Influence of H2 and O2 on sulphate-reducing activity of a subterranean community and the coupled response in redox potential

Abstract

Deep Fennoscandian groundwater is anaerobic, reducing in character and populated by a large diversity of obligate and facultative anaerobic microorganisms. Concentrations of H2 and carbon monoxide are often 0.01-1 μM and of dissolved organic carbon (DOC) and methane 0.01-1 mM. Microbial activity involving these electron and energy donors may help keep deep groundwater anaerobic and reduced. H2 was added in concentrations of 0.1-10 mM to a sulphate-reducing community attached to crushed rock in groundwater under a pressure of 2.0 MPa and in situ geochemical conditions. Experiments reported a threshold concentration of approximately 1 μM H2 at which sulphate reduction ceased, despite the presence of DOC and acetate, suggesting that H2 was needed for sulphate-reducing activity. δ13C values of acetate and DOC data suggested that organic material was degraded to acetate by means of a heterotrophic process. New pressure-resistant micro-sensors for measuring Eh indicated an H2-concentration-dependent decrease in Eh. The investigated community rapidly mitigated the increase in Eh caused by repeated additions of 0.1-0.2 mM pulses of O2 as long as H2 was available. The results imply that sulphate reduction to sulphide with H2 may dominate sulphate-rich groundwater, which may have implications for metallic underground constructions. © 2012 Federation of European Microbiological Societies.