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

Abstract : 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 km2) is by far the main supplier of sediment to the Mediterranean Sea and its annual solid discharge is largely controlled by ␣ood events. This study investigates the relevance of alternative and original ␣ngerprinting 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 ␣oods. Floods were classi␣ed according to the relative contribution of the main subcatchments (i.e., Oceanic, Cevenol, extensive Mediterranean and gener- alised). Between 2000 and 2012, 221 samples of suspended sediment were collected at the outlet and were shown to be representative of all ␣ood types that occurred during the last decade. Three geogenic radionuclides (i.e., 238U, 232Th and 40K) were used as ␣ngerprints 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 2.106tons, respectively. These results highlight the role of Pre-Alpine tributaries as the main sediment supplier (53%) to the Rhone River during ␣oods. Other ␣ngerprinting approaches based on arti␣cial radionuclide activity ratios (i.e., 137Cs/239 + 240Pu and 238Pu/239 + 240Pu) were tested and provided a way to quantify sediment remobilisation or the relative contributions of the southern tributaries. In the future, ␣n- gerprinting methods based on natural radionuclides should be further applied to catchments with heterogeneous lithologies. Methods based on arti␣cial radionuclides should be further applied to catchments characterised by heterogeneous post-Chernobyl 137Cs deposition or by speci␣c releases of radioactive ef␣uents.
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Article dans une revue
Science of the Total Environment, Elsevier, 2015, 502, pp.122-132. 〈10.1016/j.scitotenv.2014.08.082〉
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Soumis le : vendredi 21 novembre 2014 - 11:23:05
Dernière modification le : jeudi 19 avril 2018 - 14:28:03

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Mathilde Zebracki, Frédérique Eyrolle-Boyer, Olivier Evrard, David Claval, Brice Mourier, et al.. Tracing the origin of suspended sediment in a large Mediterranean river by combining continuous river monitoring and measurement of artificial and natural radionuclides. Science of the Total Environment, Elsevier, 2015, 502, pp.122-132. 〈10.1016/j.scitotenv.2014.08.082〉. 〈hal-01085335〉

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