Fonctionnement d'une retenue hydroélectrique française. Approche isotopique

In order to better understand the hydric behaviour of the Bort-les-Orgues reservoir, physico-chemical studies, as well as isotopic studies were carried out in 1996 and 1997. The physical results show that the lake is monomictic, with thermic stratification from June to September–October. The high values of pH in the surface water during summer reveal an active development of biological production starting in June. Isotopic values of 18O show evaporation at the water-atmosphere interface. The 13C of the dissolved total inorganic carbon is governed both by atmospheric exchange and biologic activity. Information about the internal dynamics of the reservoir such as a water current, an upstream water column renewal (by ‘piston effect’), and a downstream sediment resuspension can thus be obtained.