Because of their large mobility and high bioavailability, it is necessary to elucidate the origins and dynamics of dissolved radionuclides in river and reservoir systems to assess the transfer of those radionuclides from water to crops and aquatic organisms. Elution from contaminated reservoir sediments, a potential source of dissolved radionuclides, presents a long-term concern, particularly for long-lived radionuclides. In this study, we systematically investigated caesium-137 (¹³⁷Cs) concentrations using a time-series suite of input and output water samples collected from 2014 to 2019 from the Ogaki Dam Reservoir, which has a catchment with a high ¹³⁷Cs inventory due to the Fukushima Dai-ichi Nuclear Power Plant accident. The results of our study showed that dissolved ¹³⁷Cs concentration was significantly higher in the output water than that in the main input water, and that the effective ecological half-life of dissolved ¹³⁷Cs in the output water was longer than in the main input water. We quantitatively evaluated the mass balance of dissolved ¹³⁷Cs in the reservoir to elucidate how much dissolved ¹³⁷Cs from the rivers and production from reservoir sediments contribute to ¹³⁷Cs in the reservoir output. The annual output of dissolved ¹³⁷Cs was significantly higher than the total input of dissolved ¹³⁷Cs, with approximately 32%–40% of the dissolved ¹³⁷Cs in the output water presumably being produced from reservoir sediments. Consequently, the estimated dissolved ¹³⁷Cs fluxes from reservoir sediments to overlying water were 0.57–1.3 × 10⁴ Bq m⁻² y⁻¹. This implies that approximately 0.04%–0.09% of ¹³⁷Cs accumulated in the sediments was released through elution to the overlying water each year. Reservoir sediments containing high ¹³⁷Cs levels may thus become even more important as sources of bioavailable dissolved ¹³⁷Cs in the future.

由于它们的大迁移率和高生物利用度，有必要阐明河流和水库系统中溶解的放射性核素的起源和动态，以评估这些放射性核素从水到作物和水生生物的转移。从受污染的水库沉积物（一种潜在的溶解的放射性核素）中洗脱出来是一个长期的问题，特别是对于长寿命的放射性核素。在这项研究中，我们使用了2014年至2019年从大垣水库蓄水的^137个Cs存量高的流域，使用2014年至2019年收集的输入和输出水样的时间序列套件，系统地研究了¹³⁷ Cs的浓度。福岛第一核电站事故。我们的研究结果表明，溶解输出水中的¹³⁷ Cs浓度显着高于主输入水中的¹³⁷ Cs浓度，并且输出水中溶解的¹³⁷ Cs的有效生态半衰期比主输入水中的更长。我们定量评估了水库中溶解的¹³⁷ Cs的质量平衡，以阐明河流中溶解的¹³⁷ Cs和水库沉积物的产量对水库产出中¹³⁷ Cs的贡献。溶解的年产量^137个Cs的比溶解的总输入显著更高^137个CS，与约32％-40溶解的％¹³⁷产出水中的Cs大概是由储层沉积物产生的。因此，估计从储层沉积物到上覆水的溶解¹³⁷ Cs通量为0.57–1.3×10 ⁴  Bq m ^-2 y ^-1。这意味着每年沉积物中沉积的¹³⁷ Cs中约有0.04％–0.09％是通过淋洗释放到上覆水中的。因此，作为未来生物可利用的¹³⁷ Cs的来源，含¹³⁷ Cs高的储层沉积物可能变得更加重要。