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

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 0.011 mu M and of dissolved organic carbon (DOC) and methane 0.011 mM. Microbial activity involving these electron and energy donors may help keep deep groundwater anaerobic and reduced. H2 was added in concentrations of 0.110 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 mu M H2 at which sulphate reduction ceased, despite the presence of DOC and acetate, suggesting that H2 was needed for sulphate-reducing activity. d13C 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 0.10.2 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.