Leaching characteristics of 137Cs for forest floor affected by the Fukushima nuclear accident: A litterbag experiment. (February 2021)

• Record Type: Journal Article
• Authors: Sakuma, Kazuyuki; Yoshimura, Kazuya; Nakanishi, Takahiro
• Is Part Of: Chemosphere. Volume 264(2021)Part 1
• Publication Date: 2021-02
• Subjects: Radiocesium -- Forest litter -- Leaching -- Fukushima nuclear accident -- Litterbag; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2020.128480
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: In forest ecosystems, forest litter is considered an active medium for radiocesium ( 137 Cs). To understand discharge mechanisms of highly bioavailable dissolved 137 Cs from forests to river systems, we investigated the characteristics of 137 Cs leaching from forest litter as observed from litterbag experiments. Leaching experiments with conifer needle and deciduous broadleaf litters were then conducted. After soaking conifer needles and broadleaf litters for 20 min, 140 min, and 1 day, the mean values of the 137 Cs leaching ratios were 0.13–2.0% and 0.81–6.6%, respectively, indicating that 137 Cs leaching ratios are different between forest litter types. To elucidate the factors affecting 137 Cs leaching from forest litter, a multi-regression analysis of 137 Cs leaching ratios was conducted against antecedent mean precipitation and temperature before sampling the litterbag and accumulated temperature during the litterbag experiments. The 137 Cs leaching ratios showed a negative correlation to the antecedent mean precipitation for both litters and the accumulated temperature for broadleaf litters, whereas it exhibited a positive correlation with the antecedent mean temperature for both litters and the accumulated temperature for conifer needle litters. It was proposed that the fraction of 137 Cs in labile sites in forest litter increased/decreased due to litter decomposition by antecedent/accumulated temperature, and that this fraction can be washed off by the antecedent precipitation. The different effects of accumulated temperature on 137 Cs leaching from conifer needles and broadleaf litters could be due to their different decomposition rates. Our results contribute further the understanding of the mechanisms associated with dissolved 137 Cs discharge from forested catchments. Graphical abstract: Image 1 Highlights: Dissolved 137 Cs leaching from forest litters was investigated. We estimated 137 Cs leaching ratios from different types of forest litters. 137 Cs leaching ratios were different from conifer needle and broadleaf litters. Initial 137 Cs leaching rates were faster than those thereafter. 137 Cs leaching from forest litters could be rationalized by environmental factors.