Transfer of137Cs from soil to plants in a wet montane forest in subtropical Taiwan

Abstract

The distribution of137Cs in an undisturbed, multistoried, subtropical wet montane forest ecosystem surrounding Yuanyang Lake (lake surface level ca. 1670m, in northeastern Taiwan), was investigated. The mossy forest here represents a currently-rare perhumid temperate environment in subtropical region. The radioactivity concentration of137Cs was determined by γ-spectroscopy with a Ge(Li) detector. Although the soil is extremely acidic (pH 3.3 to 3.6) and the rainfall is high,137Cs is evidently retained in the organic layer. The radioactivity concentration of137Cs in surface soil ranges from 28 to 71 Bq·kg−1. The concentrations of137Cs in the ground moss layer and litter were much lower than that in the soil organic layer, this suggests that137Cs detected is not from the newly deposited radioactive fallout. The radioactivity concentration and transfer factor (TF) of137Cs varied with plant species. Shrubs and ferns have higher values than a coniferous tree (Taiwan cedar). The TF in this ecosystem is as high as 0.21 to 1.88. The high values of TF is attributed to the abundance of the organic matter in the forest soils. The rapid recycling of137Cs through the soil-plant system of this undisturbed multistoried ecosystem suggests the existence of an internal cycling that help the accumulation of137Cs in this ecosystem.