Differences in leaching characteristics of dissolved radiocaesium and potassium from the litter layer of Japanese cedar and broadleaf forests in Fukushima, Japan

Cesium is an element that belongs to the same group as K, and is known to show similar behaviour to that of K in plants. In this study, we conducted a serial leaching test for 120 h to compare the leaching characteristics of dissolved Cs-137 and K in forest litter, obtained from Japanese cedar and deciduous broadleaf forests located 40 km from the site of the 2011 Fukushima Dai-ichi nuclear power plant accident. The litter was collected in 2018 and was divided into three groups according to the decomposition level. The cumulative leachable fraction of Cs-137 at 120 h ranged from 0.3% to 3.3%, suggesting that most of the Cs-137 in the litter was hardly leachable in water. The leachable fraction of Cs-137 generally decreased with the decomposition level of the litter, implying that the easily leachable Cs-137 eluted into the water during the first stage of decomposition. Meanwhile, the cumulative leachable fraction of K at 120 h was approximately 10 times greater than that of Cs-137 and ranged from 22.7% to 54.8%. The leaching speeds of Cs-137 and K decreased suddenly with elapsed time regardless of the tree species, decomposition degree, or element. Our findings contribute to the long-term understanding of the Cs-137 cycle in forest ecosystems.