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 ¹³⁷Cs 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 ¹³⁷Cs at 120 h ranged from 0.3% to 3.3%, suggesting that most of the ¹³⁷Cs in the litter was hardly leachable in water. The leachable fraction of ¹³⁷Cs generally decreased with the decomposition level of the litter, implying that the easily leachable ¹³⁷Cs 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 ¹³⁷Cs and ranged from 22.7% to 54.8%. The leaching speeds of ¹³⁷Cs 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 ¹³⁷Cs cycle in forest ecosystems.