Lead-210 and plutonium fallout in Taiwan as recorded at a subalpine lake

A sediment core collected from the Sun Moon Lake in middle Taiwan was investigated for Pb-210 and Pu-239,Pu-240. Based on the decrease of excess Pb-210 With depth, the mean sedimentation rate in the lake during the past half century is about 0.9 cm yr(-1), which is unequivocally supported by the appearance of the 1963 plutonium fallout maximum at 26-28 cm. The short-term sedimentation rate is one order of magnitude greater than C-14-based long-term sedimentation rates in the lake reported previously. This may be attributed to the deterioration of soil conservation associated with the construction of a dam five decades ago. Total downcore inventories of excess Pb-210 and Pu-239,Pu-240 are 54.5 dpm cm(-2) and 0.21 dpm cm(-2), respectively. This Pb-210 inventory requires a flux of 1.7 dpm cm(-2) yr(-1) at steady state, which is similar to Pb-210 fluxes observed at other sites in the western Pacific rim. The inventory of Pu-239,Pu-240 is in excellent agreement with documented cumulative Pu-239,Pu-240 from global fallout (0.96 +/- 0.07 mCi km(-2)) at the 20-30 degrees N latitudinal band. Our data suggest that the Sun Moon Lake is an ideal setting for monitoring atmospheric fallout and environmental changes in this region. (C) 1997 Elsevier Science Ltd. All rights reserved.