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Topographic heterogeneity effect on the accumulation of Fukushima-derived radiocesium on forest floor driven by biologically mediated processes

Koarashi, Jun  ; Atarashi-Andoh, Mariko ; Takeuchi, Erina; Nishimura, Shusaku

The accident at the Fukushima Daiichi Nuclear Power Plant caused serious radiocesium ($$^{137}$$Cs) contamination of forest ecosystems located in mountainous and hilly regions with steep terrain. To understand topographic effects on the redistribution and accumulation of $$^{137}$$Cs on forest floor, we investigated the distribution of Fukushima-derived $$^{137}$$Cs in forest-floor litter layers on a steep hillslope in a Japanese deciduous forest in August 2013. Both leaf-litter materials and litter-associated $$^{137}$$Cs were accumulated in large amounts at the bottom of the hillslope. At the bottom, a significant fraction (65%) of the $$^{137}$$Cs inventory was observed to be associated with newly shed and less degraded leaf-litter materials, with estimated mean ages of 0.5-1.5 years, added via litterfall after the accident. Newly emerged leaves at the site were contaminated with Fukushima-derived $$^{137}$$Cs in May 2011 (two months after the accident) and $$^{137}$$Cs concentration in them decreased with time. However, the concentrations were still two orders of magnitude higher than the pre-accident level in 2013 and 2014. These observations are the first to show that $$^{137}$$Cs redistribution on a forested hillslope is strongly controlled by biologically mediated processes and continues to supply $$^{137}$$Cs to the bottom via litterfall at a reduced rate.

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Category:Multidisciplinary Sciences

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