Erosion in Mediterranean mountain landscapes during the last millennium: a quantitative approach based on lake sediment sequences (Iberian Range, Spain)

Abstract

Land degradation and soil erosion are key environmental problems in Mediterranean mountains characterized by both a long history of human occupation, and strong seasonality of hydrological regimes. Experimental monitored catchments have identified main controlling factors on erosion dynamics, but because of the short time span of the instrumental measurements they do not integrate the complete temporal and spatial variability of these environments. To obtain some long-term series of Mediterranean landscape evolution we propose a novel strategy based on multi-proxy analyses of lake sediments aimed to quantify sediment delivery and erosion dynamics. Karstic lakes in the Iberian Range (Central Spain) provide an opportunity to reconstruct the depositional evolution of the watersheds and to evaluate the response to both, the variable anthropogenic impacts and climate forcings during the last 1000years.The most significant periods of increased sediment delivery (26–483Tkm yr−1) in the Iberian Range sites took place during the 15th–16th and 18th–19th centuries as a result of large land use changes and land clearing. Positive synergies between increasing human population and more humid periods led to peaks in sediment deliver during some phases of the Little Ice Age. Recent changes associated with the rural exodus and land abandonment during mid-20th century are more clearly shown in larger watersheds by decreased sediment delivery to the lakes due to the re-vegetation of the landscape (6–200Tkm yr−1).This new integrated approach based on long-term lake sequences provides a longer perspective of erosion processes in Mediterranean watersheds and validates the main factors identified in monitoring surveys (land cover and surface formations erodibility). In both settings, lakes and experimental catchments, most sediment delivery occurs during flooding events. Measured and reconstructed values show comparable large ranges, underlying the punctuated nature of sediment dynamics in Mediterranean landscapes at decadal and centennial scales.