[A-HW20] 流域の物質輸送と栄養塩循環－人間活動および気候変動の影響－

[AHW20-P07] Dynamics of radioactive and stable cesium in a forest in Fukushima, Japan

*小林 政広¹、伊藤 優子¹、蛭田 利秀²、小川 秀樹³、橋本 正伸³、篠宮 佳樹¹、今矢 明宏⁴、大貫 靖浩⁵ (1.国立研究開発法人森林研究・整備機構　森林総合研究所、2.福島県相双農林事務所、3.福島県林業研究センター、4.国際農林水産業研究センター、5.国立研究開発法人森林研究・整備機構　森林総合研究所　東北支所)

キーワード：森林、放射性セシウム、安定セシウム

Following the Fukushima Daiichi Nuclear Power Plant accident in 2011, a large quantity of radionuclides contaminated a wide area in the Tohoku and Kanto regions of Japan. Radiocesium, which has a long half-life, was initially trapped mainly in the canopy and litter layer of forests; over time, it has gradually migrated into mineral soil. To evaluate the long-term environmental impact of radiocesium it is necessary to understand the dynamics of radiocesium in forested ecosystems. In this study, we monitored the inventory and transport of radioactive and stable cesium isotopes (Cs-137 and Cs-133) in a coniferous plantation forest in Fukushima. Cs-137 concentrations in litterfall, throughfall, litter leachate, and soil water gradually decreased throughout the monitoring period. Following infiltration, the Cs-137 concentration in soil water rapidly decreased with depth, demonstrating the strong ability of clay minerals to capture radiocesium. In contrast, the Cs-133 concentration in soil water was almost constant with depth. These findings suggest that the supply of Cs-133 from soil material due to weathering is balanced by its capture by clay minerals and leaching by flowing water.