Eroded but organic carbon rich: Soil dynamics on glauconitic landscapes of Mediterranean Sicily

The surface of the continental Earth is constantly reworked at different scales of time and space by weathering and erosion. Erosion, although perceived as destructive process, can produce spectacular landscapes giving rise to an outstanding geodiversity. Particularly in southern Mediterranean regions, soils have become highly dynamic owing to climate change and intense land use. Soil redistribution rates (erosion/accumulation) determine soil evolutional trajectories, weathering and organic carbon dynamics in such landscapes. The interaction among these factors, however, remains poorly understood. The area around Corleone (north-western Sicily, Italy), a potential new UNESCO geopark, consists of a worldwide peculiar geological condition, i.e. massive glauconitic calcarenites. We investigated soil erosion rates by using ^239+240Pu as tracer, the weathering state of soils, soil organic carbon dynamics and its chemistry in this area. Although the soils showed clear signs of strong degradation and erosion with up to 39 t ha^-1 yr^-1, org. C stocks remained on a surprisingly high level with 7 to 25 kg C m^-2. 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 and having, therefore, a lower maturity. The investigated soils developed on a parent material that promoted the stabilisation and sequestration of organic matter so that even highly eroded and shallow soils still contained a considerable amount of org. C, which is rather unique for Mediterranean areas. Due to the presence of glauconite, smectite and oxyhydroxides in the parent material, the soils were able to retain a high amount of soil organic carbon. The determination of erosion rates on such soils was, however, challenging, and the major difficulties are discussed. Furthermore, when using ^239+240Pu as a tracer for soil erosion, only point information is usually obtained and an extrapolation to a larger area is difficult or very time and resource consuming. A new, promising procedure will be presented, based on ^239+240Pu, on how to overcome this problem in future and how to extrapolate to a whole catchment area.