SOIL-EROSION AND REDISTRIBUTION ON CULTIVATED AND UNCULTIVATED LAND NEAR LAS-BARDENAS IN THE CENTRAL EBRO RIVER BASIN, SPAIN

The semiarid regions of Spain, including the central part of the Ebro River basin, are under threat due to desertification. Severe erosion, as a result of poor land management, has led to degradation of the soi l resource, and there is a clear need for quantitative erosion rate da ta to evaluate the problem. This study aimed to examine the potential for using caesium-137 to identify the patterns and rates of soil erosi on and redistribution within this semiarid environment. Samples for th e determination of caesium-137 were collected from uncultivated slopes and cultivated valley floor sites near the head and outlet of a small representative basin in the Las Bardenas area. The measured patterns of caesium-137 mobilization, redistribution and export provide a semiq uantitative indication of the variation in erosion within the study si te. Calibration of the caesium-137 measurements, taking account of the differing behaviour of radiocaesium on cultivated and uncultivated la nd, allows estimation of the actual rates of erosion and deposition in volved. The results show (1) the erosion rates on the cultivated land (1.6-2-5 kg m-2 yr-1) are typically more than five times those seen on the uncultivated land (0.2-0.4kg m-2 yr-1), and (2) erosion on the un cultivated land is significantly less severe at the head of the basin than at the outlet. Study of the vegetation cover suggests that lower growing shrubs and grasses may be more effective in reducing erosion i n this environment than trees.