The total amounts of radioactively contaminated materials in forests in Fukushima, Japan

TLDR

Radioactive leakage from Fukushima Daiichi has created a heavily contaminated forested area northwest of the plant, where ongoing litter decomposition threatens further soil contamination. The study aims to quantify biomass, litter, coarse woody litter, and soil in the contaminated forest and to assess the need for prompt litter removal to prevent further soil contamination. The authors measured volumes and weights of biomass, litter, coarse woody litter, and soil within the contaminated forest. They estimated a total volume of 33 Mm³ and a dry‑matter weight of 21 Tg, indicating that litter removal is an efficient decontamination strategy.

Abstract

There has been leakage of radioactive materials from the Fukushima Daiichi Nuclear Power Plant. A heavily contaminated area (≥ ¹³⁴,¹³⁷Cs 1000 kBq m⁻²) has been identified in the area northwest of the plant. The majority of the land in the contaminated area is forest. Here we report the amounts of biomass, litter (small organic matter on the surface of the soil), coarse woody litter, and soil in the contaminated forest area. The estimated overall volume and weight were 33 Mm³ (branches, leaves, litter, and coarse woody litter are not included) and 21 Tg (dry matter), respectively. Our results suggest that removing litter is an efficient method of decontamination. However, litter is being continuously decomposed, and contaminated leaves will continue to fall on the soil surface for several years; hence, the litter should be removed promptly but continuously before more radioactive elements are transferred into the soil.