CODE RED: Comprehensive demystification of water redistribution in the subsurface with geophysical and water isotope experiments

• Applicants: Dr.-Ing. Matthias Beyer; Professor Dr. Matthias Bücker
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Soil Sciences ; Forestry ; Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography ; Ecology and Biodiversity of Plants and Ecosystems ; Plant Physiology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 583572060

The objective of this project is to study water redistribution processes in the soil through a targeted field experiment using geophysical methods and stable water isotope approaches. A primary focus is on measuring and quantifying the nocturnal redistribution of water via plant roots—hydraulic redistribution (HR). Although this process has been frequently observed and demonstrated in laboratory and seedling studies, its ecological significance has remained largely unclear because it has simply not been possible to measure HR at larger spatial scales. In preliminary experiments conducted in a European forest ecosystem and in an urban ecosystem, we succeeded for the first time in measuring this process across larger areas under real-world conditions. To achieve this, we used geophysical measurements (ERT) specifically adapted for detecting subtle changes in soil water content and for continuous monitoring. These measurements were complemented by stable water isotope approaches and ecohydrological techniques. In the urban ecosystem, this combined approach allowed us to clearly identify nocturnal redistribution processes: during the observation period, substantial nighttime water movement toward the trees’ root zones occurred. The proposed project aims to repeat and further evaluate this combined geophysical–isotope approach in a tropical dry forest, thereby testing its suitability under markedly different environmental conditions. At the planned field site, deep rooting has already been documented, and during the dry season, soil and atmospheric gradients are considerably stronger. If the methodology proves successful, it would mark a major breakthrough in understanding HR at larger scales—after several decades of research into its ecological relevance. The overarching goals of the project are therefore to measure and quantify HR at both point and plot scales, and to unambiguously demonstrate that the observed water movement results from HR rather than transport through the soil matrix. The methodological framework proposed here will enable this distinction.

• DFG Programme: Research Grants