Quantification of active interfaces with respect to dissolved chemicals in unsaturated structured soil

Principal investigator: Prof. Dr. H.-J. Vogel

Co-worker: Dr. J.M. Köhne


Goals
The main goal is to develop a new methodological approach to quantify the effect of soil structure on fluid dynamics and interaction of dissolved chemicals in natural soil at the scale of a soil horizon. The conceptual perspective is that of a particle and what it 'sees' on its way through soil.
The approach is based on high resolution X-ray tomography of natural structured soil samples with a typical dimension of 10−1 m and a spatial resolution down to 10−5 m.
By establishing a direct link between observable soil structure and soil functions with regard to flow and transport, the project aims at opening new perspectives for the predictive modelling of chemical displacement in soil.

Hypotheses
A key for the understanding of chemical interactions is the intensity of the contact between soil/pore interfaces and the chemical. The main soil properties affecting the fate of reactive chemicals released to soils are (i) the quality and spatial arrangement of organic and inorganic soil constituents (the biogeochemical interfaces), (ii) the spatial arrangement of void space (the porous structure), and (iii) the variable water content which determines the heterogeneous velocity field of soil water.

The structure analysis is expected to provide essential structure-dependent parameters that can be used for modelling chemical interaction and transport of sorbing and non-sorbing solutes.

Scientific Approach
• Quantification of pore-solid interfaces in undisturbed structured soil samples using X-ray micro-tomography
• Application of mathematical morphology tools to obtain 'structure-measures' including the size distribution of pores (> 0.01 mm), their interfacial area and topology, and evaluation of the concept of local percolation probabilities for quantification of the pore connectivity
• Representation of the porous structure through an equivalent network model and numerical simulation of flow and transport at various water contents including transient conditions.
• Calculation of the potential interaction between dissolved chemicals and the pore-solid interfaces based on particle tracking and solute transport simulations within the network model.
• Demonstration of the predictive power of our approach through experimental breakthrough curves for conservative and interacting solutes.

Cooperation within the priority programme
Prof. Dr. J. Bachmann, PD Dr. T. Baumann


Vogel

Soil aggregate (diameter 10 mm) with pores larger than 0.01 mm.

Red pores are airfilled and blue pores are water filled as an example

of complex interfaces at a simulated water potential of 30 hPa. Quartz grains are yellow.

Poster Vogel