Behavior of dissolved radiocesium in river water in a forested watershed in Fukushima Prefecture

Abstract

Dissolved radiocesium concentrations in river water in a high‐dose‐rate forest watershed in Fukushima Prefecture were investigated under base flow and storm flow conditions. Under base flow conditions, dissolved 137Cs concentrations in water (Bq/L) were relatively high in summer, and these levels were higher than particulate 137Cs concentrations (Bq/L). Under storm flow, particulate 137Cs concentration became dominant as the suspended solid concentration increased. Throughout the monitoring period, dissolved 137Cs concentrations in water (Bq/L) were higher under storm flow than base flow conditions and were positively correlated with runoff intensity. Factors influencing changes in dissolved 137Cs concentrations were investigated by measuring the 137Cs concentration of suspended solid (Bq/kg) and dissolved 137Cs of unsaturated soil water, throughfall, and rainfall, together with other main solute concentrations. The 137Cs concentration per unit weight of suspended solids in river water was not strongly correlated with runoff intensity. Additionally, dissolved 137Cs concentrations of soil water, groundwater, and rainfall were not detected, while higher dissolved 137Cs concentrations were detected in throughfall than river water. K+ concentrations were higher under storm flow than base flow, and dissolved organic carbon increased toward the peak flow rate. These findings suggested that one main factor influencing generation of dissolved 137Cs in the river water was leaching from organic material in flooded areas. However, further investigation is needed to clarify the dominant source of dissolved 137Cs in river water.

Impact of typhoons on particulate and dissolved <sup>137</sup>Cs activities in seawater off the Fukushima Prefecture: results from the SOSO 5 Rivers cruise (October 2014)

“…The discharge of 137 Cs and the ratio of discharged 137 Cs to the inventory of 137 Cs during the initial six months after the accident were estimated to be 18 TBq (3.1%) for the Abukuma River and 11 TBq (0.79%) for the 13 other rivers. These 137 Cs discharge ratios were 1-2 orders of magnitude higher than those observed after June 2011 in previous studies (Ueda et al, 2013;Tsuji et al, 2016;Iwagami et al, 2017). The impact on the ocean from the initial discharge of 137 Cs through the rivers was limited because the discharge of 29 TBq (18 TBq + 11 TBq) of 137 Cs from the Abukuma River and the 13 other rivers in the Fukushima coastal region was two orders of magnitude smaller than the direct release into the ocean of 3.5 ± 0.7 PBq from the FNPP1 (Tsumune et al, 2012) and 7.6 PBq from atmospheric deposition (Kobayashi et al, 2013).…”

Factors Controlling the Dissolved 137Cs Seasonal Fluctuations in the Abukuma River Under the Influence of the Fukushima Nuclear Power Plant Accident

“…Studies conducted after the FDNPP have shown that the upper courses of rivers, which flow through largely forested areas, organic matter plays an important role as a source of dissolved 137 Cs in river waters (Kurikami et al, 2019;Sakuma et al, 2021). It was also reported that a significant relationship existed between the temperature and the dissolved 137 Cs activity concentration (Tsuji et al, 2016), resulting in clear seasonality in the dissolved 137 Cs activity concentration, with high summer values and low winter values, while particulate 137 Cs activity concentration does not correspond closely to temperature (Nakanishi et al, 2021;. From these studies, it can be concluded that the increase in the dissolved 137 Cs activity concentration in summer is due to biological processes through which high summer temperatures accelerate the decomposition of 137 Cs-contaminated organic matter.…”

Assessing the effect of topography on Cs-137 concentrations within forested soils due to the Fukushima Daiichi Nuclear Power Plant accident, Japan

“…It is this adsorption process that makes Cs-137 an effective environmental tracer for modeling surface soil loss, reservoir sedimentation, and sediment yield (Bennett et al, 2005;Loughran et al, 1987;Lowrance et al, 1988;Mabit et al, 2007;Martz and De Jong, 1987;Pennock et al, 1995;Quine et al, 1997;Ritchie and Ritchie, 1995;Wallbrink et al, 2002;Walling et al, 2007;Xinbao et al, 1990). Water also provides an environmental pathway for Cs-137 transport; Cs-137 has a high water solubility and it can attach to sediment within surface waters (Iwagami et al, 2015;Osawa et al, 2018;Sakuma et al, 2018;Tsuji et al, 2016).…”