Evolution of the Soil Cover of a Limestone Plateau as a Consequence of Climate Cooling : a Predictive Approach.
Sophie Maillant1, Guillaume Echevarria1, Michel Gury1, Brigitte Van Vliet Lanoe2, Elisabeth Leclerc-Cessac3, and Jean-Louis Morel1. (1) Laboratoire Sols et Environnement UMR 1120 INPL-INRA, 2 av de la Foret de Haye, Vandoeuvre-lès-Nancy,, 54500, France, (2) Processus et Bilans des Domaines Sédimentaires, UMR 8110 CNRS, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, 59655, France, (3) Andra, Direction Scientifique, Service Transferts, 1-7 rue Jean Monnet, Châtenay-Malabry, 92298, France
A safety assessment for an underground radioactive disposal in the deep rocks of a limestone plateau is being conducted in France by Andra (Andra, 2005). Within the next five hundred thousands years, the Earth climate would turn from interglacial into glacial and the limestone plateau considered would be under periglacial conditions. Therefore, when assessing the behaviour of radionuclides in soils in the considered area it is necessary to take into account the changes induced in the soil by the periglacial conditions. Here, we present a method for the assessment of these pedological changes. The method relies on the study of analogous soils, sampled in regions similar to the initial limestone plateau regarding the geochemical (calcareous) and topographical contexts but undergoing a cold climate which mimics the future periglacial conditions (steppe-tundra or boreal forest biomes). We have added to the cold and dry climatic series a cold and humid biome (montane strata). The analogous soils sampled have developed under boreal forest, cold steppe and subalpine conditions from limestone or calcareous parent materials. The observed soils were eutric Leptosols under boreal forest, and Chernozems under cold steppe. In the montane strata, the leaching of carbonates was strong enough to allow a diversification of soil genesis: from humic Leptosols to dystric Luvisols. This study has confirmed that the biggest differences between soils were observed between the humid and cold climate (montane) on one side and the dry and cold (cold steppe and boreal) on the other. Evolution scenarios constructed from these results indicated that the periglacial conditions would probably favour the persistence of soils still similar to the present ones in the reference region, especially during the boreal stage. However these soils would display higher OM content. In this biome, soils would be mainly rendzic Leptosols and eutric (or calcaric) Cambisols as presently. In the steppe-tundra biome, a pergelisol would favour hydromorphy and/or mechanical disturbance in most soils (stagnic turbic Cryosols). In both biomes, hydromorphic soils, developped on marly material could display very high OM content (fen). Maps summarising these scenarios have been edited for each biome.