5:15 PM - 6:45 PM
[AHW22-P14] Amount of radiocaesium transferred in stream and river water in the towns of Namie and Futaba, Fukushima
Keywords:radiocaesium, river water, suspended sediment, dissolved ions, multi-elements, TEPCO Fukushima Dai-ichi Nuclear Power Stations
Due to the TEPCO Fukushima Daiichi Nuclear Power Stations accident, approximately 10×1015 Bq of 137Cs was released into the environment (Terada et al., 2020), of which about 30%, or about 2.7×1015 Bq, have been deposited in the terrestrial environment (Onda et al., 2020). Calculated of 137Cs accumulation in Fukushima Prefecture shows that forests and paddies field account for about 74% and 10%, respectively (Kato et al., 2019). Cs in forest soils is strongly adsorbed to clay minerals, whereas particulate matter in river water is mainly derived from forest soils. It is suggested that Cs adsorbed particulate matter in the river also continuously transported from forest to river. Therefore, it is important to obtain continuously radiocasium(134Cs, 137Cs)data in headwaters and surrounding rivers to clarify the amount of Cs transferred in the terrestrial environment.
In this study, the 134Cs and 137Cs activity concentrations and the migration of 137Cs were calculated for three forms of existence (dissolved form, suspended form and suspended sesiment) in the stream water surrounding the Juman Mountain and in the river water of the Saruta River in Namie town and the upper stream of the Maeda River in Futaba town, Fukushima Prefecture. The Saruta River and the upper stream of the Maeda River are mostly covered by forests in the basin (JAXA high-resolution land use cover map, https://www.eorc.jaxa.jp/ALOS/jp/dataset/lulc_j.htm). Another objective was to clarify the relationship between dissolved radiocasium activity concentrations and dissolved organic carbon and dissolved ions (Ca2+, NO3-, etc.). For radiocasiumactivity concentrations of suspended sediments, identify the correlation with elemental concentrations (Ca, Sr, Mo, etc.).
The estimated amount of 137Cs transferred from suspended sediments during June-August 2023 at the middle stream station of the Saruta River was 1.36×108-1.79×108 Bq/month, which is within the range of values at nine rivers in the Hamadori region of Fukushima Prefecture as of December 2020 (2.98×106-8.45×109 Bq/month, Fan et al., 2024). On the other hand, the 137Cs amounts in this study were an order of magnitude lower than the suspended 137Cs transport amounts (0.227×109-18.8×109Bq/event, Niida et al., 2022) in the Niida River, Maeda River and Takase River during the three high-flow events in September 2019 and July 2020. The transport values in this study are considered to represent value of the normal water stage, taking into account of variations in water level and river discharge.
In this study, the 134Cs and 137Cs activity concentrations and the migration of 137Cs were calculated for three forms of existence (dissolved form, suspended form and suspended sesiment) in the stream water surrounding the Juman Mountain and in the river water of the Saruta River in Namie town and the upper stream of the Maeda River in Futaba town, Fukushima Prefecture. The Saruta River and the upper stream of the Maeda River are mostly covered by forests in the basin (JAXA high-resolution land use cover map, https://www.eorc.jaxa.jp/ALOS/jp/dataset/lulc_j.htm). Another objective was to clarify the relationship between dissolved radiocasium activity concentrations and dissolved organic carbon and dissolved ions (Ca2+, NO3-, etc.). For radiocasiumactivity concentrations of suspended sediments, identify the correlation with elemental concentrations (Ca, Sr, Mo, etc.).
The estimated amount of 137Cs transferred from suspended sediments during June-August 2023 at the middle stream station of the Saruta River was 1.36×108-1.79×108 Bq/month, which is within the range of values at nine rivers in the Hamadori region of Fukushima Prefecture as of December 2020 (2.98×106-8.45×109 Bq/month, Fan et al., 2024). On the other hand, the 137Cs amounts in this study were an order of magnitude lower than the suspended 137Cs transport amounts (0.227×109-18.8×109Bq/event, Niida et al., 2022) in the Niida River, Maeda River and Takase River during the three high-flow events in September 2019 and July 2020. The transport values in this study are considered to represent value of the normal water stage, taking into account of variations in water level and river discharge.