Groundwater dependence of acidic valley mires in basement regions: field and modelling evidence from the Massif Central (France)’

The Massif Central is one of the areas with the highest density of mires in Metropolitan France, a large number of which are acidic valley mires located at the bottom of etch-basins on crystalline hard rocks. Many of these wetlands have been designated as Special Areas of Conservation under the EU Habitats Directive, yet very little is known on their hydrological functioning. Recent work has, however, shown that many basement regions support continuous stratiform composite aquifers due to the presence of a deep densely fissured layer between the saprolite and the unweathered bedrock.