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

[摘要] At stations on the Natsui River and the Same River in Fukushima Prefecture,Japan, effects of a heavy rain event on radiocesium export were studiedafter Typhoon Roke during 21–22 September 2011, six months after theFukushima Dai-ichi Nuclear Power Plant accident. Radioactivity of ¹³⁴Csand ¹³⁷Cs in river waters was 0.009–0.098 Bq L⁻¹ in normal flowconditions during July–September 2011, but it increased to 0.85 Bq L⁻¹ inhigh flow conditions because of heavy rains occurring with the typhoon. Theparticulate fractions of ¹³⁴Cs and ¹³⁷Cs were 21–56% of totalradiocesium in the normal flow condition, but were close to 100% afterthe typhoon. These results indicate that the pulse input of radiocesiumassociated with suspended particles from land to coastal ocean occurredbecause of the heavy rain event. Export flux of ¹³⁴Cs and ¹³⁷Csattributable to the heavy rain accounts for 30–50% of the annualradiocesium flux from inland to coastal ocean region in 2011. Results showthat rain events are one factor contributing to the transport and dispersionof radiocesium in river watersheds and coastal marine environments.

[学科分类] 地球化学与岩石