Transect survey of radiocesium in soils and plants of two alpine pastures

Abstract

The spatial distribution of fallout 137Cs and natural 40K in soils and vegetation of alpine pastures growing on dystric cambisols was studied along two transects of approximately 100 m in length following the slopes from top to bottom. Ten years after the Chernobyl accident, the 137Cs-activity is still concentrated in the upper 5 cm of these soils — in most cases in the uppermost two centimeters. The variability of the radiocesium concentration in the soil along the transects is high (coefficient of variance CV=92%), whereas 40K is more homogenously distributed (CV=18%). The 137Cs concentration in the soil is not significantly related to the distance downslope indicating the absence of long-range erosion processes. The variability of the distribution of 137Cs in plants is also large (CV=91%). No significant correlation between 137Cs and 40K in vegetation was found. The resulting aggregated transfer-factors (Tag) are approximately one order of magnitude lower than reported for semi-natural environments in other upland areas in Europe. A significant relationship of the altitude with the radiocesium concentration in plants or the resulting Tag can be explained by the occurence of different plant communities along the transect. The significant positive correlation of the radiocesium content in plants with the organic matter content in soils, or with the potential activity of microorganisms indicate the importance of biological parameters for the in situ availability of radionuclides.