Capturing relevance and triggers of lateral subsurface flow occurrence in heterogeneous agricultural hillslope soils (LASSO)

• Applicant: Dr. Annelie Ehrhardt
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 531951303

Lateral subsurface flow (LSF) is a ubiquitous phenomenon along impeding layers in agricultural hillslopes leading to enhanced pesticide and nutrient transport. Especially, in heterogeneous hillslope soils, like the soils of the hummocky ground moraines covering vast areas in northern Germany, it remains it remains unknown when and how often this phenomenon occurs. In contrast to forested landscapes, where LSF has been frequently examined, knowledge about triggers and relevant pathways for LSF in agricultural landscapes is still limited. To analyse when LSF occurs and what conditions might cause LSF, wavelet analysis, principal component analysis and the soil water mass balance method are applied to a data set of water content time series measured in lysimeters and corresponding field profiles at the CarboZALF experimental site in in Dedelow (northeast Germany). Triggers causing LSF are identified by statistical analysis of LSF events. To test whether plant roots are relevant pathways for LSF, rectangular soil samples along the impeding plough layer are taken and flow patterns are analysed by isotopic analysis and numerical modelling. In a field tracer experiment it is analysed whether LSF occurs rather in sand lenses or sand bands in the presence of both structures in hillslope soils. Therefore, a bromide tracer is applied and the propagation of the tracer plume is monitored by electrical resistivity (ERT) measurements. The findings will contribute to an enhanced process understanding and assessment of transit times and pathways of pesticide and nutrient transport in hummocky agricultural landscapes. The question will be answered whether LSF is a relevant phenomenon for subsurface water dynamics in the heterogeneous soils of agricultural hillslopes.

• DFG Programme: Research Grants