Offre de stage de M2 : Human impact on a natural system: the case of Manganèse oxides at the Roselend Nat. Lab.

Offre de stage de M2 : Human impact on a natural system: the case of Manganèse oxides at the Roselend Nat. Lab.

Une proposition de stage de M2 (ou une année de césure) à l’Université de Grenoble avec Laurent Charlet (ISTerre) et Éric Pili (CEA, Laboratoire Naturel de Roselend), sur la Reconstitution et les conséquences de l’anthropisation d’un système naturel : cas des oxydes de manganèse au Laboratoire Naturel de Roselend.

The Roselend Natural Laboratory (French Alps) is a research facility dedicated to the study of transfers in the environment. Among many activities, it allows the monitoring of water quality in a massif of crystalline rocks (fractured porous medium), particularly from water inflows in a tunnel located 55 m below an abandoned quarry.

Over the past 15 years, the spreading of cattle manure in the quarry has profoundly modified the chemistry of infiltration water. In particular, the high chemical and biological oxygen demands seem to have deprived the water of its oxygen, turning unstable the manganese oxides naturally occurring in the underlying rocks. Manganese thus put in solution infiltrates through the rocks towards the tunnel, where the presence of oxygen in the atmosphere induces its precipitation in the form of oxides. Large quantities of manganese oxides, and possibly other minerals, were deposited on the tunnel walls and possibly within the fracture network and inside the porous matrix in the vicinity of the tunnel, likely altering the local permeability of the system.

The proposed research project aims to reconstruct the scenario of this irreversible change in this natural environment, from a qualitative and quantitative point of view and to estimate its consequences over the medium and long terms. The physico‐chemical properties of the water will be determined on samples taken in the field, both on the infiltration side (quarry) and on the percolation side (tunnel). The oxide precipitates in the tunnel will be sampled and analyzed to identify the phases. Using rock cores drilled in the quarry and in the tunnel, dissolution and precipitation profiles will be investigated. This will determine how far the permeability and porosity of the rocks, on both the quarry and tunnel sides, are affected by the transfer of manganese. The quantities of transferred material will be estimated. The possibility that other chemical compounds (including arsenic) may be similarly affected will be discussed and the consequences considered.

The student will carry out sampling (water, soil and rock) and physico‐chemical measurements in the field, water characterization by ion chromatography and ICP‐OES in the laboratory as well as solid characterization by SEM and X‐ray fluorescence.

This Master 2 research internship will take place in the Geochemistry Team (ISTerre, Grenoble University), under the direction of Laurent Charlet (ISTerre, laurent.charlet@univ‐grenoble‐ ) and the co‐supervision of Éric Pili (CEA, Laboratoire Naturel de Roselend,