Hydrogeochemical stratification and vertical flows in the Beauce calcareous aquifer (France): a human-influenced system with strong spatial and temporal variability

Vertical profiles of temperatures and flow velocities, as well as water sam ples taken at different depths, reveal a hydrogeochemical stratification of the Beauce calcareous aquifer. This stratification, which is particularly well marked for the NO3- and Cl- profiles, is related to the development of intensive agriculture. It presents a strong variability: (i) in space beca use of the aquifer's multi-layered structure and the presence of reducing l evels, (ii) and in time due to the existence in the boreholes of a vertical flow, the direction of which depends on the periodic exploitation of the a quifer. ((C) 1999 Academie des sciences / Editions scientifiques et medical es Elsevier SAS.).