Distribution of the radionuclide 137Cs in the soils of a wet mountainous forest in Taiwan

The behavior of 137Cs was studied in the Yuanyang lake ecosystem, a wet mountainous forest in subtropical Taiwan. Soils investigated are either partially podzolic soils or nearly pure peats with a high organic matter concentration in the surface layer. Concentration of 137Cs was highest in the organic surface layers, particularly in the Oe horizon or in the underlying A horizon. The downwards migration to the mineral horizons is limited, in spite of the high rainfall. Topography is a critical factor for the distribution of 137Cs. It is shown that the concentration of 137Cs is highest at the foot of the slope and lower near the summit and near the lakeshore. The variation of the concentration along the landscape has been attributed to erosion-deposition in combination with surface run-off of the undisturbed forest. The amount of 137Cs in the site studied is significantly higher than at any other place in Taiwan. The accumulation of 137Cs is attributed to the high rainfall, which brought large amounts of 137Cs with the precipitation in the early 1960s. A very remarkable feature of the ecosystem is that 137Cs is not leached to the subsoils, but is stored in the biomass. Due to permanent recycling it remains available, without being leached downward