Spatial variability of the vertical migration of fallout 137 Cs in the soil of a pasture, and consequences for long-term predictions

Abstract

Various transport models are presently used to predict the long-term migration behaviour of fallout radiocesium on the soil. To examine to what extent the uncertainty of these predictions is influenced by the spatial variability of the migration rates, we determined the depth profiles of Chernobyl-derived 137Cs at 100 plots in a 100 m x 100 m pasture. These data were used to obtain the frequency distributions of the characteristic transport parameters of three widely used transport models (e.g. dispersion-convection model, residence time model, and back-flow model). The results show that these transport parameters are generally log-normally distributed with a coefficient of variation of about 80%. Finally, each transport model was employed to predict the resulting frequency distribution of the 137Cs inventory in the main root layer (0-7 cm) of the pasture, 20, 50, and 100 years after the deposition. If only the spatial variability of the transport parameters is taken into account, this analysis revealed that the dispersion-convection model and the back-flow model always predicted rather similar, but significantly higher median inventories than those obtained with the residence time model. If, in addition, the spatial variability of the amount of 137Cs deposited is also taken into account, the frequency distributions of the 137Cs inventories in the root layer become so wide that differences in the median inventories predicted by the three models become statistically significant only after 100 years. Several statistically significant correlations between the transport parameters of the three models were also detected.

Vertical migration of 60Co, 137Cs and 226Ra in agricultural soils as observed in lysimeters under crop rotation

“…Bossew and Strebl (2001), Schuller et al (1997) and Szerbin et al (1999), representing such different ecosystems like tropical rainforest, permanent pastures in Chile and Hungarian grassland soils. At an alpine pasture, Bunzl et al (2000) found also very small migration rates of 137 Cs. Evaluating more than 500 vertical distributions of radionuclides (not only radiocesium) in Austria, Bossew and Kirchner (2004) state that typical orders of magnitude of the velocities and the diffusion constants of Chernobyl-134 Cs are 0.3 cm a ÿ1 and 0.3 cm 2 a ÿ1 , respectively.…”

Site Selection and Sampling Design

“…Sutherland (1996) summarized the most complete literature review on reference sites. Bunzl et al (1997Bunzl et al ( , 2000, Schuller et al (1997), Lettner et al (2000), and Golosov et al (1999) provide more-recent information on selection of and variability within reference sites, while Pennock (2000) placed variability in reference sites in the context of variability in other soil properties.…”

New developments to support decision-making in contaminated inhabited areas following incidents involving a release of radioactivity to the environment

“…This would make long-term dose estimates for other radionuclides somewhat conservative, if based on the same migration data. The vertical migration of contaminants in soil is described in ERMIN by a one-dimensional, convectiveedispersive, local equilibrium, mass transport model, as suggested by Bunzl et al (2000). This gives the contaminant concentration as a function of depth and time, thus facilitating multiplication at different times of contamination level values at different depths by appropriate dose rate conversion factors.…”