Leaching characteristics of 137Cs for forest floor affected by the Fukushima nuclear accident: A litterbag experiment

In forest ecosystems, forest litter is considered an active medium for radiocesium (Cs-137). To understand discharge mechanisms of highly bioavailable dissolved Cs-137 from forests to river systems, we investigated the characteristics of Cs-137 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 Cs-137 leaching ratios were 0.13-2.0% and 0.81-6.6%, respectively, indicating that Cs-137 leaching ratios are different between forest litter types. To elucidate the factors affecting Cs-137 leaching from forest litter, a multi-regression analysis of Cs-137 leaching ratios was conducted against antecedent mean precipitation and temperature before sampling the litterbag and accumulated temperature during the litterbag experiments. The Cs-137 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 Cs-137 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 Cs-137 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 Cs-137 discharge from forested catchments. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study found that Cs-137 leaching ratios differ between different types of forest litter, with varying effects of precipitation and temperature changes. The impact of temperature on Cs-137 leaching may be related to the decomposition rates of litter.