Temporal and material variability of podzolization processes

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Podzols of temperate and higher latitude are characterized by translocation of dissolved and particulate organic and inorganic substances from the topsoil into the subsoil. A comprehensive theory on the formation and development of Podzols is still missing, in spite of intensive research for decades. The proposed project aims at systematically reassessing of mobilization and immobilization processes. The objective of the proposed project is to obtain a comprehensive and integrative process-related understanding of the physical and chemical mechanisms that control the formation and development of Podzols. The main hypothesis to achieve the objective is that podzolization consists of an interplay of physical and chemical processes that act variably as a function of time and of the composition of soils. To test this main hypothesis, soils with varying degrees of podzolization (five soils, from an acidic Cambisol to a Haplic Podzol) will be studied in a combination of classical soil analysis, spectroscopic analyses, an experimental pedological approach and geochemical modelling. The soils to be studied will be characterized with soil-science methods (amongst others pH, texture, CEC, contents of oxides etc.). The topsoils will be irrigated with artificial rain water in column experiments to characterize the discharge of dissolved and particulate substances quantitatively and qualitatively. The data will be evaluated with the NICA-Donnan model to estimate metal-organic complexation. Additionally, organic and inorganic particles will be collected in situ in the field and subsequently analyzed by infrared and nuclear-magnetic-resonance spectroscopy together with nano secondary ion mass spectrometry (NanoSIMS). To study the formation of E horizons, the (E)Ah horizon of a Cambisol, showing signs of initial podzolization, will be irrigated with diluted acetic acid to analyze discharged dissolved and particulate substances again quantitatively and qualitatively. Column experiments with mineral mixtures (quartz, variably exchanged illite, ferrihydrite) and a forest-floor extract will be carried out to check immobilization processes. Organo-mineral associations that will have formed will be studied by infrared spectroscopy. Minerals, having reacted with organic matter, will be analyzed at the sub-micron scale by NanoSIMS. Finally, immobilization of organic matter in Podzol subsoils will be quantified and spectroscopically qualified after physical fractionation of B horizons, origination from soils with variable degree of podzolization. The findings of this project will deepen the understanding on the formation, the properties and the dynamics of Podzols and the elements (C, N, Fe, Si, Al, Mn) involved, which take part in global element cycles.