Carbon and nutrients cycles in natural porous media, such as soils or sediments, are strongly determined by the activity of the resident microbial populations since many environmentally relevant reactions are mediated by microorganisms. To predict the evolution of biogeochemical cycles, mathematical expressions that describe the rates at which chemical constituents are consumed and produced are necessary. The present research investigates how biogeochemical transformation rates relate to environmental factors and to the physical structure and hydrology of the local environment. Organic matter degradation plays an important role in nutrient cycling in sediments and soils. Coupled to organic matter oxidation, a sequential reduction of electron acceptors with depth generally proceeds on the basis of theoretical thermodynamic energy yields to microorganisms. We are currently working on testing the hypothesis that potential rates of terminal electron acceptor utilization during anaerobic organic carbon oxidation not only reflect the reactivity of the sedimentary organic matter being degraded but also the nature of the terminal electron acceptor.
Experimental work includes flow-through experiments, with which reaction rates are measured under steady-state conditions. In such systems, the physical integrity of the soil/sediment is preserved and solute flow is controlled, therefore mass-transfer limitations will occur the same way as in natural environments. An application of a reactive transport model allows for recovering kinetic parameters for biogeochemical reactions.