Kasumigaura Environmental Science Center, 1854 Okijyuku, Tsuchiura, Ibaraki 3000023, Japan; Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 3058572, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 3058572, Japan; Laboratory for Ecological Reconstruction Science Co. Ltd., 5-80 Aioicho, Naka-ku, Yokohama, Kanagawa 2310012, Japan.
Sci Total Environ. 2018 Feb 15;615:741-750. doi: 10.1016/j.scitotenv.2017.09.286. Epub 2017 Oct 17.
Vertical profiles of radiocesium concentrations were measured in sediment cores collected at various times after the 2011 Fukushima nuclear accident in five Japanese lakes (Hinuma, Kasumigaura, Kitaura, Onogawa and Sohara) with different morphological and trophic characteristics in order to investigate the sedimentation-diffusion processes. In lakes where sediments had high porosities and experienced considerable wave action due to shallowness, we observed rapid penetration of radiocesium to a certain depth just after the accident, followed by downward movement of the peak depths. In contrast, gradual downward transfers of distinct peaks were found in other types of lakes. A one-dimensional differential sediment model with water-sediments interaction processes was constructed to describe the vertical shift of radiocesium profiles. Our proposed submodels relating to the length scales of the mixing using wind-induced stress and porosity of sediments were constructed based on one measurement of the vertical distribution of radiocesium in three lakes (Hinuma, Kasumigaura and Sohara). This model was then validated using samples from those lakes in different years, as well as from two other lakes. Good agreement was obtained. We discuss our findings, the limits of model application, and future research targets.
对 2011 年福岛核事故后不同形态和营养特征的五个日本湖泊（琵琶湖、霞浦、北浦、小野川和相原）采集的沉积物芯进行了放射性铯浓度的垂直分布测量，以研究沉积-扩散过程。在那些由于水深较浅而具有高孔隙度和经历大量波浪作用的湖泊中，我们观察到放射性铯在事故发生后不久就迅速穿透到一定深度，然后峰值深度向下移动。相比之下，在其他类型的湖泊中则发现了放射性铯的明显峰值逐渐向下转移。建立了一个具有水-沉积物相互作用过程的一维差分沉积模型来描述放射性铯剖面的垂直迁移。我们基于三个湖泊（琵琶湖、霞浦和相原）的一个放射性铯垂直分布测量结果，构建了与风引起的应力和沉积物孔隙度相关的混合长度尺度有关的亚模型。然后使用不同年份以及另外两个湖泊的这些湖泊的样本对该模型进行了验证。得到了很好的一致性。我们讨论了我们的发现、模型应用的局限性和未来的研究目标。
