Depositional environments and historical contamination as a framework to reconstruct fluvial sedimentary evolution

Sophia Vauclin (1) , Brice Mourier (1) , André-Marie Dendievel , Nicolas Noclin (1) , Hervé Piégay (2) , Philippe Marchand (3) , Anaïs Vénisseau (3, 4) , Anne de Vismes (5) , Irène Lefèvre (6, 7) , Thierry Winiarski

1 ENTPE - École Nationale des Travaux Publics de l'État
2 ENS de Lyon - École normale supérieure de Lyon
3 LABERCA - Laboratoire d'étude des Résidus et Contaminants dans les Aliments
4 ONIRIS - École nationale vétérinaire, agroalimentaire et de l'alimentation Nantes-Atlantique
5 IRSN - Institut de Radioprotection et de Sûreté Nucléaire
6 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
7 GEDI - Géochimie Des Impacts

In this study, we explore the variability of sedimentation conditions (e.g., grain-size, accumulation rate, contamination) according to fluvial depositional environments. Indeed, sediment cores are commonly used as archives of natural and anthropogenic activities in hydrosystems, but their interpretation is often complex, especially in a fluvial context where many factors may affect the quality, continuity, and resolution of the record. It is therefore critical to thoroughly understand the nature and dynamics of an environment in which a sediment core is sampled to be able to interpret it. To that end, four depositional environments from a bypassed reach of the Rhône River were comparatively investigated through geophysics in order to assess the range of sedimentation conditions: a floodplain, a semi-active secondary channel, an active secondary channel, and a dam reservoir. Sediment cores were retrieved from each environment and thoroughly characterised (e.g., grain-size, Total Organic Carbon, organic contaminants). Robust age-depth models were elaborated for each core based on 137Cs, 210Pbex, and Persistent Organic Pollutants (POPs) trends. The results show that each depositional environment recorded a different time-period, and therefore different contamination levels and trends. In particular, a shift from polychlorinated biphenyls (PCBs) to polybrominated diphenyl ethers (PBDEs) as the predominant POP in the sediments can be observed, the tipping point being set in the 1970s. Two types of infrastructure-induced legacy sediments related to two periods of river engineering in the reach were also identified using grain-size analysis. The combination of geophysical methods (Ground Penetrating Radar) and sediment cores is therefore confirmed as a relevant methodology that should be promoted in fluvial contexts in order to reconstruct the sedimentary evolution of fluvial corridors. The study also highlights the challenges of dating recent fluvial sediments and proposes a multi-proxy dating methodology using POPs contamination trends.

Mots clés: Age-depth model; depositional environment; natural archive; polybrominated diphenyl ethers; polychlorinated biphenyls; sediment core

Domaines: Milieux et Changements globaux; Environnement et Société

Sophia Vauclin, Brice Mourier, André-Marie Dendievel, Nicolas Noclin, Hervé Piégay, et al.. Depositional environments and historical contamination as a framework to reconstruct fluvial sedimentary evolution. Science of the Total Environment, 2021, pp.142900. ⟨10.1016/j.scitotenv.2020.142900⟩. ⟨hal-03070723⟩