicate that hydrogen – which is released during seismic activity – can potentially trigger methanogenic activity and thus change the gas composition of emanating fluids. Hydrogen, originating from deep fissured granites may thereby function as an electron donor. 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. The exceptional environmental conditions provoke a decrease in diversity and favor the occurrence of anaerobic, acidophilic taxa, whereby sulfate reduction and methanogenesis become distinct processes. The gained knowledge might be useful regarding geo-engineered systems (e.g., geothermal energy, drinking water reservoirs, and carbon or hydrogen subsurface storage facilities).
Publications
- 2015. Mikrobiologische Prozesse in CO2- Aufstiegskanälen. System Erde 5: 28-33
Alawi, M., T. Nickschick, and H. Kämpf
(See online at https://doi.org/10.2312/GFZ.syserde.05.01.1) - (2016). Earthquake impact on iron isotope signatures recorded in mineral spring water. - Journal of Geophysical Research, 121, 12, p. 8548-8568
Schuessler, J. A., Kämpf, H., Koch, U., Alawi, M.
(See online at https://doi.org/10.1002/2016JB013408) - (2017). Drilling into an active mofette: pilot-hole study of the impact of CO2-rich mantle-derived fluids on the geo– bio interaction in the western Eger Rift (Czech Republic). Sci. Dril. 23, 13–27
Bussert, R., Kämpf, H., Flechsig, C., Hesse, K., Nickschick, T., Liu, Q., Umlauft, J.; Vylita, T.; Wagner, D.; Wonik, T.; Flores, H.E.; Alawi, M.
(See online at https://doi.org/10.5194/sd-23-13-2017) - (2017). Microbiological and geochemical survey of CO2-dominated mofette and mineral waters of the cheb basin, Czech Republic. Front. Microbiol. 8:2446
Krauze, P., Kämpf, H., Horn, F., Liu, Q., Voropaev, A., Wagner, D., Alawi, M.
(See online at https://doi.org/10.3389/fmicb.2017.02446) - (2018). Influence of CO2 Degassing on the Microbial Community in a Dry Mofette Field in Hartoušov, Czech Republic (Western Eger Rift). Front. Microbiol. 9, 2787
Liu, Q., Kämpf, H., Bussert, R., Krauze, P., Horn, F., Nickschick, T., Plessen, B., Wagner, D., Alawi, M.
(See online at https://doi.org/10.3389/fmicb.2018.02787)
