Interception of the Fukushima reactor accident‐derived¹³⁷Cs, ¹³⁴Cs and ¹³¹I by coniferous forest canopies

TLDR

The Fukushima Daiichi nuclear power plant accident caused extensive radioactive contamination of surrounding forests. The study aimed to analyze fallout 137Cs, 134Cs, and 131I in rainwater, throughfall, and stemflow in coniferous forest plantations immediately after the accident. The authors measured these radionuclides in rainwater, throughfall, and stemflow to assess forest canopy interception. Canopy interception selectively fractionated radiocesium and 131I, leaving more than 60 % of deposited radiocesium in the canopy after five months while 131I penetrated rapidly, and radiocesium transfer to the forest floor was slower than in Chernobyl spruce forests, with half‑lives of 137Cs in cypress and cedar of 620 and 890 days, respectively.

Abstract

The Fukushima Daiichi nuclear power plant accident resulted in extensive radioactive contamination of the surrounding forests. In this study, we analyzed fallout 137 Cs, 134 Cs, and 131 I in rainwater, throughfall, and stemflow in coniferous forest plantations immediately after the accident. We show selective fractionation of the deposited radionuclides by the forest canopy and contrasting transfer of radiocesium and 131 I from the canopy to the forest floor in association with precipitation. More than 60% of the total deposited radiocesium remained in the canopy after 5 month of the initial fallout, while marked penetration of the initially deposited 131 I through the canopy was observed. The half‐lives of 137 Cs absorbed in the cypress and cedar canopies were calculated as 620 days and 890 days, respectively for the period of 0–160 days. The transfer of the deposited radiocesium from the canopy to the forest floor was slow compared with that of the spruce forest affected by fallout from the Chernobyl nuclear reactor accident.