A profile within the Upper Freshwater Molasse (OSM) of eastern Switzerland was sampled. Particle-size analyses, bulk chemical analyses, cation exchange capacities and Fe fractions (oxalate- and dithionite-citrate-bicarbonate-soluble Fe, total Fe) were measured. The mineralogical composition was determined by X-ray diffraction and quantified with Rietveld analysis. The layer charge of selected fine-clay samples was determined with the alkylammonium method using chain nc = 12. The profile could be divided into a lower sequence (I) and an upper sequence (II) by a hiatus. Chemical data, particle-size distributions and calcite contents indicated that soil formation was essentially restricted to wetting-drying cycles associated with redox cycles evident from Feo/Fed and Fed/Fet ratios. A significant correlation between the d060 values of the dioctahedral smectite-illite mixed-layer phases and Feo/Fed was interpreted as the influence of microbial Fe3+ reduction, which affected both the Fe oxides and Fe-rich clay minerals. This is the first evidence that the Fe dynamics of both mineral groups may be linked. The amount of illitization also correlated with Feo/Fed, but only in the upper part of the profile. This indicates that wetting-drying cycles were necessary for the illitization process.

Reactive-transport models contribute significantly to the field of modern geosciences. A general mathematical approach to solving models of complex biogeochemical systems is introduced. It is argued that even though mathematical models for reactive-transport simulations can be developed at various levels of approximation, the approach for their construction and application to the various compartments of the hydrosphere is fundamentally the same. The workings of coupled transport-reaction systems are described in more detail by means of examples, which demonstrate the similarities in the approach. Three models of the carbon dynamics in redox-stratified environments are compared: porous media flow problems in a coastal sediment and in a contaminated groundwater system; and a surface flow problem in a eutrophic estuary. Considering the interdisciplinary nature of such models, a Knowledge Base System for biogeochemical processes is proposed. Incorporation of the proposed knowledge base in an appropriate modeling framework, such as the Biogeochemical Reaction Network Simulator, proves an effective approach to the modeling of complex natural systems. This methodology allows for construction of multi-component reactive-transport models applicable to a wide range of problems of interest to the geoscientist.