Effect of the Fukushima Daiichi nuclear power plant accident on radiocesium distribution in tea fields in Saitama Prefecture: Intercultivar differences

We investigated radiocesium distribution in tea plants (Camellia sinensis L. var. sinensis) of Saitama Prefecture, located approximately 200–250 km away from Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant. In 2012, more than 2500 samples of tea plants were analyzed. We found differences in radiocesium concentration among tea plant cultivars, which appeared to be attributable mainly to the leaf morphology and depth of the leaf layer in tea plants. Furthermore, the radiocesium concentration in the first tea crop showed a strong correlation with that in spring skiffing.     

Siltation and radiocesium pollution of small lakes in different catchment types far from the Fukushima Daiichi nuclear power plant accident site

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL⁻¹ and was below the Japanese standard (10 BqˑL⁻¹). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL⁻¹) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL⁻¹) and forest (0.7–5.2 BqˑL⁻¹) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha⁻¹ yr⁻¹ following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr⁻¹ for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha⁻¹) contents.