Christelle Antonelli

Recent morphological channel changes in a deltaic environment. The case of the Rhone River, France

Abstract Channel morphological changes were measured at two sites within the Rhone delta along the main channel of the Rhone River over one century. Results show an average erosion rate of 2.8 mm year−1 during the 20th century and decreasing to

Tracing the origin of suspended sediment in a large Mediterranean river by combining continuous river monitoring and measurement of artificial and natural radionuclides.

Delivery of suspended sediment from large rivers to marine environments has important environmental impacts on coastal zones. In France, the Rhone River (catchment area of 98,000 km(2)) is by far the main supplier of sediment to the Mediterranean Sea and its annual solid discharge is largely controlled by flood events. This study investigates the relevance of alternative and original fingerprinting techniques based on the relative abundances of a series of radionuclides measured routinely at the Rhone River outlet to quantify the relative contribution of sediment supplied by the main tributaries during floods. Floods were classified according to the relative contribution of the main subcatchments (i.e., Oceanic, Cevenol, extensive Mediterranean and generalised). Between 2000 and 2012, 221 samples of suspended sediment were collected at the outlet and were shown to be representative of all flood types that occurred during the last decade. Three geogenic radionuclides (i.e., (238)U, (232)Th and (40)K) were used as fingerprints in a multivariate mixing model in order to estimate the relative contribution of the main subcatchment sources-characterised by different lithologies-in sediment samples collected at the outlet. Results showed that total sediment supply originating from Pre-Alpine, Upstream, and Cevenol sources amounted to 10, 7 and 2.10(6)tons, respectively. These results highlight the role of Pre-Alpine tributaries as the main sediment supplier (53%) to the Rhone River during floods. Other fingerprinting approaches based on artificial radionuclide activity ratios (i.e., (137)Cs/(239+240)Pu and (238)Pu/(239+240)Pu) were tested and provided a way to quantify sediment remobilisation or the relative contributions of the southern tributaries. In the future, fingerprinting methods based on natural radionuclides should be further applied to catchments with heterogeneous lithologies. Methods based on artificial radionuclides should be further applied to catchments characterised by heterogeneous post-Chernobyl (137)Cs deposition or by specific releases of radioactive effluents.

Tritium in river waters from French Mediterranean catchments: Background levels and variability

Tritium background levels in various environmental compartments are deeply needed in particular to assess radiological impact, especially in river systems where most of releases from nuclear facilities are performed. The present study aims to identify the main environmental factors that influence tritium background levels in rivers at the regional scale. 41 samples were collected from 2014 to 2016 along 17 small rivers in the south of France. All were located out of the influence of direct releases from nuclear facilities. Tritiated water (HTO) concentrations measured in water samples ranged from 0.12±0.11 to 0.86±0.15BqL-1 and HTO concentrations in rains were modelled between 2015 and 2016 over the study period referring to time series acquired from 1963 to 2014 at Thonon-les-Bains monitoring station. The results of tritium concentrations in rivers studied present a significant variability and are more than twice lower than forecasted values in rain. Multiple linear regressions allowed identifying that HTO concentration in rains, watershed area and altitude were the main tested parameters that are linked to the variability of HTO concentrations in the studied rivers. Finally, HTO fluxes delivered to the Mediterranean Sea by French coastal rivers out of influence of nuclear releases were estimated. The results highlight that those account for around 1% of HTO exported while 99% are transferred by the nuclearized Rhone River.

Characterisation of naturally occurring radionuclides in the Lower Rhone River (France): preliminary results from suspended solid monitoring

Long term time series acquired in the frame of radioecological monitoring programmes are useful tools for exploring the variability of naturally occurring radionuclide contents. The data set was established in order to investigate the role of discharge, flood type and flood chronicles on such variability within the suspended sediments. Preliminary results show that radionuclide geochemical properties as well as suspended sediment nature and particle residence time may in some particular cases significantly affect the U-Th series nuclide equilibrium.