[M-AG44] 福島原発事故により放出された放射性核種の環境動態

[MAG44-03] Differences in the radiocesium deposition between evergreen coniferous and deciduous broad-leaved forests

*坂下 渉¹、三浦 覚¹、今村 直広¹、大橋 伸太¹、小松 雅史¹、篠宮 佳樹¹、荒木 眞岳¹、梶本 卓也²、小林 政広¹、齊藤 哲³、金子 真司³ (1.国立研究開発法人 森林総合研究所、2.国立研究開発法人 森林総合研究所 東北支所、3.国立研究開発法人 森林総合研究所 関西支所)

キーワード：放射性セシウム、福島第一原子力発電所事故、初期沈着、常緑針葉樹林、落葉広葉樹林

Radiocesium (¹³⁷Cs) have been released to the atmosphere by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, and the ¹³⁷Cs contaminated the forest area. In the area where dry deposition is relatively large, the canopy in coniferous forests efficiently intercept the atmospheric aerosols of dry deposition. It is reported that the total dry deposition of Chernobyl-derived ¹³⁷Cs in coniferous forests was consequently higher than that in the other land use area. In March, when the FDNPP accident occurred, there was a difference in presence or absence of needles/leaves between evergreen coniferous and deciduous broad-leaved forests. Thus, it is assumed that there was a difference in the initial dry deposition of ¹³⁷Cs between these two forests. However, the quantitative assessment for this difference have not been conducted. In this study, the total inventories of ¹³⁷Cs during 2015–2019 were investigated at both hinoki cypress forest (ECF) and the nearby deciduous broad-leaved forest (DBF) in Kawauchi Village in Fukushima Prefecture, where the dry deposition is thought to be main. Our results revealed that the median of total inventory of ¹³⁷Cs at ECF and DBF was 838 and 454 kBq/m², respectively, indicating that the total inventory at ECF was significantly larger than that at DBF. This difference of the total inventory suggests that the initial dry deposition of ¹³⁷Cs at evergreen coniferous forest was larger than that at deciduous broad-leaved forest, and this difference can be applied for the reconstruction of the past dry deposition of ¹³⁷Cs in the forest areas. Further studies about spatial distribution of these differences are expected to contribute to improving the model simulation of the past plume dynamics after the FDNPP accident.