Radiocesium mobility in different parts of the two major tree species in Fukushima

Radiocesium (Cs-137) released in the Fukushima Dai-ichi Nuclear Power Plant accident is still cycling in the forest ecosystem. We examined the mobility of Cs-137 in the external parts-leaves/needles, branches, and bark-of the two major tree species in Fukushima, Japanese cedar (Cryptomeria japonica) and konara oak (Quercus serrata). This variable mobility will likely lead to spatial heterogeneity of Cs-137 and difficulty in predicting its dynamics for decades. We conducted leaching experiments on these samples by using ultrapure water and ammonium acetate. In Japanese cedar, the Cs-137 percentage leached from current-year needles was 26-45% (ultrapure water) and 27-60% (ammonium acetate)-similar to those from old needles and branches. In konara oak, the Cs-137 percentage leached from leaves was 47-72% (ultrapure water) and 70-100% (ammonium acetate)comparable to those from current-year and old branches. Relatively poor Cs-137 mobility was observed in the outer bark of Japanese cedar and in organic layer samples from both species. Comparison of the results from corresponding parts revealed greater Cs-137 mobility in konara oak than in Japanese cedar. We suggest that more active cycling of Cs-137 occurs in konara oak.

Automated summary

Cs-137 released in the Fukushima Dai-ichi Nuclear Power Plant accident is still present in the forest ecosystem. The mobility of Cs-137 in Japanese cedar and konara oak was examined, showing differences in leaching percentages in various parts of the trees. Greater Cs-137 mobility was observed in konara oak compared to Japanese cedar. This suggests a more active cycling of Cs-137 in konara oak.