The imprint of hydroclimate, urbanization and catchment connectivity on the stable isotope dynamics of a large river in Berlin, Germany

Funding Information: This study was funded through the German Research Foundation (DFG) as part of the Research Training Group “Urban Water Interfaces” (UWI; GRK2032/2) and the Einstein Foundation as part of the “Modelling surface and groundwater with isotopes in urban catchments” (MOSAIC) project. Funding was also received through the Einstein Research Unit “Climate and Water under Change“ from the Einstein Foundation Berlin and Berlin University Alliance. We thank all colleagues involved in the daily precipitation and weekly stream water sampling, in particular Esther Brakkee, Jan Christopher, Adrian Dahlmann, David Dubbert, Larissa Lachmann and Anna Wieland. Esther Brakkee is further thanked for participating in the soil SUEO sampling and contributing samples from the wider area around the site. We also thank David Dubbert for running the isotope analysis and Hauke Dämpfling for maintaining the field installations at the SUEO. Aaron Smith is thanked for his help with the data analysis. Finally, we thank the Berlin Senate Department for the Environment, Transport and Climate Protection for supporting this project and providing the data needed to put our results into a wider perspective.Peer reviewedPublisher PD

Using soil water isotopes to infer the influence of contrasting urban green space on ecohydrological partitioning

Acknowledgements We thank the German Research Foundation (DFG) for funding this project as part of the Research Training Group “Urban Water Interfaces (UWI)” (GRK 2032/2) and the Einstein Foundation for the support as part of the project “Modelling surface and groundwater with isotopes in urban catchments (MOSAIC)”. We are especially thankful to our colleagues of the TU Berlin Ecology Department for providing access to their property and assistance for site selection, in particular Birgit Seitz, and to the Department of Climatology, especially Dieter Scherer and Fred Meier, for providing the UCO climate data. Further, we thank our colleagues Esther Brakkee, Larissa Lachmann, Nina-Sophie Weiß, Christian Marx, Lukas Kleine, Wiebke Lehmann, Hauke Dämpfling, David Dubbert, Anna Wieland, Jonas Freymüller, Sylvia Jordan and Mikael Gillefalk for assistance in the sampling and installation of equipment and David Dubbert for help with the isotope analysis. Finally, we thank the Berlin Senate Department for the Environment, Transport and Climate Protection for providing groundwater data and well access. Financial support This research has been funded by the Deutsche Forschungsgemeinschaft (grant no. GRK 2032/2). The publication of this article was funded by the Open Access Fund of the Leibniz Association.Peer reviewedPublisher PD

Quantifying the effects of urban green space on water partitioning and ages using an isotope-based ecohydrological model

Funding Information: Einstein Stiftung Berlin (grant no. EVF-2018-425), the Deutsche Forschungsgemeinschaft (grant no. GRK 2032/2), the Bundesmin-isterium für Bildung und Forschung (grant no. 01LP1602) and the Leverhulme Trust (grant no. RPG-2018-375). This open-access publication was funded by Technische Universität Berlin. Acknowledgements. The authors wish to thank the Einstein Foundation for financing the MOSAIC project, in which this study was performed. Contributions from Chris Soulsby were also funded by the Leverhulme Trust’s ISOLAND project. The German Federal Ministry of Education and Research (BMBF) funded instrumentation of the Urban Climate Observatory (UCO) Berlin under grant 01LP1602 within the framework of Research for Sustainable Development (FONA; https://www.fona.de, last access: 21 June 2021). We also acknowledge support by the German Research Foundation and the Open Access Publication Fund of TU Berlin. The majority of the simulations were performed on the High Performance Computing cluster of TU Berlin. We thank Christian Marx for regular input during the modelling process, Lukas Kleine for help with figures and Ralf Duda for indispensable help with technical issues throughout the modelling process.Peer reviewedPublisher PD

Using stable isotopes for multi-scale assessment of ecohydrology in drought-affected urban water systems

In vielen Städten erfordern fortschreitende Urbanisierung und Klimaerwärmung ein besseres Verständnis des urbanen Wasserkreislaufes zur Entwicklung nachhaltiger Wassernutzungskonzepte. Jedoch erschwert die Komplexität urbaner Wasserflüsse die Nutzung hydrologischer Tracer. In dieser Arbeit werden stabile Isotope des Wassers, hydrochemische und -klimatische Daten genutzt, um die Wasserverteilung und -speicherung in Berlin in den Trockenjahren 2018–2020 zu untersuchen. Auf kleinräumiger Skala wurden Unterschiede bei Evapotranspiration, unterirdischen Fließwegen und Wasserspeicherung unter urbanen Grasflächen, Sträuchern und Bäumen deutlich. Im peri-urbanen Fluss Erpe erschwerte die geringe Variabilität von Abfluss- und Isotopendynamiken die Bestimmung von Verweilzeiten und Mischprozessen. Während warmer, trockener Sommer führte ein hoher Klarwasseranteil zu einer Verschlechterung der Wasserqualität. Auf der stadtweiten Skala wurde der Einfluss von Grundwasser, Niederschlag und Abwasser auf verschiedene Flüsse untersucht. Große Variabilität der Isotopendynamiken wurde in Einzugsgebieten mit Flächenversiegelung und Regenwassereinleitung beobachtet. Die Anreicherung schwerer Isotope in Spree und Havel im Sommer und Herbst verdeutlichte den Einfluss von großskaligen Klimadynamiken und Verdunstung im stromaufwärts gelegenen Einzugsgebiet. Ein nachhaltiges Management urbaner Grünflächen sowie die Speicherung von Regenwasser können dazu beitragen, den Einfluss von Klimaänderungen auf Berlins Wasserressourcen auf lokaler Ebene abzumindern. Jedoch werden großskalige Nutzungskonzepte in den Einzugsgebieten der Spree und Havel benötigt, um Wasserverluste zu minimieren und Abflussraten aufrecht zu erhalten. Weiterführende isotopenbasierte Studien haben großes Potential, das Verständnis von Wasseralter, Abflussentstehung, Verdunstung und langfristigen Dürrefolgen, sowie der Übertragbarkeit der Erkenntnisse auf andere Metropolenregionen, weiter zu verbessern.In urban areas, progressing urbanisation and climate warming call for a comprehensive understanding of urban water cycling to establish sustainable water management strategies. However, the complexity of urban water fluxes complicates the application of hydrological tracers. This thesis used stable isotopes of water, combined with hydrochemical and climatic data, to characterise water partitioning and storage in Berlin, Germany, during the exceptionally warm and dry 2018–2020 period. At the plot-scale, differences in evapotranspiration, subsurface flow paths and storage under urban grassland, shrub and trees were evident. In the peri-urban river Erpe, low variability in discharge and isotopic dynamics limited the applicability of transit time and end member mixing approaches. During warm and dry summers, high contributions of treated wastewater effluents caused a deterioration of water quality. At the city-scale, contributions of groundwater, storm runoff and effluents to different local streams were studied. Isotope dynamics were most variable in catchments with high levels of imperviousness and connectivity to storm drains. In the Spree and Havel rivers, the isotopic enrichment in summer and autumn reflected the impact of large-scale climate dynamics and evaporative losses in the upstream catchment. To mitigate climate change impacts on Berlin’s water resources in the future, the sustainable management of urban green spaces and better capturing of urban rainfall may limit water consumption at the local scale. However, maintaining discharge in the Spree and Havel rivers during warm and dry periods will require catchment-scale management practices that limit water consumption and losses in upstream areas. Future isotope-based research in urban areas has great potential to improve the understanding of urban water ages, source contributions to urban streamflow, evaporation and long-term drought recovery, as well as upscaling the results to other metropolitan areas