Characteristic of dissolved Cs leaching from a forest litter observed from litterbag experiment in Japanese forest affected by the Fukushima nuclear accident

Sakuma, Kazuyuki   ; Yoshimura, Kazuya  ; Nakanishi, Takahiro   

We investigated characteristic of dissolved Cs leaching from litters collected at a coniforest needle and a deciduous broadleaf forests using litterbags at upstream area of Ohta River in Fukushima. Each leaf type of litters was collected into 36 litterbags, respectively, and installed each forest floor in June and December, 2017. Triplicate samples were collected at each forest floor and readily transported to laboratory in August, December, 2017 and March, May, August, December, 2018. Samples were put in buckets and soaked in purified water. We took leaching water samples from the buckets at 20 min, 140 min, 1 day after soaking litter samples in the water. These samples were analysed about Cs activity. The main results were that the deciduous broadleaf litter showed much higher leaching ratio of dissolved Cs (0.81-7.3%, mean:3.2%) than that of the coniferous needle litter (0.15-2.1%, mean:0.80%). We analysed relationships between dissolved Cs leaching ratio from forest litter and environmental factors such as an antecedent precipitation index and an accumulated temperature by using multiple regression analysis. The prediction model can reproduce observed Cs leaching ratio within a factor of 2, and the accumulated temperature showed a positive correlation. On the other hand, the antecedent precipitation showed a negative correlation.