137Cs Lake Sediment Depth Profiles and Inventories Within Four Lakes of Idaho's Sawtooth Wilderness.

Abstract

A total of 68 sediment cores from four freshwater alpine lakes in Idaho's Sawtooth Wilderness were collected during the summer of 2017. The objectives of the study were to determine depth distributions of Cs in the cores using gamma spectrometry and to estimate the sedimentation rates of the lakes from the identified geochronological peaks linked to nuclear fallout. The Cs radioactivity above reference-area values was detected in all studied lakes. The maximum Cs concentrations measured in each lake's sediment ranged from 74.0 ± 6.09 to 255 ± 7.48 Bq kg. Factors such as elevation, latitude, and pH showed no correlation to total Cs deposition. However, the data developed during this investigation suggested that characteristics such as geological location or lake flushing patterns are important factors in the total Cs deposition observed. Three of the lakes had Cs sediment depth distributions that resembled the deposition pattern of weapons testing as a function of time. Mean sedimentation rate estimates ranged from 0.08 ± 0.3 to 0.1 ± 0.05 cm y and decreased with increasing altitude.