The 137Cs technique applied to steep Mediterranean slopes (Part II): landscape evolution and model calibration

Abstract

Over the past years the Caesium-137 (137Cs) technique has been successfully applied in numerous environments all over the world. This technique is using the worldwide distribution of the anthropogenic 137Cs radionuclide and its redistribution associated with soil particles as an effective estimation of net soil-loss rates. In contrast to numerous studies on deep, often cultivated, clay soils with gentle to intermediate slopes, typical Mediterranean shallow stony soils on steep slopes have received less attention. In this paper, the landscape evolution over the past 37 years has been evaluated using the 137Cs technique for two lithological different areas under contrasting land use in the Álora case study area (Málaga, Spain). In soils on gneiss and serpentinite bedrock several transects have been selected on steep slopes up to 35° with mean soil depths from 37 cm for gneiss to 24 cm for serpentinite. Estimating net soil redistribution rates from radionuclide distributions depends on the calculation of the local area reference inventory and the used calibration technique. Several methods have been tested and final results were found to differ considerably. After careful parameter selection, the resulting net soil redistribution estimates for the different transects have been compared with simulations of a simple landscape evolution model, resulting in different possible scenarios of erosional response. Total net soil-loss for the study area range from 2.3±0.25 to 69.1±7.8 t ha−1 year−1 for serpentinite and gneiss slopes, respectively. Differences in total slope sediment budgets as well as differences along the transects reveal influences of landscape representation and land use. In this case the impact of soil translocation by tillage and resulting erosion rates are far more important than possible parent material induced differences. However, comparing the two sampled areas not only net rates but spatial patterns as well reveal important differences in distribution over the landscape of net erosion and net sedimentation zones.