THE INVESTIGATIONS ON THE TRANSFER OF ARTIFICIAL RADIONUCLIDES OF THE MEDITERRANEAN RHONE DELTA COME UNDER THE RADIATION PROTECTION PROGRAMME OF THE EUROPEAN COMMUNITIES. THEY CONSTITUTE ONE OF THE FACETS OF THE EROS-2000 PROJECT (EUROPEAN RIVER OCEAN SYSTEM). IT SUFFICES TO RECALL THE GENERAL OBJECTIVE TO STUDYING THE SOURCES, CYCLES AND BEHAVIOUR OF ORGANIC AND INORGANIC POLLUTANTS AND RADIONUCLIDES IN THE EUROPEAN COASTAL ENVIRONMENT, THE MEDITERRANEAN NORTH OCCIDENTAL BASIN BEING THE OBSERVATION ZONE CHOOSEN FOR THE 1987-1989 PERIOD.
THE PRESENT PROPOSAL AIMS AT SPECIFYING THE ORIGINS OF THE SEDIMENT PARTICLES (NATURAL/ANTHROPIC, MARINE/CONTINENTAL) THEIR TRANSFER MECHANISMS TO THE BOUNDARIES OF THE BASIN AND THE ASSOCIATED SEDIMENTATION LEVELS.
The artificial radionuclides discharged to the Rhone river by various nuclear power and reprocessing plants have been used as tracers to determine the transfer of suspended matter from the Rhone Delta to the Gulf of Lion in the Mediterranean Sea.
The discharge of particulate artifical radionuclides in characterized by alternating periods of low flux or retention separated by strong pulse like inputs.
The fractionation of selected radionuclides between the dissolved and particulate phases was studied. Fresh water fast distribution coefficients (FDCs) of zinc and cadmium were related to suspended matter surface properties. The caesium FDC was totally in opposition. In the brackish part of the system, FDCs were lower than in fresh water, by a factor of 60 for caesium, 25 for cadmium, about 10 for manganese and zinc. In most cases, the observed decreases of FDCs were in agreement with laboratory sorption results, but in some instances the observed behaviour was unexpected. The strong correlation between cobalt and manganese FDCs previously noted was not confirmed.
THE FLOW OF THE OCEAN DRAGGED ALONG BY THE BIG RIVERS IS DISTRIBUTED BETWEEN THE SEDIMENTATION IN THE PROXIMITY OF THE RIVER MOUTHS AND THE TRANSIT BY THE DIVERS TURBID FORMATIONS. THE RELATIVELY RECENT DEVELOPMENT OF THE APPLICATION OF TELEDETECTION HAS ALLOWED TO CHARACTERISE IN A SYNOPTIC WAY THE SUPERFICIAL TURBID PLUMES SPREADING OVER THE SEA OFF THE BIG RIVERS. THIS ELEGANT BRINGING TO EVIDENCE OF THE DISPERSION OF THE CONTINENTAL DETRITAL DEPOSITS HAS SOMETIMES TAKEN PRECEDENCE OVER THE STUDY OF THE PROFOUND TURBID FORMATIONS (NEPHELOID).
THE EXISTENCE OF NEPHELOID SUSPENSIONS IN THE ATLANTIC AND THEIR IMPORTANCE WITH RESPECT TO THE LARGE SCALE SEDIMENTATION HAS NEVERTHELESS BEEN RECOGNIZED FOR LONG BY THE PIONEERS OF THE OCEANOGRAPHY AS WELL AS IN THE MEDITERRANEAN WHERE THEY REPRESENT A PERMANENT SEDIMENTATION PHENOMENON.
THE OBSERVATIONS FORESEEN TO BE MADE IN THE VICINITY OF THE RHONE DELTA AND IN THE ADJACENT MARINE AREA CORRESPOND VERY PARTICULARLY TO FOLLOWING AIMS:
1. TO DETERMINE THE FORMATION OF PARTICLES IN THE NEPHOLOID SYSTEM
2. TO STUDY THE DEVELOPMENT OF PARTICLES IN THE NEPHOLOID SYSTEM
- EXTENSION IN THE SEA AND GRAULOMETRIC STRUCTURE OF THE NEPHELOID LAYER
- LEVEL OF MIXTURE OF THE RHONE PARTICLES WITH THE LATERAL SOURCES
USE OF LON-LIVED RADIOELEMENTS : PU 238/PU 239
- ESTIMATION OF THE TRANSIT TIME OF THE PARTICLES (SHORT-LIVED RADIOELEMENTS : CO-58/CO-60, RU-106)
- EXCHANGES WITH OTHER TURBID BODIES: SURFACE PLUME AND DEPOSITED SEDIMENTS (COSMOGENIC RADIOELEMENTS : BE-7)
3. TO CALCULATE THE IMPACT OF THESE DEPOSITION PROCESSES ON THE FLOW OF RADIOELEMENTS TO THE MEDITERRANEAN.