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Taniguchi, Keisuke*; Takeuchi, Yukio*; Fujita, Kazuki*; Dohi, Terumi; Hayashi, Seiji*; Kuramoto, Takayuki*; Nomura, Naoki*; Aono, Tatsuo*
no journal, ,
In Fukushima Prefecture, although decontamination has been completed except for difficult-to-return areas, most of the forest has not been decontaminated yet. From the forest, radiocaesium may enter rivers and affect downstream areas. A survey was conducted in three forested watersheds of the Nanokazawa, Saruta, Nuno rivers located in Fukushima Prefecture to understand the amount and characteristics of radiocaesium flowing out. In each watershed, suspended solids (SS) were collected by a suspended sand sampler, water was collected every few months, and the water level and flow rate were measured. After freeze-drying the SS sample, the concentration of suspended Cs-137 was measured by a germanium semiconductor detector. The water sample was filtered through a membrane filter with a pore size of 0.45 
m, then the dissolved Cs-137 was collected by the solid-phase extraction disk method or AMP coprecipitation method, and the dissolved Cs-137 concentration was measured by a germanium semiconductor detector. The ranges of dissolved Cs-137 concentration in FY2019 were 69-190 mBq/L in the Saruta River, 9.7-16 mBq/L in the Nanokazawa river, and ND-3.2 mBq/L in the Nuno River. In the poster, we will also present the results of SS measurements and flow observations.
Aono, Tatsuo*; Nakanishi, Takahiro
no journal, ,
In order to elucidate the distribution, behavior and runoff process of radiocaesium in stream water collected from forest catchments, the activity concentrations of dissolved and particulate radiocaesium were monitored in this area. Although there is a very strong correlation between annual mean activity concentration of dissolved Cs-137 and mean air does rate in catchment area, no features were found with activity concentrations of particulate Cs-137 and mean air does rate in the area. The river water increased due to heavy rains caused by two typhoons in October 2019, and then the topography changed drastically with the inflow of sediment. The radioactivity concentrations of dissolved Cs-137 were decreased by about 50% compared to before the heavy rain. However, the change of radioactivity concentrations of particulate Cs-137 have not been observed. It is considered that the condition of the forest basin has changed as one of reasons.