Vertical distributions of 137Cs in soils: a meta-analysis

International audienceThe vertical distribution of Cs-137-an artificial fallout radionuclide-is controlled by soil characteristics and processes that may differ among soil groups. The application of a single modelling approach to large number of soil profiles provides an original contribution to the literature and allows for comparison between these different soil groups. In order to quantify Cs-137 migration in soils, we compiled and modelled depth-distributed data documented in the literature published before 2013. The resulting database comprised ninety-nine Cs-137 profiles sampled in 14 soil groups of the World Reference Base (WRB) classification (FAO 1998) under different land uses or covers and collected at various geographical locations in the Northern hemisphere between 1992 and 2007. The Cs-137 profiles were classified in seven different categories according to the shape and location of radiocaesium peak. Depth of the latter ranged between 0 and 12 cm (median of 2 cm) and maximal penetration of cesium reached from 12 to 60 cm. The Cs-137 depth distributions in these soils were fitted using a diffusion-convection equation to allow comparison between different soil groups. Diffusion coefficients ranged from 0.02 to 4.44 cm(2) years(-1) in soils (median of 0.64 cm(2) year(-1)), and convection velocities varied from 0 to 0.74 cm year(-1) (median of 0.1 cm year(-1)). The model underestimated Cs-137 concentrations by a median value of 1.9 % of the total inventory in soil samples collected below a 13-cm depth. Global Cs-137 penetration velocities ranged from 0.05 to 0.76 cm year(-1) (median of 0.28 cm year(-1)) over a 25-year period. Our results showed that modelling Cs-137 depth profile with a diffusion-convection equation allowed estimating the bioturbation and clay translocation velocity in a certain number of soil groups. This quantification is crucial as these processes partially control the development of soil surface characteristics and several soil services