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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., Cs, Co, Mn, Ag, 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. [ABSTRACT FROM AUTHOR]

To obtain a comprehensive picture of the spatial distribution of atmospheric phosphorus (P) speciation in the Mediterranean Sea, deposition samples were collected from the eastern (E) and north-western (NW) Mediterranean and analyzed for both organic and inorganic P forms. Dissolved P, especially in organic form, is dominant during the wet season, while higher insoluble P fluxes are recorded during the dry period, mainly due to dust outbreaks. Wet deposition has a significant contribution to the atmospheric phosphorus flux; over the NW Mediterranean accounting for 80% of the total dissolved phosphorus (TDP). The seven-year average TDP flux during the wet season in the NW basin, of 1.78 mmol m −2 y −1 , is almost double that of the two-year average in the eastern Mediterranean. The difference is attributed mainly to the precipitation height being 2–3 times higher in the NW Mediterranean compared to the East. Dissolved organic phosphorus (DOP) is the dominant P fraction in both wet and dry deposition samples, presenting similar fluxes (1.16 and 0.94 mmol m −2 y −1 , in the eastern and north-western basins respectively). Finally, assuming that all TDP is bioavailable, atmospheric deposition of TDP could account for up to 38% of new production in the eastern Mediterranean, while during oligotrophic periods of the NW Mediterranean it could increase the new production by 14%. [ABSTRACT FROM AUTHOR]