Dyes are useful tracers to stain the flow pathways of water and solutes in the vadose zone.
The application of dyes to the soil surface and the subsequent excavation and examination of the trench face reveals a detailed picture of the often highly irregular flow patterns encountered in porous media, in a spatial resolution that currently no other sampling technique can achieve. The aim of this project is to systematically evaluate and examine dyes suitable as tracers for staining purposes in the vadose zone. Selected compounds will be tested in a laboratory screening test for their suitability as tracers. Promising candidates from the screening test will then be subject to an elaborate laboratory investigation of tracer characteristics, such as batch and column sorption measurements, and influence of solution chemistry on emission spectra, as well as on sorption and transport through soil. We anticipate that as a result of this project we can recommend several dyes suitable as tracers in the three mobility categories.