Impact of physico-chemical soil properties on erosion features in the Aliano area (Southern Italy)

This study has been carried out on three pairs of clayey-silt slopes, which are examples of typical badlands near Aliano (Southern Italy). These show features of erosion which are common to SE-exposed clayey-silt rocks outcropping in the same area. After mineralogical, geochemical and grain size analyses these slopes were compared with the SE-exposed adjacent ones, having however a different erosive action, and a partially-vegetated covering was found. Pedological analyses show a clear development of soil horizons where the slope is rich in organic matter, and this is wholly consistent with the presence of vegetation. A comparison between the eroded substrates and non-eroded substrates showed that the former have higher (16 m) and lower fractions (16 m). The grain size also distinguishes crusts from substrates, the latter having higher fractions (16 m). As to bulk rock mineralogy, this does not differentiate the eroded from the non-eroded slopes. TDS, pH, SAR and PS are parameters which distinguish the eroded from the non-eroded sides of the slopes. On average, the eroded substrates have pH, SAR and PS values higher than the non-eroded ones. The ESP values of the eroded slopes are slightly higher than those of the non-eroded ones. Up to now the relations between pH, TDS, SAR, PS and ESP have been considered as descriptors of dispersivity. However an improvement can be made regarding the predictability of diagrams (such as ESP-TDS) when taking mineralogical composition into consideration. The crusts are less dispersive than the eroded substrates, and the non-eroded ones show the same feature as crusts. This suggests that the most severely-weathered part of a slope tends to reach a stable condition when a strong decrease in SAR, PS and ESP occurs. This study shows that the erosion mechanism involves morphological and geographic exposure, climatic elements as well as grain size, mineralogy, chemistry and the exchange processes of soil.