Importance of land use patterns for erosion-induced carbon fluxes in a Mediterranean catchment

Land use and land cover (LULC) have a strong influence on the intensity of soil erosion processes and the consequent loss of soil organic carbon (C) and nutrients from soils. Yet, at the landscape scale most studies quantifying the effect of soil erosion on soil C dynamics have focused on homogeneous (mainly agricultural) areas. Here we study the effect of LULC patterns on erosion-induced lateral C fluxes and the net ecosystem C balance at the catchment level. The SPEROS-C model, a soil erosion model coupled with a C dynamics model, was applied to 12 catchments ranging from 8 to 430 ha in SE Spain and calibrated with field-based data on sediment yield and soil C concentration. Four LULC classes were considered: forest, shrubland, pasture and agriculture. Agricultural areas were the most dynamic sites accounting for 70% of the eroded soil but only for 45% of the total eroded C. The remaining percentage of eroded C derived mainly from relatively C rich forest soils which were the dominant LULC class in terms of spatial extent. The impact of soil erosion on annual ecosystem C fluxes was highest for agricultural soils due to lower C input and soil C stocks. During the study period (28 years), 26% of the eroded C remained within the catchments' hillslopes deposited in 6% of the hillslope area, and not homogeneously distributed over the landscape. These results indicate that assessment of the role of soil erosion on soil C dynamics and ecosystem C fluxes should be undertaken from a landscape perspective, including the effects of LULC on the redistribution of erosion-induced C fluxes.