Origin of suspended particulate matter in a karstic aquifer system: contribution of the microgranulometry.

The study of the river Heurt karst (Upper Normandy) permits us to quantify the origin of particles by use of microgranulometry of different geological formations and waters. At low-water level, 70 % of suspended matter is der ived from the dissolution of chalk and 30 % from the resuspension of clayey -limes. At the end of high-water level, 47 % of the sold constituents deriv e from aeolian loams and 53 % are microflocs, remnant from decantation. Thi s indicates a reservoir perched at the interface of superficial chalk forma tions (Coniacian) in which the major part of dissolution is brought about, generating the majority of the turbidity during high-water level. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.