Matisoff Gerald
Department of Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH, USA 44106-7216.
J Environ Radioact. 2017 Feb;167:222-234. doi: 10.1016/j.jenvrad.2016.11.015. Epub 2016 Nov 23.
In lakes with a large surface area to watershed ratio Cs 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 Cs in the historical atmospheric fallout record with Cs 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 Cs profile is not an exact replica of the fallout history. Instead, the sediment reflects post-depositional processes such as resuspension, bioturbation, partitioning of Cs between the sediment solids and the pore fluids, and molecular diffusion of Cs 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 Cs 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.
在表面积与流域面积比值较大的湖泊中，铯的输送主要是通过大气直接沉降到湖面，沉积物中的铯活度已被用于估算生物体的暴露情况和沉积物质量沉积速率。将历史大气沉降记录中的铯与沉积物岩芯中的铯活度剖面进行比较，结果表明，虽然沉降沉积最大值的总体特征可以与岩芯中的活度峰值相匹配，但铯剖面的总体形状并非沉降历史的精确复制品。相反，沉积物反映了沉积后的过程，如再悬浮、生物扰动、铯在沉积物固体和孔隙流体之间的分配，以及铯通过孔隙流体的分子扩散。本文提出了一个模型，该模型将这些过程与一个系统时间平均（STA）模型相结合，该模型考虑了铯沉降的时间历史以及颗粒在水柱或受再悬浮影响的“活跃”表层沉积物中的停留时间。通过比较这些主要过程中每个过程的系数的合理范围，并将该模型应用于从两个大型浅水湖泊——伊利湖（美国/加拿大）和温尼伯湖（加拿大）采集的岩芯，对沉积物剖面进行了研究。结果表明，包含分子扩散和沉积物再悬浮的STA模型最能描述这些大型浅水湖泊的数据。
