Using advances in stable water isotopy to quantify species- and interspecific ecohydrological feedback processes and water transit times of different tree stands

• Applicants: Professorin Natalie Orlowski; Professorin Dr. Christiane Werner
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 444110369

Significant changes in hydrological extreme events are predicted to increase in occurrence and severity in the future. Understanding the complex linkages and interactions between precipitation inputs, water storage in the soil and groundwater, as well as catchment output water fluxes is still a major challenge in ecohydrology. Vegetation plays a pivotal role in the hydrological cycle controlling 50-70 % of terrestrial evapotranspiration. Distinct plant species differ significantly in their water use strategies. Integrating such information on species-specific alterations of soil infiltration, hydraulic redistribution, and root-water uptake dynamics delivers first hints on how trees may funnel water towards their active root zones. This will become important under future climatic conditions and the development of adaptation strategies for a sustainable forest ecosystem management.The concept of water ages by means of water isotopes is used to assess how different flow paths contribute to runoff and how these contributions change over time. Water ages provide a different dimension in addition to hydrometric responses, helping to better understand the hydrological processes and improve the realism of hydrological models. This concept mostly has been used to focus on individual compartments of the (eco-)hydrological cycle or the whole catchment. However, recent developments in transit time estimations, demonstrate that we need to consider the interfaces among the compartments (e.g., soil-atmosphere or soil-roots) for a more holistic understanding of the ecohydrological cycle. Therefore, species-specific differences and complementary resource utilization of trees in mixed stands might alter water transit times and ages in the ecohydrological cycle.Our central hypothesis is that species identity and water competition between tree species is a major driver for ecohydrological soil-tree feedback processes. We will investigate our central hypothesis on pure and mixed stands of fir and beech trees in a combined experimental (work packages (WPs) 1-3) and modelling approach (WP 4), where high spatial resolution of isotopic, hydrometric, classical and novel plant eco-physiological measurements will be combined with continuous long-term monitoring to quantify all compartments of the ecosystem’s water cycle. Isotopic signatures of water fluxes and pools on a natural abundance level will be observed via a novel in-situ isotope monitoring platform (SWIP) for one year (WP 1) to validate the SWIP system for the specific tree species and soil types. In WP 2, we will conduct an isotope labelling experiment to quantify stand specific temporal heterogeneity of the ecosystem compartment’s response times. WP 3 will focus on unravelling transit times and water ages of the distinct ecosystem compartments. In WP 4, we will apply the acquired data to model ecohydrological processes using SWIS. We will improve and adapt the model structure to the different tree stands.

• DFG Programme: Research Grants
• International Connection: Canada
• Major Instrumentation: Cavity Ring-down Spectrometer
• Instrumentation Group: 1860 Spezielle Spektrographen und Spektrometer
• Co-Investigators: Dr. Maren Dubbert; Professor Dr. Markus Weiler
• Cooperation Partner: Professor Dr. Jeffrey J. McDonnell