Spodosol-Histosol evolution in the Krkonose National Park (CZ)

Podzols often occur in association with organic soils along sequences governed by relief, with peats in depressions and podzols on slopes. The formation of bogs has also been described as a soil-induced process: the formation of cemented pans, impermeable to water, in highly developed podzols, enhanced the accumulation of organic matter and slowed down its decomposition. Humans may interfere with soil development, enhancing acidification and thus the eluvial phase of podzolisation, as it may be in the case of acid precipitation or of the plantation of conifers. The aim of this work was to study the transition between Spodosols and Histosols, in the Krkonosˇe National Park (CZ), where spruce has substituted the natural vegetation and acid precipitation has damaged several areas of the park. The soils were studied at two sites: one site is relatively preserved and soils (Spodosols and Inceptisols) develop on a steep slope. At the other site, a gently undulating mountain summit, Spodosols are associated to Histosols and the forest decline is more severe. Three Spodosols (Humic Haplocryod, Typic Cryaquod, Placic Cryaquod) and a Histosol were selected at the second site, and the soil properties and organic matter dynamics were compared to those of a Typic Haplocryod sampled at the first site. Profile morphology and chemical analyses indicated that podzolisation has been more intense at the second site, probably because of the differences in relief and in the amount of water available for pedogenic processes: a high accumulation of organic matter and thick Bhs horizons were the most striking differences, together with depletion in Fe from eluvial horizons. Moreover a trend in the chemical indicators of podzolisation was appreciated among the profiles sampled at the second site. The analyses of organic matter and humic substances indicated that, in Bs horizons, the organic matter characteristics were very similar in the two sites, but in the eluvial and organic horizons marked differences appeared. At the first site, the fulvic acids in the E horizons were small and oxidised, similar therefore to those found in the Bhs horizons, whereas at the second site fulvic acids became bigger, more aliphatic and less oxidised and were therefore less prone to migration. Some of these properties of organic matter were linked to soil water regime, others to the shift in vegetation from forest to grass cover and seemed therefore to be related to the soil evolution itself, being podzolisation in this sense a self-limiting process. Acid precipitation may however have played a role in the change of size of fulvic acids, which were very rich in sulphur, through C–S linkages. The complex interaction between natural and anthropogenic factors seemed to have decreased the ability of organic matter to migrate, enhancing the formation of Histosols.