HR: 0800h
AN: NS51A-03    [Abstracts]
TI: Laboratory Measurements of Self-Potential (SP) During Biologically-Induced Precipitation of Calcite
AU: * Naudet, V
EM: v.naudet@cdga.u-bordeaux1.fr
AF: Centre de Developpement en Geosciences Appliquee, Universite Bordeaux 1, batiment 18, Avenue des Facultes, 33405, Talence, France
AU: Maineult, A
EM: maineult@jussieu.ipgp.fr
AF: Equipe de Geomateriaux en Environnement, Institut de Physique du Globe de Paris et Universite Paris-Diderot, CNRS, 4 place Jussieu, 75005, Paris, France
AU: Menez, B
EM: menez@jussieu.ipgp.fr
AF: Equipe Geobiosphere Actuelle et Primitive, Institut de Physique du Globe de Paris et Universite Paris-Diderot, CNRS, 4 place Jussieu, 75005, Paris, France
AU: Zamora, M
EM: zamora@jussieu.ipgp.fr
AF: Equipe de Geomateriaux en Environnement, Institut de Physique du Globe de Paris et Universite Paris-Diderot, CNRS, 4 place Jussieu, 75005, Paris, France
AB: Self-potential (or natural electrical field) data often provide complementary information for hydrological and environmental applications. Particularly, this method can be used to detect and quantify the variations of fluid flow or chemistry, as SP field results mainly from pressure and concentration gradients. Recent laboratory and field works have demonstrated that bacterial activity can also impact on this natural electrical field, even though the chemical and/or physical processes involved are still not well understood. It seems that direct transfer of electrons through biofilms triggers an electrical signal. Moreover, in an indirect way, the bacterial activity affects the fluid composition and the solute concentrations, as well as the properties of the surface of the mineral matrix, and thus changes the SP response. In order to provide some insights into the link between bacterial activity, chemistry and geophysics, we performed some laboratory experiments in sand-boxes. In particular, we studied the chemical and electrical response to the hydrolysis of urea by Bacillus pasteurii in presence of calcium. Schematically, bacteria were confined in the centre of the sand-box to avoid chemotactic migration. The sand was fully saturated with a nutrient solution containing urea (5 g/L), NaCl (8 g/L) and CaCl2-2(H2O) (2.8 g/L). The SP field was recorded continuously using small unpolarizable electrodes placed inside the sand. The chemical evolution of the solution at different distances from the centre of the box was daily analyzed. We report our preliminary results. The chemical evolution with time evidences at least two phases. First, a strong ammonium production, associated with the biodegradation of the urea, and a concomitant decrease of calcium ion content, due to the precipitation of calcite. Then, the biodegradation rate decreases or even goes to zero, while the by-products diffuse from the centre of the sand-box toward its borders. The SP variations are correlated with these different phases of biological activity.
DE: 0419 Biomineralization
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0614 Biological effects
DE: 1835 Hydrogeophysics
DE: 5109 Magnetic and electrical properties (0925)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly