Influence of the Gironde estuary outputs on cadmium concentrations in the coastal waters: consequences on the Marennes-Oleron bay (France)

The Gironde, an estuary in Southwestern France, has been highly contaminate d by cadmium for many years, and the results of the French mussel watch sug gest that this contamination is not restricted to the estuary, but could be responsible for relatively high levels of Cd in the oysters from the Maren nes-Oleron bay located nearby. This hypothesis has been evaluated through t hree cruises carried out in the Gironde estuary and plume, the Marennes-Ole ron bay, and the Charente estuary, a river of minor importance that influen ces directly this bay. The field results from the Pertuis cruise (May 1991) and two others conducted in January and December of the same year show tha t the Gironde is an important source of dissolved cadmium for the bordering continental shelf (11 t year(-1)), while the Charente inputs are far lower (60 kg year(-1)). Dissolved Cd concentrations on the shelf vary according to the salinity, ranging from 0.76 nmol L-1 close to the Gironde to 0.15 nm ol L-1 far from the shore. The field data as well as simulations from a 3D hydrodynamic model show that the Gironde plume reaches the Antioche Straits north of the Marennes-Oleron bay, and that the Charente plume is diluted i n the bay by marine waters strongly influenced by the Gironde. This study c onfirms that the Gironde estuary is an important source of cadmium for the Marennes-Oleron bay. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et me dicales Elsevier SAS.