Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8572, Japan; Institute for Environmental Informatics, IDEA Consultants, Ins., 2-2-2 Hayabuchi, Tsuzuki-ku, Yokohama, Kanagawa, 224-0025, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8572, Japan; Ibaraki Kasumigaura Environmental Science Center, 1854 Okijyuku, Tsuchiura, Ibaraki, 300-0023, Japan.
J Environ Manage. 2022 Oct 15;320:115905. doi: 10.1016/j.jenvman.2022.115905. Epub 2022 Aug 11.
Vertical radiocesium concentration profiles and inventories in sediments were measured in Lake Kasumigaura following the 2011 Fukushima Dai-ichi Nuclear Power Plant accident. Further measurements of radiocesium concentrations in suspended solids (SS) have been conducted since September 2012 in the Koise and Sakura rivers inflowing into the lake. Cesium-137 (Cs) accumulated intensively near the inflow outlets in the lake. At the lake center, the Cs inventory in sediments increased during 2011-2014; however, few changes were observed during 2014-2016. The Cs surface concentration and inventory decreased considerably in Tsuchiura-iri Bay until 3 years after the accident, indicating Cs migration. However, the rate of decrease subsequently slowed due to the Cs supply from the river. The Cs concentration in river SS declined during 2012-2015; however, it remained 1-2 orders of magnitude above its pre-accident level. The entrainment coefficient of particulate Cs in the inflows was initially higher in the Koise River but decreased exponentially more rapidly in the Koise River than in the Sakura River until 2015. Therefore, in the future, the difference in Cs concentrations will be smaller. The Cs concentration in the Koise River will continue to decrease; thus, the difference in the Cs inventory between the northern and southern parts of the lake will decrease. Total estimated amounts of Cs in the entire lake were 3.72 × 10 Bq in December 2012 and 4.18 × 10 Bq in August 2016. The accumulated amount of Cs in the entire lake based on sediment analysis was similar to the riverine input of particulate Cs based on riverine SS analysis from December 2012‒;August 2016, confirming the high trapping performance of the lake for particulate matter provided by the basin. Moreover, the amount of Cs accumulated in the lake in 2016 may have originated from comparable rates of atmospheric deposition and riverine input. These findings provide useful insights for future prediction and management of radiocesium contamination and the effects of riverine inputs in general shallow lakes.
2011 年福岛第一核电站事故发生后，对湖中的柏崎刈羽核电站放射性铯的垂直浓度剖面和沉积物储量进行了测量。自 2012 年 9 月以来，一直在流入该湖的小千川和樱川河的悬浮物（SS）中测量放射性铯的浓度。铯-137（Cs）在湖泊入流口附近大量积累。在湖中心，沉积物中的 Cs 储量在 2011-2014 年间增加；然而，在 2014-2016 年间几乎没有变化。在事故发生后的 3 年内，土浦入江湾的 Cs 表面浓度和储量显著减少，表明 Cs 发生了迁移。然而，由于河流的 Cs 供应，随后减少的速度变慢。2012-2015 年间，河流 SS 中的 Cs 浓度下降；然而，其浓度仍比事故前高出 1-2 个数量级。流入物中颗粒态 Cs 的夹带系数在小千川河最初较高，但在 2015 年之前，小千川河的指数下降速度比樱川河快得多。因此，未来两者之间的 Cs 浓度差异将更小。小千川河的 Cs 浓度将继续下降；因此，湖泊南北两部分的 Cs 储量差异将会减小。2012 年 12 月和 2016 年 8 月，整个湖泊的 Cs 总量估计分别为 3.72×10 Bq 和 4.18×10 Bq。基于 2012 年 12 月至 2016 年 8 月河流 SS 分析的河流输入，基于沉积物分析的整个湖泊中 Cs 的积累量与颗粒态 Cs 的输入量相当，证实了流域对颗粒物的高截留性能。此外，2016 年湖泊中积累的 Cs 可能源自大气沉积和河流输入的可比速率。这些发现为预测和管理放射性铯污染以及一般浅水湖泊的河流输入影响提供了有用的见解。
