Use of Beryllium-7 to assess soil redistribution by erosion in two contrasting Mediterranean environments

In the Mediterranean region there is growing concern for the potential increase in erosion risk associated with climate change and increasing storm frequency. The central Ebro basin is the region facing the greatest problems of desertification in northern Spain and there is a need to assemble information on short-term erosion rates associated with individual storm events. The Be technique offers considerable potential to document short-term erosion rates, but to date there has been little attempt to use it in Spain. This contribution reports the results of a study aimed at using the Be technique to document short-term erosion rates associated with storm events in two study areas within the central Ebro basin and to investigate the influence of land use and slope gradient on the rates and patterns of soil redistribution. These study areas were located in the central gypsiferous plain and the mountainous area bordering the basin. In the mountain location, the Be areal activity density in the stony soils sampled along a 24% slope transect showed large variations (between 16.4 and 262.1 Bq m). Erosion dominated at most sampling points and estimated soil losses ranged between 5.5 and 40 Mg ha. On the gentler slopes of the central plain, Be inventories ranged between 20 and 170.3 Bq m and there was greater evidence of deposition as well as erosion. The highest soil redistribution rates (–42 and 33 Mg ha) were found on cultivated soils. The Be inventories suggest that soil surface characteristics, such as stone and litter cover, in addition to land use and slope gradient, may affect the pattern of soil redistribution. The two case-studies reported provide evidence of relatively high short-term erosion and soil redistribution rates associated with individual storm events and confirm the potential for using Be to assemble information on erosion and soil redistribution rates in Mediterranean environments.