Human impact on soil degradation based on 10Be cosmogenic radionuclide measurements in a semi-arid region : the Betic Sierras in southeast Spain

The European countries of the Mediterranean basin have been undergoing rapid change and development over the last thirty years. For many countries, these changes have had far reaching social and economic impacts. As a consequence, the landscape itself is undergoing rapid transformations. Large agricultural areas are being abandoned temporarily or permanently; urban growth is increasing rapidly and irrigated agriculture has been intensified. The environmental change in the Mediterranean basin has often been associated with elevated soil erosion. However, the magnitude and spatial pattern of modern erosion rates were rarely analyzed in the context of long-term changes in vegetation, climate and human occupation. The present thesis provides first quantitative data on the anthropogenic impact on erosion rates in the Betic Cordillera located in southern Spain. The long-term changes in vegetation, climate and human occupation were reconstructed at the Holocene time scale based on an extensive literature review. To assess the impact of land use changes on erosion rates quantitatively, 10Be cosmogenic nuclides-derived erosion rates were benchmarked against modern erosion rates derived from check dam infillings. Overall, modern erosion rates (87 ± 114 t km-2 yr-1; n = 37) are not significantly different from long-term erosion rates (118 ± 65 t km-2 yr-1; n = 16). The stabilization of erosion rates in non-cultivated areas in the Betic Cordillera contrasts with previous reports suggesting alarming soil loss rates for southern Spain. By contrast, mechanized agricultural areas became hot spots of human-induced erosion, with accelerated erosion rates that are 4 to 5 times the natural erosion rates.