Concurrent evolution of organic and mineral components during initial soil development after retreat of the Damma glacier, Switzerland

Abstract

The foreland of the Damma glacier (Switzerland) was investigated to assess the build-up of organic carbon (OC) stocks in mineral soils and organic surface layers with increasing ice-free period (ca. 15, 60–70, 71–80 and 110–140 years). Mature soils outside the proglacial area (soil ages > 700 years) served as reference for advanced soil development. All soils were sampled in triplicate per surface age to estimate the variability of soil formation. Different selective dissolution methods were applied to quantify Fe and Al pools with respect to their role for soil organic carbon (SOC) stabilization during initial pedogenesis. The chemical composition of organic matter was characterized by using solid-state CPMAS 13 C NMR spectroscopy. Leptosols and Regosols were found in the glacier foreland which showed a high variability of development ranging from morphologically undeveloped to soils forming Ah horizons within 70 years. These different stages of soil development were present at a small scale within the same surface age according to past glacier movements. Particle-size distribution varied between soils of similar age and without chronological trend. These results point to the strong impact of different glacial deposition and subsequent glaciofluvial erosion, which was indicated by buried organic surface layers, on soil formation. In general, we found a rapid accumulation of OC in the mineral soils (7.1 g m −2 year −1) and organic surface layers with increasing soil age. Similarly, the amount of poorly crystalline Fe oxides and Al phases increased reflecting the growing potential for SOC stabilization. This was indicated by the strong relationship between SOC stocks and stocks of oxalate soluble Fe and Al. In contrast to strongly increasing quantities, only small changes in the composition of organic matter as well as Fe and Al pools were detected during initial pedogenesis. Fe oxides and inorganic Al phases mainly remained poorly crystalline. Our results point to the concurrent evolution of SOC and poorly crystalline Fe oxides and Al phases with positive feedback mechanisms during initial soil formation. In the Swiss Alpine environment, soil development on silica rich parent material proceeds to Cambisols within at least 700 years as evidenced by the reference soils found outside the proglacial area. They showed indications of weak podzolization as some Fe and Al were translocated downwards. The comparison between the foreland soils and the Cambisols showed decreasing accumulation rates of SOC and pedogenic Fe and Al. This indicates that soil formation processes slow down already after some hundred years or accumulation of Fe and Al increasingly occurs at greater soil depth.