Laboratory simulation of an oxidizing perturbation in a deep granite environment

• Published in: Geochimica et cosmochimica acta 2002-07, Vol.66 (14), p.2583-2601
• Main Authors: Trotignon, Laurent, Michaud, Valrie, Lartigue, Jean-Eric, Ambrosi, Jean-Paul, Eisenlohr, Laurent, Griffault, Lise, de Combarieu, Michel, Daumas, Sylvie
• Format: Article
• Language: English
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(02)00851-7

An experiment designed to study oxidizing perturbations in deep crystalline rock, a potential host for nuclear waste disposal, was conducted. This experiment simulated a fracture surface in contact with circulating groundwater, in which dissolved oxygen was injected periodically. Major physicochemical and biological parameters were monitored during this 1-yr experiment. Modeling of the results indicates that the kinetics of oxygen uptake may be represented by a simple steady-state rate law combining enzymatic catalysis (Monod) and a first-order rate law. Combined chemical and biological data demonstrate the coupling of organic/inorganic processes during the uptake of dissolved oxygen and the progressive return to reducing conditions. Timescales for these stages are discussed. Experimental results also suggest that iron-reducing bacteria, which are robust and well-adapted microorganisms, play a key role in these interfacial processes. These results show that an operational definition of the “redox buffering capacity” in a granitic medium cannot ignore the effect of bacteria and therefore the controls on bacterial substrates (organic carbon, H 2, CH 4, CO 2).