Activities and geochronology of 137Cs in lake sediments resulting from sediment resuspension

Publication date: Available online 23 November 2016
Source:Journal of Environmental Radioactivity
Author(s): Gerald Matisoff
In lakes with a large surface area to watershed ratio ¹³⁷Cs delivery is primarily by direct atmospheric fallout to the lake surface, where its activity in the sediments has been used to estimate the exposure to organisms and sediment mass deposition rates. Comparison of ¹³⁷Cs in the historical atmospheric fallout record with ¹³⁷Cs activity profiles in sediment cores reveals that although the general features of a maxima in the fallout deposition can be matched to activity peaks in the core, the general shape of the ¹³⁷Cs profile is not an exact replica of the fallout history. Instead, the sediment reflects post-depositional processes such as resuspension, bioturbation, partitioning of ¹³⁷Cs between the sediment solids and the pore fluids, and molecular diffusion of ¹³⁷Cs through the pore fluids. Presented here is a model that couples these processes to a system time averaging (STA) model that accounts for the time history of ¹³⁷Cs fallout and the particle residence time in the water column or in the 'active' surface sediment subject to resuspension. Sediment profiles are examined by comparing reasonable ranges of each of the coefficients of each of these major processes and by applying the model to cores collected from two large, shallow lakes, Lake Erie (USA/Canada) and Lake Winnipeg (Canada). The results indicate that the STA model with molecular diffusion and sediment resuspension best describes the data from these large, shallow lakes.

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