Hugo Lepage

Suite aux séismes et au tsunami qui ont frappé les côtes japonaises le 11 mars 2011, d’importantes quantités de radionucléides ont été émises par la centrale de Fukushima Dai-Ichi. Une part non négligeable (20%) du radiocésium rejeté s’est ensuite déposée sur les sols de la Préfecture de Fukushima. Cette étude vise à développer des méthodes de traçage sédimentaire originales afin de comprendre la dispersion des particules contaminées. L’étude se concentre sur 3 bassins versants côtiers situés au nord de la centrale (bassins de la Mano – 175 km², Niida – 270 km² et Ota – 75 km²) et drainant la partie la plus contaminée du panache de pollution radioactive. Cette région connaît un climat particulièrement érosif, avec des crues printanières et le passage de typhons entre juin et octobre. Pour étudier la dispersion de la contamination radioactive initiale, des sols et des laisses de crues ont été collectés au cours de 6 campagnes de terrain (organisées tous les 6 mois entre novembre 2011 et mai 2014 après les crues printanières et les typhons estivaux). L’activité des principaux radionucléides a été mesurée par spectrométrie gamma et une sélection d’échantillons a également été analysée par activation neutronique afin de déterminer leur teneur en une vingtaine d’éléments. L’analyse de l’activité en 137Cs dans 10 carottes de sols collectées dans des rizières a confirmé la faible migration du césium en profondeur dans les sols de la région. Plus de 90 % de la contamination étaient concentrés dans les 2 cm superficiels des sols en novembre 2013. Cette contamination située à la surface du sol reste donc potentiellement mobilisable par l’érosion. Par ailleurs, la détection d’argent-110 métastable (110mAg) et le fait que ce radioisotope ait un comportement similaire à celui du césium, ont permis de l’utiliser pour tracer la dispersion de la contamination dans le bassin versant de la Niida. En effet, le rapport d’activités 110mAg/137Cs dans les sols de ce bassin est significativement différent à l’amont et à l’aval de celui-ci. L’utilisation de ce rapport et d’un modèle de mélange binaire a permis d’identifier l’occurrence de cycles d’érosion et de dispersion saisonniers de la contamination. Cependant, 110mAg ayant une demi-vie de 250 jours, il a rapidement décru et l’activité est devenue inférieure aux limites de détection à compter de mai 2013. Pour pallier sa disparition, la contribution des sols des plateaux montagneux aux sédiments transitant dans la plaine côtière a été quantifiée à partir de leur signature en 137Cs. En utilisant un modèle de mélange binaire basé sur les distributions du 137Cs à l’amont (> 20 kBq/m²) et à l’aval (< 20 kBq/m²) des bassins versants, les résultats montrent que la contribution de la zone amont diffère en fonction du bassin versant. Elle fournit une part non négligeable (≈46%) des sédiments à la rivière Niida, qui est dépourvue de barrage, à la différence de la rivière Mano (≈20 %) qui en est équipée. Ces résultats montrent donc l’impact de ce type d’ouvrage qui génère une dysconnectivité sédimentaire. Afin de préciser l’origine spatiale des sédiments contaminés transportés par ces rivières, la carte des sols des bassins versants a été utilisée. Les principaux types de sols (Andosols, Cambisols et Fluvisols) ont été caractérisés par leurs teneurs en éléments chimiques, et Sc et Yb se sont révélés être le couple d’éléments le plus discriminant. Les distributions de ces deux éléments dans les trois sources ont ensuite été utilisées dans un modèle de mélange. Les résultats montrent une contribution majoritaire (> 70 %) des Fluvisols dans les sédiments. La forte contribution de ce type de sol, que l’on trouve principalement dans les rizières, confirme donc l’érodabilité accrue de ces zones agricoles. Pour poursuivre ces travaux, l’ensemble des données acquises pourrait être utilisé pour améliorer les modèles d’érosion des sols opérant à l’échelle des bassins versants.

The Rhône River is among the main rivers of western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt yr⁻¹. Its course meets numerous dams, hydro and nuclear power plants as well as agricultural, urban and industrial areas. Moreover, with the climatic crisis we are currently facing, it is proven that the occurrence and the intensity of extreme events (floods or droughts) will increase. Therefore, it is crucial to monitor the concentrations and fluxes of suspended particulate matter (SPM) and associated contaminants to study the current trends and their evolution. In the Rhône River (from Lake Geneva to the Mediterranean Sea), a monitoring network of 15 stations (3 on the Rhône River and 12 on tributaries) has been set up in the past decade by the Rhône Sediment Observatory (OSR) to investigate the concentrations and the fluxes of SPM and associated contaminants as well as their sources. The main purpose of the OSR is to assess the long-term trend of the main contaminant concentrations and fluxes, and to understand their behavior during extreme events, such as floods or dam flushing operations. The dataset presented in this paper contains the concentrations and fluxes of SPM as well as the concentrations and fluxes of several particle-bound contaminants of concern, e.g., polychlorinated biphenyl (PCB), trace metal elements (TME) and radionuclides, the particle size distribution and the particulate organic carbon of SPM. Sediment traps or continuous flow centrifuges were used to collect sufficient amount of SPM in order to conduct the measurements, and data completion was applied to reconstruct missing values. This observatory is on-going since 2011 and the database is regularly updated. All the data are made publicly available in French and English through the BDOH OSR database at https://doi.org/10.15454/RJCQZ7 (Lepage et al., 2021).

The Rhône River is amongst the main rivers of Western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt y⁻¹. Furthermore, the course of the Rhône River meets numerous dams, hydro- and nuclear power plants, and agricultural, urban or industrial areas. Thus, suspended particulate matters (SPM) have been involved in the fate of hydrophobic contaminants such as polychlorobiphenyls (PCB), mercury (Hg) and other trace metal elements (TME), and radionuclides for decades. To investigate the concentrations and the fluxes of SPM and associated contaminants, as well as their sources, a monitoring network of 15 stations (three on the Rhône River and 12 on tributaries, from Lake Geneva to the Mediterranean Sea) has been set up in the past decade within the Rhône Sediment Observatory (OSR). A main purpose of this observatory is to assess the long term trend of the main contaminant concentrations and fluxes, and to understand their behavior during extreme events such as floods or dam flushing operations. The dataset presented in this paper contains the concentrations and fluxes of SPM as well as the concentrations and fluxes of several particle bound contaminants of concern (PCB, TME, radionuclides), the particle size distribution and the particulate organic carbon of SPM. Sediment traps or continuous flow centrifuges were used to collect sufficient amount of SPM in order to conduct the measurements. This observatory is on-going since 2011 and the database is regularly updated. All the data are made publicly available in French and English through the BDOH/OSR database at https://doi.org/10.15454/RJCQZ7 (Lepage et al., 2021).

Artificial radionuclides including radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiosilver (^110mAg) were released into the environment following the Fukushima Dai-ichi nuclear power plant accident in March 2011. These particle-bound substances deposited on soils of north-eastern Japan, located predominantly within a ∼3000 km² radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset (Evrard et al., 2021), which can be accessed at https://doi.org/10.1594/PANGAEA.928594, compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations across catchments draining ∼6450 km² during 16 fieldwork campaigns. These campaigns were conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Artificial radionuclides including radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiosilver (^110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km² radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset that can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.928594 compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Artificial radionuclides including radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiosilver (^110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km² radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset that can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.928594 compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Artificial radionuclides including radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiosilver (^110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km² radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset that can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.928594 compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Artificial radionuclides including radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiosilver (^110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km² radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset that can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.928594 compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.