Search

Artificial radionuclides including radiocesium (134 Cs and 137 Cs) 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 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. [ABSTRACT FROM AUTHOR]

Purpose: Spectrocolourimetric measurements provide a relatively inexpensive, quick and non-destructive alternative to the analysis of geochemical and organic matter properties. When used in the analysis of sediments and their potential sources, these colour parameters may provide important information on the dominant processes (i.e. erosion) occurring in the Critical Zone. Here, they are used to investigate whether eroded sediment is derived from forest (i.e. natural), cultivated (i.e. anthropogenic) or subsoil sources in order to assess their potential to monitor the effect of decontamination in regions impacted by fallout from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Materials and methods: Fifteen spectrocolourimetric properties (L*, a*, b*, C*, h, x, y, z, L, a, b, u*, v*, u', v') were measured in potential source (n = 37) and sediment (n = 400) samples collected during 13 campaigns from 2011 to 2017 after major flood events in two catchments (total surface area of 450 km2) draining the main FDNPP radioactive pollution plume. Potential sources included topsoil from forest and cultivated sources along with subsoil material originating from landslides, channel banks and the decontamination of cultivated areas. The optimum set of parameters used in the mixed linear model to calculate the sediment source contributions was obtained through the use of a range test, the Kruskal–Wallis H test and a linear discriminant analysis. Results and discussion: Nine selected colour parameters correctly classified 100% of the source samples (i.e. forest, subsoil and cultivated sources). The results illustrate that cultivated landscapes were the main source of sediment to these river systems (mean 56%, SD 34%) followed by subsoil (mean 26%, SD 16%) and forest sources (mean 21%, SD 24%). However, these contributions varied strongly over time, with a peak of subsoil contributions (mean 57%, SD 17%) in Fall 2015, coinciding with the occurrence of a typhoon after the remediation works. These results were consistent with monitoring studies conducted in the same area that showed the major impact of typhoon Etau in September 2015 on sediment and radiocaesium fluxes. Conclusions: These original results demonstrate that spectrocolourimetric measurements may contribute to the routine monitoring of the effectiveness of remediation works in this post-accidental context. Owing to the inexpensive, rapid and non-destructive analyses, spectrocolourimetric-based tracing methods have significant potential to provide information on the dominant erosion processes occurring in the Critical Zone. [ABSTRACT FROM AUTHOR]

Summer typhoons and spring snowmelt led to the riverine spread of continental Fukushima fallout to the coastal plains of Northeastern Japan and the Pacific Ocean. Four fieldwork campaigns based on measurement of radioactive dose rates in fine riverine sediment that has recently deposited on channel bed-sand were conducted between November 2011 and May 2013 to document the spread of fallout by rivers. After a progressive decrease in the fresh riverine sediment doses rates between 2011 and early spring in 2013, a fifth campaign conducted in November 2013 showed that they started to increase again after the occurrence of violent typhoons. We show that this increase in dose rates was mostly due to remobilization of contaminated material that was temporarily stored in river channels or, more importantly, in dam reservoirs of the region during the typhoons. In addition, supply of particles from freshly eroded soils in autumn 2013 was the most important in areas where decontamination works are under progress. Our results underline the need to monitor the impact of decontamination works and dam releases in the region, as they may provide a continuous source of radioactive contamination to the coastal plains and the Pacific Ocean during the coming years. [ABSTRACT FROM AUTHOR]

Spectrocolorimetric properties provide a quick, low-cost and non-destructive alternative to the measurement of geochemical and organic matter parameters. Their potential to discriminate between forest, cultivated and subsoil sources was tested in soils and sediment collected in coastal catchments draining the main radioactive pollution plume of Fukushima Prefecture, Japan.Fifteen spectrocolorimetric properties were determined in potential source (n=37) and sediment (n=400) samples collected during 13 campaigns from 2011–2017 in two catchments (covering a total surface area of 450 km²) draining the main radioactive pollution plume. Potential sources included topsoil from forest and cropland sources along with subsoil material originating from landslides, channel banks and the decontamination of cultivated areas. The optimum set of parameters used in the mixed linear model to calculate the sediment source contributions was obtained through the use of a range test, the Kruskal-Wallis H-test, and a linear discriminant analysis. Nine colour parameters correctly classified 100% of the source samples (forest, subsoil and cultivated sources). The results illustrate that cultivated landscapes were the main source of sediment to these river systems (mean 56%, SD 34%) followed by subsoil (mean 26%, SD 16%) and forest sources (mean 21%, SD 24%). However, these contributions strongly varied over time, with a peak of subsoil contributions (mean 57%, SD 17%) in Fall 2015, coinciding with the occurrence of a typhoon after the remediation works. These original results demonstrate that spectrocolorimetric measurements provide a powerful tool for the monitoring of the effectiveness of remediation works in this post-accidental context. [ABSTRACT FROM AUTHOR]