Transfer of radionuclides and organic matter in the Rhone delta coastal zone studied with large field-deployed mesocosms .

Thébault H., Alliot E. CIESM Workshop Monographs n°19. Metal and radionuclides bioaccumulation in marine organisms – Ancona, 27-30 October 2002 / 43-46.

The bioaccumulation factors and the transfer rates of contaminants between the various components of the aquatic ecosystems have been generally determined in lab experiments with small volume aquaria and sometimes in conditions far from those found in the natural environment. Moreover, the food chains used in those experiments are usually very simplified compared to the complexity of interactions controlling the behavior of contaminants in coastal waters (Santschi, 1988). Therefore, the mesocosms (enclosed meso-scale experimental ecosystem) have become widely used as reliable research tools in aquatic ecology (Brinkman et al., 1994). As the ecological realism of the mesocosms is size-dependant, there is a sound interest for large enclosures (Petersen et al., 1999), deployed in situ to come closer to natural conditions, especially with an undisturbed sediment compartment (Kraufvelin, 1999). But the optimal implementation, including operation easiness for long term studies, need to be tested first for each marine environment. The transfer of some artificial radionuclides between the major compartments of an estuarine Mediterranean ecosystem was studied along with the organic matter balance. The field experiments were conducted to provide controlled and reproducible conditions within a global and holistic experimental concept. This isolated portion of the coastal ecosystem allowed observations on the distribution and the transfer factors in the dissolved phase of the water column, particulate matter, filter-feeding organisms (mussels) and sediment