Warter et al. (2025) Assessing the sensitivity of urban aquatic nature-based solutions to hydroclimate variability using stable water isotopes

Identification

• Journal: Environmental Monitoring and Assessment
• Year: 2025
• Date: 2025-12-06
• Authors: Maria Magdalena Warter, Chris Soulsby, Kati Vierikko, Silvia Martín Muñoz, Daniel Gebler, Mariusz Sojka, Vladimíra Dekan Carreira, Cristina Antunes, Pedro Pinho, Doerthe Tetzlaff
• DOI: 10.1007/s10661-025-14882-x

Research Groups

• Department of Ecohydrology and Biogeochemistry, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
• Northern Rivers Institute, University of Aberdeen, Scotland.
• Chair of Water Resources Management and Modeling of Hydrosystems, Technical University Berlin, Germany.
• Built Environment Solutions Unit, Finnish Environment Institute (SYKE), Helsinki, Finland.
• ECOSPHERE Research Group, Department of Biology, University of Antwerp, Belgium.
• Department of Ecology and Environmental Protection & Department of Land Improvement, Poznań University of Life Sciences, Poland.
• Center for Ecology, Evolution and Environmental Changes (cE3c) & CHANGE Institute, Faculty of Sciences, University of Lisbon, Portugal.
• Department of Geography, Humboldt University of Berlin, Germany.

Short Summary

This study utilizes stable water isotopes ($\delta^{18}O$ and $\delta^{2}H$) to characterize the hydrological functioning and hydroclimatic sensitivity of urban aquatic nature-based solutions (aquaNBS) across four European cities. The findings reveal that pond-based systems are highly sensitive to recent precipitation and evaporation, while stream-based systems exhibit greater resilience due to the mixing of older water sources and groundwater.

Objective

• To identify dominant water sources and flow paths in urban aquaNBS (streams and ponds) across a continental hydroclimate gradient in Europe.
• To estimate water residence times using transit time proxies (young water fractions and damping ratios) from low-frequency isotope data.
• To evaluate the utility of tracer-based diagnostics for monitoring the sensitivity of blue infrastructure to future hydroclimatic variability.

Study Configuration

• Spatial Scale: Four European cities representing diverse climates: Poznań, Poland (Continental/Oceanic); Berlin, Germany (Continental); Antwerp, Belgium (Oceanic); and Lisbon, Portugal (Mediterranean). A total of 48 sampling locations were included.
• Temporal Scale: Seasonal grab sampling conducted over a one-year period between February 2023 and March 2024, supplemented by monthly sampling at selected sites in Berlin.

Methodology and Data

• Models and Proxies:
  • Transit Time Proxies (TTP): Damping Ratio (DR) and Young Water Fraction ($F{yw}$), where $F{yw}$ represents water less than ~3 months old.
  • Isotopic Analysis: Linear least squares regression to define Local Meteoric Water Lines (LMWL) and Local Evaporation Lines (LEL); calculation of deuterium excess (d-excess) and line-conditioned excess (lc-excess).
• Data Sources:
  • Field Samples: Seasonal and monthly grab samples of surface water.
  • Isotopes: Global Network of Isotopes in Precipitation (GNIP) database for historic precipitation signatures.
  • Hydroclimate: Daily precipitation, air temperature, and relative humidity from national weather services (DWD, SNIRH, IMGW-PIB, and Vlaanderen).
• Instrumentation: Picarro L2130-i cavity ring-down water isotope analyzer.

Main Results

• System Sensitivity: Ponds showed higher sensitivity to hydroclimate changes, characterized by strong seasonal evaporative enrichment and high young water fractions (mean $F{yw} \approx 0.65$). In Antwerp, pond water was almost entirely composed of recent precipitation ($F{yw} > 0.9$).
• System Resilience: Streams generally indicated longer transit times and greater mixing with older water sources (mean $F_{yw} \approx 0.3$), suggesting higher resilience to short-term hydroclimatic fluctuations.
• Evaporative Fractionation: Significant enrichment was observed in Berlin and Antwerp during summer, with d-excess values dropping as low as $-14.3\text{‰}$ and $-23.9\text{‰}$, respectively.
• Sampling Efficiency: Comparison in Berlin demonstrated that seasonal sampling (4 times/year) provided broad hydrological characterizations comparable to monthly sampling, though monthly data better captured the high-frequency variability in rapidly responding ponds.

Contributions

• Provides the first multi-city comparative assessment of aquaNBS hydrological functioning using stable isotopes across a European climate gradient.
• Demonstrates that low-frequency isotope sampling is a viable, cost-effective monitoring tool for characterizing urban blue infrastructure in data-scarce environments.
• Establishes an evidence base for the "urban stream syndrome" and the vulnerability of stagnant, single-source urban ponds to eutrophication and water loss under projected climate warming.

Funding

• BiodivRestore ERA-NET Cofund (GA No 101003777) via the 2020–2021 Biodiversa and Water JPI joint call.
• German Ministry of Education and Research (BMBF) (Grant No. 16WL015).
• German Research Foundation (DFG) (Research Training Group GRK2032/2).
• National Science Centre Poland (UMO-2021/03/Y/NZ8/00100).
• Fundação para a Ciência e a Tecnologia (FCT), Portugal (2020.03415.CEECIND/CP1595/CT0006, DivRestore/0001/2020, 2022.08532.CEECIND/CP1715/CT0006).
• Einstein Stiftung Berlin (MOSAIC project EVF-2018–425).
• Kurt Eberhard Bode Stiftung and Rüdiger Kurt Bode Stiftung.

Citation

@article{Warter2025Assessing,
  author = {Warter, Maria Magdalena and Soulsby, Chris and Vierikko, Kati and Muñoz, Silvia Martín and Gebler, Daniel and Sojka, Mariusz and Carreira, Vladimíra Dekan and Antunes, Cristina and Pinho, Pedro and Tetzlaff, Doerthe},
  title = {Assessing the sensitivity of urban aquatic nature-based solutions to hydroclimate variability using stable water isotopes},
  journal = {Environmental Monitoring and Assessment},
  year = {2025},
  doi = {10.1007/s10661-025-14882-x},
  url = {https://doi.org/10.1007/s10661-025-14882-x}
}

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