Vertical and lateral distributions of 137Cs in cultivated and uncultivated soils on Mediterranean hillslopes

The fallout radionuclide Cs-137 has been used widely as an environmental tracer in the study of soil redistribution processes. An understanding of the relationships between Cs-137 and soil properties and physiographic factors is essential for a sound interpretation of the estimates of soil redistribution derived from Cs-137 data. The purpose of this study was to investigate the relationships of Cs-137 with main soil properties in cultivated and uncultivated soils located in the northern border of central part of the Ebro basin in order to infer the behavior of Cs-137 in representative soils of Mediterranean mountain hillslopes. The depth distribution of Cs-137 and the physicochemical properties of the soils were measured in 59 soil profiles along five soil toposequences that differed in orientation, slope gradient, land uses, soil types and lithologies, and were representative of Mediterranean mountain agroecosystems. The Cs-137 mass activities and inventories varied widely (between b.d.l. and 38 Bq kg(-1), and between 0 and 2633 Bq m(-2), respectively). The highest values were found in surface layers of uncultivated Leptosols (mean: 21.9 Bq kg(-1), 1052.0 Bq m(-2)) associated with steep slopes and high SOM content (mean: 8.3%), and the lowest values (b.d.l.) were found at deep layers of uncultivated and cultivated soils. In uncultivated soils most Cs-137 was found in the upper 12 cm with a clear exponential decay with depth. Cultivated soils had longer mixed Cs-137 profiles extending to 47 cm. Cs-137 inventories were significantly higher in uncultivated soils (mean: 1616.1 Bq m(-2)) than in cultivated soils (mean: 1174.1 Bq m(-2)). The Cs-137 contents were significantly positively correlated with SOM and stoniness, respectively, but weakly negatively correlated with clay content. Multivariate analyses were used to test the hypothesis that soil properties and physiographic factors influence the distribution of Cs-137. As much as 80% and over 60% of the variance of Cs-137 was explained by SOM contents in stepwise model and adding land use and depth intervals in GLM models evidencing the strong control of land use. The results of this study improve our understanding of the effects of soil properties and physiographic factors on the behavior of Cs-137 in the Spanish south-central Pyrenees. (C) 2013 Elsevier B.V. All rights reserved.