Soil redistribution, weathering and soil organic carbon dynamics in a Mediterranean landscape

Due to climate change and intense land use, soils are highly dynamic in Mediterranean regions. Soil redistribution rates (erosion/accumulation) are assumed to be the main factor changing soil evolutional trajectories, weathering and organic carbon dynamics in these landscapes, but their interactions remain poorly understood. Therefore, we investigated soil redistribution rates, weathering state, soil organic carbon dynamics and its chemistry in a Mediterranean area, Corleone, Sicily. Although the soils showed clear signs of degradation and erosion of up to 39 t ha −1 yr −1 , as determined by 239+240 Pu tracing, soil erosion measurement and modelling were made challenging by the vertic characteristics of some soils. With decreasing erosion rates, the soils had a higher amount of oxalate-extractable Fe stocks, more crystalline Fe, a lower (Ca + K)/Ti ratio (as a weathering indicator) or a higher CIA value. The organic C stocks ranged from 7 to 25 kg m −2 (average of 14 kg m −2 ). A major part of organic carbon was stored in the large aggregate fraction (≥63 μm). Soil organic carbon dynamics and quality were strongly linked to the soil redistribution rates. Erosion removed the strongly weathered part of the soil and left behind a younger and fresher soil matrix with a low org. C content, but an organic carbon fraction that was enriched in aliphatic chains and lignin-like compounds having a less mature status. The investigated soils had in general an optimal composition for stabilising and sequestering organic matter, even highly eroded and shallow soils still contained a considerable amount of org. C, which is untypical for Mediterranean areas. • In the planned Geopark of Corleone, soil erosion rates are high with up to 39 t ha −1 yr −1 . • Despite high erosion rates, organic carbon stocks remained astonishingly high with 7–25 kg m −2 . • Most of the organic carbon was stored in the fraction >63 μm. • More mature soil organic matter was accumulated in soils having a lower erosion rates. • A clear correlation exists between soil organic C stocks and erosion rates.