Integrative application of geoelectrical methods for the characterization of preferential flow and reactive transport in the vadose soil zone

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Preferential flow phenomena are ubiquitous in unsaturated subsurface environments and have multiple influences on water balance, transport of mobile substances and microbial activity. Quantification and modelling of such phenomena is still difficult and could be greatly improved by geophysical methods. The aim of this proposal is the characterization of preferential flow and its impact on reactive transport in a soil core by means of tomographic geoelectrical methods. In a time variable and unsaturated medium geophysical data interpretation is usually not unique. For instance, infiltrating water, release of ions from the soil and production of carbonates due to microbial activity result in a larger electrical conductivity of the soil core. This non-uniqueness will be reduced by a combination of electrical resistivity, induced polarization and self potential measurements. These methods will be applied in a controlled laboratory environment, because it is assumed that the non-uniqueness can furthermore be reduced by an appropriate selection of boundary conditions and tracers. To be able to characterize one process of influence on a geophysical variable like electrical conductivity, it is necessary to achieve steady state conditions for the remaining processes of influence. This can be done, for example, by varying the flow between steady state and transient regime or with the application of input solutions with different chemical properties, for example solutions, which either inhibit or provoke microbial activity. In this project, the geophysical methods will be supported by lysimeter techniques like frequency domain reflectometry (FDR) probes, tensiometers and a multi-compartment suction plate. The proposed project is innovative as it applies several geoelectrical methods simultaneously in an unsaturated, heterogeneous soil core in combination with time variable but controlled flow boundary conditions.