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Spatial and temporal variation in vertical migration of dissolved 137Cs passed through the litter layer in Fukushima forests
- Kurihara, Momo, Onda, Yuichi, Suzuki, Hiroyuki, Iwasaki, Yuichi, Yasutaka, Tetsuo
- Journal of environmental radioactivity 2018 v.192 pp. 1-9
- Cryptomeria japonica, autumn, canopy, cesium radioisotopes, forests, lysimeters, nuclear power, power plants, summer, surveys, temporal variation, winter, Japan
- We examined spatial variation in vertical ¹³⁷Cs flux from the litter layer using lysimeters combined with copper-substituted Prussian blue in two forests (deciduous broad-leaved and Japanese cedar (Cryptomeria japonica)), approximately 40 km northwest of the Fukushima Daiichi Nuclear power plant. The study ran from August 2016 to February 2017 in three periods; summer (10 Aug–4 Oct), autumn (5 Oct–30 Nov) and winter (1 Dec–27 Feb). Twenty-five and 15 lysimeters were installed in the deciduous broad-leaved and the Japanese cedar sites within 400 and 300 m² areas with 3–5 m intervals, respectively. The geometric means of the flux in the deciduous broad-leaved site were 0.51, 0.085 and 0.060 kBq/m²/month in summer, autumn and winter periods, respectively. In the Japanese cedar site, the mean fluxes were 0.45, 0.036 and 0.023 kBq/m²/month. The ratio of ¹³⁷Cs flux during the survey period to litter ¹³⁷Cs inventory was 6% and 1% on average in the deciduous broad-leaved and Japanese cedar sites, respectively. The ¹³⁷Cs flux in the summer period was much larger than those in other periods, resulting from higher precipitation in the summer. Our fine scale observation with 5 m interval showed very large spatial variation in the ¹³⁷Cs flux and the differences between maximum and minimum range from 8 to 104 times, but were mostly 20–25 times. The spatial variations in the ¹³⁷Cs flux were affected positively by those in the litter ¹³⁷Cs inventory and negatively by canopy openness.