Factors affecting mobility/export of particle-bound stable elements after erosive rainfalls in agroforestry Mediterranean catchments of Aragón (Spain)

Abstract

The composition of sediment fluxes caused by erosion can vary greatly both spatially and temporally, causing different impacts on water bodies. The erosion process is mainly driven by soil and rainfall characteristics as well as land use. The aim of this research is to evaluate the combined effect of these factors in a mountain agroforestry system, analysing the relationship of the sediment composition generated after flooding events with soil and rainfall characteristics and the impact of land use. The analyses were based on data recorded in three catchments with Mediterranean climate. The sediments were collected after 21 seasonal campaigns and their characteristics were assessed taking into account rainfall characteristics and the main land uses in each catchment. The results confirm the differences in soil particle mobilization after high and low intensity events and the higher impact of croplands compared to other dominant land uses. The amount of sediments trapped in the catchment with the largest area of cropland almost doubled sediment collected in the other catchments. Clay and soil organic carbon in the sediments were lower than in the original sources, likely due to the lower content in the soils more susceptible to erosion and the washing out of the finer material by runoff under high amount/intensity precipitation. Differences were observed between catchments and between rainfall events in the export of stable elements, with a general sediment enrichment in Al, Be, B, Cu, Mn, S, Sr and Zn, reaching the highest values for Be, Sr and Zn. The elemental enrichment differed according to rainfall characteristics thus Cu, Zn or Mn were higher after low intensity events, while other elements like Be were enriched after high intensity events. These variable patterns evidence the complex interplay of involved factors and the key role of elemental bounds to particle sizes and organic matter.