Tracing Mixings and Water-rock Interactions in the Loire River Basin (France): δ18O-δ2H and 87Sr/86Sr

Abstract The Loire River drains more than 1/5 th of the French territory and flows into the Atlantic Ocean through plutonic and volcanic rocks in the upper and lower parts and a large sedimentary basin. Through sampling of the Loire River along its main course and its main tributaries during 2 snapshot campaigns at the basin scale (one during a flood event and the other during the following low flow period), the behavior of the stable and Sr isotopes during water mixing and water/rock interactions at the scale of a large river basin having various lithologies is reported. This study highlighted the complex functioning of the river system and the key issue of the relation between surface and groundwater that must be more investigated, especially regarding water resources management.