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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. [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]