Abstract
Abstract. Topographic effects on Cs-137 concentrations in a forested area were quantitatively examined using 58 soil core samples collected in a village in Fukushima, Japan, which was directly impacted by the radioactive plume emitted during the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. In this study, five topographic parameters and two soil properties were evaluated as controls on the soil Cs-137 concentration using generalized additive models (GAMs), a flexible statistical method for evaluating the functional dependencies of multiple parameters. GAMs employing soil dry bulk density, mass water content, and elevation explained 54 % of the observed concentrations of Cs-137 within this landscape, whereas GAMs employing elevation, slope, and upslope distance explained 47 % of the observed concentrations, which provide strong evidence of topographic effects on Cs-137 concentrations in soils. The model fit analysis confirmed that the topographic effects are strongest when multiple topographic parameters and soil properties are included. The ability of each topographic feature to predict Cs-137 concentrations was influenced by the resolution of the digital elevation models. The movement of Cs-137 into the subsurface in this area near Fukushima was faster in comparison to regions affected by the Chernobyl Nuclear Power Plant accident. These results suggest that the effects of topographic parameters should be considered carefully in the use of anthropogenic radionuclides as environmental tracers and in the assessment of current and future environmental risks due to nuclear power plant accidents.
Highlights
On 11 March 2011, a 9.0 magnitude earthquake occurred near the northeast coast of Honshu, the largest island of Japan
When measured in kBq kg−1, the Cs-137 values clustered in six bins, and 41 % of the core samples were in the 100–300 kBq kg−1 interval (Fig. 4a: red)
While much previous research focused on documenting Cs-137 concentrations in nearby environments, there has been no systematic and quantitative study that examined the effect of topographic indices and soil properties on the concentration and distribution of Cs-137 from this accident
Summary
On 11 March 2011, a 9.0 magnitude earthquake occurred near the northeast coast of Honshu, the largest island of Japan. A subsequent power outage caused the water circulation pumps to fail. This led to overheating of the water, meltdowns, and hydrogen explosions (IAEA, 2015; Mahaffey, 2014). Cs-137 contamination data before the FDNPP accident were unavailable for the study site. The 1 m resolution DEM was provided by the Forestry and Forest Products Research Institute, Japan. Its original datum was GCS JGD 2011 (Zone 9), and the data collection year was 2012. The 10 m resolution DEM was downloaded from the Geospatial Information Authority of Japan Its file date was 1 October 2016, and the original datum was GCS JGD 2000. The coordinate projection of all GIS files, including DEMs, was set to UTM 54N (WGS 1984)
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