[2C10-16] Fukushima 2

3:45 PM - 4:00 PM JST(6:45 AM - 7:00 AM UTC)

[2C14] Investigation on distribution of radioactive substances in Fukushima(9) Factors contributing to elevated concentrations of dissolved form Cs-137 during runoff in forest headwater catchment

*Yutaro Nagata¹, Yuichi Onda², Koichi Sakakibara³, Junko Takahashi², Tsubasa Hiramatsu³ (1. Univ. of Tsukuba, Master programme of Geosciences, 2. Univ. of Tsukuba, Center for Reaearch in Radiation, Isotopes, and Earth System Sciences, 3. Shinshu Univ. Faculty of Science)

Keywords:

Cs-137,forest headwater catchment,DOC

It has been observed that the concentration of dissolved ¹³⁷Cs increases during runoff event in forest headwater catchment affected by the Fukushima Daiichi nuclear accident. Ion exchange with K⁺ and NH₄⁺ and elution from sedimentary organic matter are thought to be the origin of dissolved ¹³⁷Cs in rivers. In this study, stream water was sampled both during normal water flow and during run-off to measure not only ¹³⁷Cs concentration but also dissolved inorganic ions and dissolved organic carbon (DOC), and to estimate the causes of the increase in the concentration of dissolved ¹³⁷Cs during run-off. The concentration of competitive ions decreased to the level of normal water 4 hours after the peak, while the concentration of DOC remained more than twice the level of normal water 12 hours after discharge. The concentrations of dissolved ¹³⁷Cs were higher than normal situations even on the day after runoff event. These results suggest that the increase in the concentrations of dissolved ¹³⁷Cs during runoff event was largely due to direct leaching from sedimentary organic matter rather than ion exchange.