Variation of radiocesium concentration at winter thermal stratification in Lake Akagi Onuma

Abstract

Due to the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant on March 11, 2011, a large amount of radiocesium was released into the atmosphere and the ocean. It has been reported that the concentration of total radiocesium in the lake water of Lake Akagi in Gunma Prefecture is decreasing more slowly compared to other lake and pond water systems. The cause of this is considered to be the low water exchange ability due to the closed nature of the lake and the elution of radiocesium from the bottom sediments during the summer. Previous studies have suggested the increase in radiocesium concentration in the bottom water during the summer is caused by elution of radiocesium from the sediments. In this study, we investigated the concentration of radiocesium in the bottom water of Lake Akagi during the winter season of 2022 to 2024, when stratification progresses similarly to the summer.