Movements and Storages of Radiocesium in a Forest Ecosystem in Fukushima

Abstract

The disaster that occurred at the Fukushima Daiichi Nuclear Power Plant in March 2011 resulted in a massive dispersion of radioactive cesium ( 137 Cs) over vast forests and other surrounding areas. The author has conducted intensive monitoring in a water catchment area located in northern Fukushima to determine and explain how exactly 137 Cs migrates to and builds up in a forest ecosystem before being discharged from it. This monitoring revealed that the amount of 137 Cs that is discharged from the forest over the course of one year was at least two orders of magnitude less than the estimated amount of deposition immediately after the disaster. It has been suggested that the migration takes place mainly in the form of suspended solids with particulate organics serving as important carriers. The largest 137 Cs pools in the forest ecosystem proved to be the litter layer and the topsoil. The circulation of 137 Cs was also indicated within flora, including tall trees. The dispersion of 137 Cs within the biological communities of animals and other creatures was more notable in terms of migration through food webs extending from animals that feed on fallen leaves and their fragments as compared to migration through food webs extending from animals that feed on live leaves. No increase in the 137 Cs concentration was observed with the rise in the trophic level, which demonstrates that no biological accumulation took place.