Functioning of a French hydroelectric reservoir. Isotopic approach

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 O-18 show evaporation at the water-atmosphere interface. The C-13 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. ((C) Academie des sciences /Elsevier, Paris.).