JpGU-AGU Joint Meeting 2020

講演情報

[E] ポスター発表

セッション記号 A (大気水圏科学) » A-HW 水文・陸水・地下水学・水環境

[A-HW33] Prediction of water and sediment dynamics from small to large scales

コンビーナ:横尾 善之(Fukushima University)、浅野 友子(東京大学)

[AHW33-P05] Factors controlling concentration of dissolved 90Sr and 137Cs in river water in the Chernobyl exclusion zone.

*松下 恒輝1五十嵐 康記2恩田 裕一1脇山 義史2Alexei Konoplev2Gennady Laptev3Sergii Obrizan4Volodymyr Demianovych4Mark Zheleznyak2 (1.筑波大学、2.福島大学 環境放射能研究所、3.ウクライナ水文気象研究所、4.チェルノブイリ エコセンター)

キーワード:チェルノブイリ流域、放射性核種の動態、ストロンチウム90とセシウム137、湿地帯、空間時間的変動

Dynamics of radionuclides, 90Sr and 137Cs, are still of great interest for mitigating radiological risks in the Chernobyl Exclusion Zone (CEZ) and its downstream area. Previous studies showed positive relationship between dissolved 90Sr concentration and water discharge and it suggest that hydrological characteristics affects the 90Sr transfer. However, in practice, the dynamics of radionuclides is closely related not only to hydrological characteristics but also to chemical characteristics and the surrounding environment. For understanding formation of solution concentration in the river water system, several studies attempted to evaluate spatial-temporal variations of factors of interest in a catchment and discussed relationship between catchment characteristics and the behavior of the factors. Such approaches can improve our understanding of radionuclides dynamics. The aim of this study is to clarify the factors controlling dynamics of radionuclides in the river water system in the CEZ and we evaluated spatial-temporal variations in dissolved 90Sr and 137Cs concentration in a small catchment. The study site was in the Sakhan catchment, locating at approximately 7 km northwest from the Chernobyl Nuclear Power Plant. Water samples were taken at main stream, tributaries and water spring points each season. The discharge rate was determined by cross-sectional survey of flow velocity and water level at the same time as water sampling. Each catchment area was made from digital elevation model (DEM) data and mean 90Sr and 137Cs inventory for each sub-catchment was determined by distribution maps of radionuclide. Moreover, the proportion of wetland in dry and wet season was calculated from satellite spectral images. In laboratory, samples were analyzed for dissolved 90Sr and 137Cs, dissolved anions and cations and Si concentration. Discharge rate at the main stream was the highest in snowmelt season and the lowest in summer. The concentration of dissolved 90Sr and 137Cs at the main stream was, as like discharge rate, high in snowmelt season and low in summer. However, the response of dissolved 90Sr concentration to discharge rate was not clear at the spring points and river water in some headwater catchments. We also found that the positive relationship between the area of wetland and dissolved 90Sr and 137Cs concentration in the snowmelt season. Previous studies have showed that “wetlands” and “high water level in the floodplain” can affect high 90Sr discharge. However, the relationship is not clear during the summer. From these results, the tight coupling between hydrological processes and the 90Sr and 137Cs concentration formation processes is suggested, and further study is necessary to elucidate the mechanisms that control the 90Sr and 137Cs concentration in the river water systems.