Using 210Pbex measurements to quantify soil redistribution along two complex toposequences in Mediterranean agroecosystems, northern Spain

Information on soil redistribution rates associated with the intricate patterns of Mediterranean agroecosystems is a key requirement for assessing both soil degradation, and off-site sediment problems that can affect downstream water bodies. Excess lead-210 (210Pbex) measurements provide a very effective means of documenting spatial patterns of rates of soil redistribution in different landscapes, but to date the approach has not been widely used in mountain Mediterranean landscapes. This research aims to use 210Pbex measurements to estimate soil redistribution rates on slopes uncultivated and under cultivation, within two complex toposequences located in the vicinity of Estaña Lake, characterized by an intricate mosaic of land use, steep slopes and anthropogenic modification (e.g. terraces and tracks), which are typical of these agroecosystems in northeastern Spain. A perceptual model is developed to account for the soil redistribution dynamics along both toposequences. This provides a simple and novel methodology adapted to Mediterranean agroecosystems, which besides using information on soil redistribution rates provided by 210Pbex measurements, also takes into account variations in land use and the presence of linear landscape elements, which modify runoff and soil redistribution processes and sediment connectivity along the toposequences. The results show that erosion predominated on the steep cultivated slopes, but lower soil redistribution rates were found on the uncultivated slopes. On the flat areas at the bottom of both transects, deposition was dominant. Variations in land use and the presence of linear landscape elements control soil redistribution processes. Such elements can perform the role of Ecological Focus Areas (EFAs), proposed within ‘The Green’ Common Agricultural Policy for 2014, in which at least 7% of a farmerʹs land should comprise EFAs, which can include terraces, landscape features, buffer strips and afforested areas.