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

Abstract

A sediment core collected from the Sun Moon Lake in middle Taiwan was investigated for ²¹⁰Pb and ^239,240Pu. Based on the decrease of excess ²¹⁰Pb 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 ¹⁴C-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 ²¹⁰Pb and ^239,240Pu are 54.5 dpm cm⁻² and 0.21 dpm cm⁻², respectively. This ²¹⁰Pb inventory requires a flux of 1.7 dpm cm⁻² yr⁻¹ at steady state, which is similar to ²¹⁰Pb fluxes observed at other sites in the western Pacific rim. The inventory of ^239,240Pu is in excellent agreement with documented cumulative ^239,240Pu from global fallout (0.96 ± 0.07 mCi km⁻²) at the 20–30°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.