Controlled column experiments under unsaturated conditions

To study the transport behavior of conservative tracers and reactive substances in repacked and undisturbed soil columns under unsaturated conditions, a fully automated soil column setup was developed. A pump provides the constant or time-variable water flux and water is applied to the soil surface by 19 needles. A controlled suction, operated in the range of 0 to -70 hPa, can be applied to the lower boundary. The soil columns are equipped with two tensiometers to check unit gradient conditions. Before the effluent is collected in a sampling collector, it can optionally be directed through a conductivity cell to measure the bulk electrical conductivity on-line (breakthrough curve for salt tracers) and through a photometer to measure the absorbance on-line (breakthrough curve for a dye tracer). Control of the boundary conditions and the data acquisition is fully automated. Currently, three soil columns can be operated using this set up. The measured breakthrough curves and concentration profiles reveal information on sorption, degradation, and kinetic processes at the column scale. Additionally, radioactive labeled substances (e.g. 14C labeling of pesticides or xenobiotics) can be used in the column experiments due to its location within a radioactive laboratory.