Interplay between soil formation and geomorphic processes along a soil catena in a Mediterranean mountain landscape: an integrated pedological and geophysical approach

Soil spatial distribution often shows high variability because of geo-environmental settings affecting soil formation and geomorphic processes. The paper describes a combined pedological–geophysical approach for investigating the interplay among soil-forming processes, geomorphic dynamics and physico-chemical soil properties in a soil catena in a Mediterranean mountain landscape (southern Italy). Stocks of soil organic carbon (SOC) and total nitrogen (STN) were determined and their interactions with slope position analyzed. Five slope units were defined along the soil catena (summit, shoulder, back, foot, and toe slopes), and in each of them, a soil profile was dug and analyzed. Thickness of soil horizons and contact between soil and parent material were determined by a 2D-electrical resistivity tomography survey. Results showed granitic bedrock is characterized by vary weathering degrees strongly affecting soil type development. Moreover, soil properties variation is related to topographic features and water erosion processes. Soil chemical composition showed high values of SiO2 and Al2O3, probably due to inheritance from underlying granitic parent material. Particularly, Fe2O3 content increased with weathering conditions as shown by chemical index of alteration values. Along foot and toe slopes, reworking and accumulation of colluvial soil lead to the formation of thicker accretionary A horizon. Consequently, summit areas, together with foot and toe slopes had greater SOC and STN stocks than back and shoulder slopes. That because soils are thicker and richer in SOC on summit and valley bottom than in shoulder and back-slope positions. The proposed approach has showed the benefit of an integrated methodology for investigating spatial variations along soil catenas.