Unraveling Ecohydrology and Biodiversity in Urban Water Systems: A Multi-Tracer Study of Nature-Based Solutions by Maria M. Warter et al., 2025
In the face of rapid urbanization and climate change, cities are turning to aquatic nature-based solutions (aquaNBSs) such as restored streams and ponds to enhance water security, buffer hydrological extremes, and support biodiversity. However, clear evidence on how these measures influence ecological and hydrological functioning within urban freshwater systems has been limited. This new study by Warter et al. (2025) addresses that gap using an innovative, integrative multi-tracer approach that combines stable water isotopes, hydrochemistry, and environmental DNA (eDNA) to examine ecohydrological dynamics in Berlin’s urban freshwater environments.
Urban water bodies provide crucial ecosystem services—from flood mitigation to habitat provision—but they are often subject to intense anthropogenic pressures such as treated effluent discharge, stormwater runoff, and altered hydrology. These pressures can hinder key ecological processes and constrain biodiversity, yet most evaluations of artificial or restored aquatic ecosystems focus on structural indicators rather than the functional links between hydrology and ecology.
The team conducted monthly sampling across stream and pond sites in Berlin, capturing gradients of urban influence, hydrological variability, and restoration history. By analyzing water isotopes, microbiome compositions, macrophyte diversity, and water chemistry, they were able to:
- Trace water sources and flows using isotope signatures.
- Assess microbial community structure through eDNA metabarcoding.
- Evaluate aquatic plant diversity as an indicator of habitat quality.
This integrative framework allowed the authors to go beyond simple descriptions of water quality and instead explore how urbanization and hydrology shape ecological outcomes in nature-based interventions.
Key Findings
- Urban water sources strongly shape aquatic communities.
Streams receiving treated wastewater showed distinct microbial assemblages dominated by taxa often associated with urban effluent, pointing to limited ecological recovery in these environments. - Urban ponds exhibited low microbial diversity.
Compared to streams, pond microbiomes were less diverse and more sensitive to hydrological fluctuations, highlighting the challenge of sustaining robust ecological communities in small, engineered water bodies. - Macrophyte richness was generally low.
Aquatic plants—critical for habitat complexity and ecosystem functioning—were scarce across both streams and ponds, suggesting that current restoration practices may not sufficiently support plant-mediated ecological pathways. - Restoration alone may not ensure biodiversity gains.
Despite extensive NBS implementation and stream restoration efforts over the past decade, anthropogenic stressors still dominated ecohydrological responses, indicating that structural interventions need stronger ecological integration to achieve biodiversity objectives.
This study emphasizes the value of integrated tracer and biological methods for advancing our understanding of how urban freshwater systems function under multiple stressors. By linking hydrological signatures with biological diversity, the authors highlight critical limitations of many urban aquaNBSs—especially when effluent-dominated flows and simplified habitat conditions prevail.
These insights suggest that future restoration and NBS design should:
- Explicitly consider microbial processes alongside macroecological indicators.
- Prioritize habitat complexity to foster both microbial and plant diversity.
- Recognize the interaction between urban water sources and ecosystem health, not just water quantity metrics.
Ultimately, this research calls for a more holistic, process-based framework for evaluating and designing nature-based solutions in cities—one that bridges hydrology, ecology, and biodiversity at meaningful scales.
Enjoy reading – https://doi.org/10.5194/hess-29-2707-2025
