The horizontal distribution of soil 137Cs concentrations observed in an upland field located in the Abukuma mid-mountainous area

Abstract

Since the 2011 Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the horizontal distribution of soil radioactive Cs (rCs) concentrations within the same farmland has rarely been reported. We cultivated soybean (Glycine max) and azuki bean (Vigna angularis) in a farmers' field located in the Abukuma mid- mountainous area in Fukushima Prefecture, in 2012. Twenty-seven plots (each 2.5×3 m) were established and the respective soil 137Cs concentrations were measured at different depths. This report mainly focuses on the variabilities. First, slight differences in soil physicochemical properties were observed along the elevation. Soil 137Cs concentrations in the 0-10 cm layer averaged 0.97 kBq kg-1 -dry soil (a coefficient of variation [CV] = 17.5%). In the 10-20 cm layer, the mean value was 0.38 kBq kg-1 -dry soil, which was significantly smaller than that of the upper layer, but the CV was 51.7%, meaning higher variability than that of the upper layer. There was no correlation between soil 137Cs concentration and soil pH (H2O), cation exchange capacity, or exchangeable potassium content (Ex-K). These results suggest that two rotary tills that may been carried out by the spring of 2012 were still insufficient for uniform horizontal and depth redistribution of rCs deposited onto the soil surface layer after the FDNPP accident.