Abstract
Radioactive cesium in environment is derived from atmospheric deposition which is originated from weapon testing (1945~1960s) and Chernobyl accident(1986) fallouts. It is possible to estimate 137Cs transportation, concentration and circulation in forest ecosystem as an atmospheric deposition indicator, because 137Cs has long half-life period, 30 years, and is left for a long term in environment. It have been well known that 137Cs is kept being accumulated in surface soil, even though it passed more than 20 years from Chernobyl accident.
The soil samples were collected at 4 sites at the southwest foot of Mt. Iwaki, Aomori, Japan, and analyzed for 137Cs by gamma-ray multi-channel analyzer with a Ge-Li detector, 20 elements by X-ray fluorescence spectrometry, C and N contents by pyrolysis-gas chromatographic Analysis and loss on ignition of the soil samples. The maximum 137Cs concentration in soils was 487Bq/kg. Soil 137Cs was detected mostly within surface 10cm layer at most sites. Vertical soil 137Cs profile indicates the logarithmic decrease with increase in depth, and is similar to that of loss on ignition and Pb content. No apparent peaks corresponding to both the testing and accident fallouts were found in 137Cs soil profile in a beech forest of Mt. Iwaki, such as ones in swamp (Audry et al.,2004). Appling soil mixing model with a self-consistent least-squares method, it is suggested that most chemical concentrations of elements are explained by mixtures of four kinds of soil constituents with individual different chemical compositions. Thus, findings indicate that soil 137Cs is contained in organic matter, 25%, and clay, 75%, respectively, and most of 137Cs in surface soil is inorganically bounded to clay.
