Soils chronosequences in high-altitude environments: the case of Alpe Veglia (Lepontine Alps)

Climate change has a huge impact on alpine environments. In high altitude environments, one of its most visible effects is glaciers retreat, which causes the progressive exposure of previously glaciated surfaces, where weathering processes promote soil formation. These areas are open-air laboratories where, substituting space for time, the effect of time factor on soil development can be isolated from the effect of the other soil-forming factors (Egli et al., 2006). However, isolating the effect of time from the other factors could be challenging when considering the high geomorphic activity featuring proglacial areas, where paraglacial dynamics are expected to control landscape changes and sediment supply even limiting the vegetation establishment (Temme et al., 2016). The aim of our study is to evaluate soil evolution along a soil chronosequence in the Alpe Veglia area (Lepontine Alps). We performed a field and laboratory characterization of seven soil profiles sampled on different time-exposed surfaces, from the Aurona glacier proglacial area to the Alpe Veglia plain across different age glacial deposits. Our preliminary results suggest major evidences of differentiation between younger soils of the proglacial area and the well-developed soils outside it, on Pleistocene-aged deposits. The results of physical and chemical analyses underline a time-trend of soil skeleton concentration, fine particles fraction, accumulation of soil organic carbon and acidification. On the other hand, some soil profiles developed outside the proglacial area s.s. do not show the same trend with time in their properties. In particular, two profiles deviate from the trend with a higher amount of clay and organic matter with respect of older profile, while another profile shows an unusual abundance of gravel in the surface horizon with slightly higher pH values. Hence, various soil forming factors might have induced a divergence from the chronosequence, probably depending on both the lithological heterogeneity of glacial deposits (calcschists, gneisses, prasinites) and the influence of different geomorphic dynamics such as surface processes. Moreover, differences in aspect and micro-climatological conditions may need to be considered. Our results demonstrate that soil properties variability along the chronosequence can be mainly explained according to the soil-chronosequence approach, but other factors need to be considered in order to better evaluate how the landscape changes in such a sensitive and dynamic environment.