Frédérique Eyrolle, Olivier Radakovitch, Patrick Raimbault, Sabine Charmasson, Christelle Antonelli, Emmanuelle Ferrand, Dominique Aubert, Guillaume Raccasi, Stéphanie Jacquet, Rodolfo Gurriaran
Abstract
Purpose
Almost 20 nuclear
reactors are situated along the Rhône valley, representing Europe’s
largest concentration of nuclear power plants. The fate of suspended
sediments and natural and artificial particle-bound radionuclides in
relation to extreme hydrological events was assessed at the lower course
of the Rhône River, which provides the main source of water and
sediment inputs to the northwestern Mediterranean Sea.
Materials and methods
We sampled water at a
high frequency over the period 2001–2008 and measured suspended
particulate matter (SPM) loads and particle-bound natural and artificial
radionuclide concentrations at the SORA observatory station in Arles,
France. We monitored various hydrological events (either natural or
anthropogenic origin) and characterize their influence on concentrations
and fluxes.
Results and discussion
The relationship
between SPM concentration and the very wide range of water discharges
did not differ significantly from previous periods, indicating no
significant shift in the average sediment delivery over the last
20 years. Unexpected hydrological events of anthropogenic origin, in
particular those associated with flushing of reservoirs that are
generally not captured by sampling strategies, were recorded and were
shown to transfer significant additional sediment and associated
contaminants towards the marine environment. Concentrations of
anthropogenic radionuclides associated with sediment (i.e., 137Cs, 60Co, 54Mn, 110mAg,
and Pu isotopes) varied over two to three orders of magnitude during
periods of low and moderate flow due to variations in the liquid release
from nuclear facilities. Except for Pu isotopes, the concentrations of
the various particle-bound radionuclides generally showed a decreasing
trend with increasing discharge, revealing the geochemical or
anthropogenic background values, and providing a useful flood
fingerprint for this large fluvial system before its entry into the
marine environment.
Conclusions
Our approach produced
key data on the level and fate of suspended solids and radionuclide
concentrations during flood events occurring in a large river system
that could be contaminated by chronic or accidental radioactive
releases. These results are of fundamental importance for further
interpretations of sediment dynamics at the river mouth.
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