Natural radionuclides in the soils of a small agricultural basin in the Canadian prairies and their association with topography, soil properties and erosion

Abstract

Summary Samples taken from the A and B horizons of the soil at 160 sites in a small (178 ha) cultivated drainage basin in central Saskatchewan were analysed by gamma spectroscopy to determine the concentration of a number of natural radionuclides in the soil. The concentration of 40K, the 238U daughters 226Ra,214Pb, and 214Bi, and the 232Th daughters228Ac, 212Bi, and 208Tl was determined. A variety of soil properties and topographic variables were measured at each sampling site. Earlier studies in the basin provided net soil erosion estimates (i.e. net loss or gain) for each site. The association of isotope activities with topography, soil properties and net erosion was evaluated. Mean isotope activities for the basin were very close to mean values reported earlier for native soils in southern Saskatchewan. Differences in isotope concentrations between the A and B horizons of the soils were related to differences in the degree to which the different isotopes are taken up by plants. Isotope concentrations in the surface soil were inversely correlated with soil particle size. Variation in isotope activities within the basin appeared to be linked to soil redistribution by erosion, but in a complex manner which reflects size sorting of soil particles by erosion processes. Erosion processes seem to be at least as important as leaching processes in determining the spatial distribution of natural radionuclides in the surface soils of the study area.