Export of <sup>134</sup>Cs and <sup>137</sup>Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011

Abstract

Effects of a heavy rain event on radiocesium export were studied at stations on the Natsui River and the Same River in Fukushima Prefecture, Japan after Typhoon Roke during 21–22 September 2011, six months after the Fukushima Daiichi Nuclear Power Plant accident. Radioactivity of ¹³⁴Cs and ¹³⁷Cs in river waters was 0.011–0.098 Bq L⁻¹ at normal flow conditions during July–September in 2011, but it increased to 0.85 Bq L⁻¹ in high flow conditions by heavy rains occurring with the typhoon. The particulate fractions of ¹³⁴Cs and ¹³⁷Cs were 21–56% in the normal flow condition, but were close to 100% after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred by the heavy rain event. Export flux of ¹³⁴Cs and ¹³⁷Cs by the heavy rain accounts for 30–50% of annual radiocesium flux in 2011. Results show that rain events are one factor controlling the transport and dispersion of radiocesium in river watersheds and coastal marine environments

Fukushima Daiichi–Derived Radionuclides in the Ocean: Transport, Fate, and Impacts

“…Radiocesium inputs to Japanese coastal waters also occur via riverine sources and surface water runoff (Chartin et al 2013, Nagao et al 2013, Evrard et al 2015. Cs has a high affinity for particles in freshwater, and thus its transport and delivery via rivers are associated largely with high sediment loads that occur during heavy rains and flood events.…”

134Cs and 137Cs in the Seawater Around Japan and in the North Pacific

“…2.12 ), possibly caused by the fl uvial input of terrestrial FNPP-derived radioactive Cs. Nagao et al ( 2013 ) reported the transport of FNPP-derived radioactive Cs from a contaminated watershed in Fukushima Prefecture to the coastal ocean area during July and December 2011; they estimated the export fl ux of 134 Cs and 137 Cs after the heavy rain event (Typhoon Roke in September 2011) as roughly 0.74-2.6 × 10 10 Bq day −1 for the rivers of Fukushima Prefecture. These values account for 30-50 % of the export of radioactive Cs for the 10 months of March 11-December 31, 2011 in these rivers (Nagao et al 2013 ).…”

“…Nagao et al ( 2013 ) reported the transport of FNPP-derived radioactive Cs from a contaminated watershed in Fukushima Prefecture to the coastal ocean area during July and December 2011; they estimated the export fl ux of 134 Cs and 137 Cs after the heavy rain event (Typhoon Roke in September 2011) as roughly 0.74-2.6 × 10 10 Bq day −1 for the rivers of Fukushima Prefecture. These values account for 30-50 % of the export of radioactive Cs for the 10 months of March 11-December 31, 2011 in these rivers (Nagao et al 2013 ). In the future, secondary dispersion of FNPP-derived radioactive Cs through rivers, as considered in Nagao et al ( 2013 ), and through groundwater should be studied to understand the long-term effects of the FNPP accident in the coastal area of East Japan.…”

“…These values account for 30-50 % of the export of radioactive Cs for the 10 months of March 11-December 31, 2011 in these rivers (Nagao et al 2013 ). In the future, secondary dispersion of FNPP-derived radioactive Cs through rivers, as considered in Nagao et al ( 2013 ), and through groundwater should be studied to understand the long-term effects of the FNPP accident in the coastal area of East Japan. …”

Horizontal and vertical distributions of 137Cs in seabed sediments around the river mouth near Fukushima Daiichi Nuclear Power Plant

“…It is likely that these rapid changes and multiple peaks are related to the release of 137 Cs from the Ukedo River. Several heavy-rain events, which were considered to be a cause of significant export flux of 137 Cs from inland to the coastal region (Nagao et al 2013), were observed in the Ukedo River Basin from September 2011 to October 2013 (e.g., Typhoon Roke, September 2011; Typhoon Man-yi, September 2013). Rapid changes and multiple peaks of the 137 Cs distribution obtained in this study were inferred to be related to pulse-input by the heavyrain events.…”