Societal Drivers of European Water Governance: A Comparison of Urban River Restoration Practices in France and Germany

Wilding cities for biodiversity and people: a transdisciplinary framework

Accelerating urbanisation and associated lifestyle changes result in loss of biodiversity and diminished wellbeing of people through fewer direct interactions and experiences with nature. In this review, we propose the notion of urban wilding (the promotion of autonomous ecological processes that are independent of historical land-use conditions, with minimal direct human maintenance and planting interventions) and investigate its propensity to improve biodiversity and people-nature connections in cities. Through a large interdisciplinary synthesis, we explore the ecological mechanisms through which urban wilding can promote biodiversity in cities, investigate the attitudes and relations of city dwellers towards urban wild spaces, and discuss the integration of urban wilding into the fabric of cities and its governance. We show that favouring assembly spontaneity by reducing planting interventions, and functional spontaneity by limiting maintenance practices, can promote plant diversity and provide ecological resources for numerous organisms at habitat and city scales. These processes could reverse biotic homogenisation, but further studies are needed to understand the effects of wilding on invasive species and their consequences. From a socio-ecological perspective, the attitudes of city dwellers towards spontaneous vegetation are modulated by successional stages, with grassland and woodland stages preferred, but dense shrubby vegetation stages disliked. Wild spaces can diversify physical interactions with nature, and enrich multi-sensory, affective and cognitive experiences of nature in cities. However, some aspects of wild spaces can cause anxiety, feeling unsafe, and the perception of abandonment. These negative attitudes could be mitigated by subtle design and maintenance interventions. While nature has long been thought of as ornamental and instrumental in cities, urban wilding could help to develop relational and intrinsic values of nature in the fabric of cities. Wildness and its singular aesthetics should be combined with cultural norms, resident uses and urban functions to plan and design urban spatial configurations promoting human-non-human cohabitation. For urban wilding to be socially just and adapted to the needs of residents, its implementation should be backed by inclusive governance opening up discussion forums to residents and urban workers. Scientists can support these changes by collaborating with urban actors to design and experiment with new wild spaces promoting biodiversity and wellbeing of people in cities.

Transformative adaptation through nature-based solutions: a comparative case study analysis in China, Italy, and Germany

This paper explores how claims for transformative adaptation toward more equitable and sustainable societies can be assessed. We build on a theoretical framework describing transformative adaptation as it manifests across four core elements of the public-sector adaptation lifecycle: vision, planning, institutional frameworks, and interventions. For each element, we identify characteristics that can help track adaptation as transformative. Our purpose is to identify how governance systems can constrain or support transformative choices and thus enable targeted interventions. We demonstrate and test the usefulness of the framework with reference to three government-led adaptation projects of nature-based solutions (NBS): river restoration (Germany), forest conservation (China), and landslide risk reduction (Italy). Building on a desktop study and open-ended interviews, our analysis adds evidence to the view that transformation is not an abrupt system change, but a dynamic complex process that evolves over time. While each of the NBS cases fails to fulfill all the transformation characteristics, there are important transformative elements in their visions, planning, and interventions. There is a deficit, however, in the transformation of institutional frameworks. The cases show institutional commonalities in multi-scale and cross-sectoral (polycentric) collaboration as well as innovative processes for inclusive stakeholder engagement; yet, these arrangements are ad hoc, short-term, dependent on local champions, and lacking the permanency needed for upscaling. For the public sector, this result highlights the potential for establishing cross-competing priorities among agencies, cross-sectoral formal mechanisms, new dedicated institutions, and programmatic and regulatory mainstreaming.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10113-023-02066-7.

Back to the surface – Daylighting urban streams in a Global North–South comparison

Many urban streams have vanished from the surface as a collateral effect of urban growth. Often, these buried streams have been forgotten, and only street names remind us of their existence. Reasons for stream burial include the gain of space for road or house construction or the use of stream water to transport wastewater. Today, restoration efforts to bring back fully canalized streams to the surface and to restore their stream bed (so-called daylighting) are being increasingly integrated into urban blue-green space planning, recognizing the high ecological and social value of urban streams, especially to support resilience against climate change impacts in cities. In this paper, we briefly revise the impacts of stream burial, present a series of case studies of daylighting from Europe (France, Switzerland, and Germany), and compare them with case studies from Asia (China, India, Taiwan). We found that high real estate prices, limited buffer riparian zone and resistance by the inhabitants were the greatest obstacles to stream daylighting projects. In contrast, economic gains from separating wastewater from rainwater and revival of cultural linkages with water were the strongest drivers to restore these streams. We then present methods on how to identify buried streams as candidates for daylighting and deliver criteria to select the most promising candidates. Acknowledging that each restoration project requires to be adapted to the local biophysical and local setting, we deliver a preliminary decision support system and a guideline for identifying the best candidate streams for daylighting projects, including the arguments in favor of restoration, the caveats, the social processes of decision-making, and perspectives for the integration of stream daylighting into urban climate change mitigation and adaptation concepts, in a Global North-South comparison.

Agroforestry Contributions to Urban River Rehabilitation

The context of urban rivers is one of pollution of their courses, the degradation of riparian habitats, the loss of biodiversity, and the marginalization of the human populations that live next to them. Due to urban growth, the hydrological dynamics in entire basins and the hydromorphology of rivers are changing. This situation increases flooding, decreases the availability of water for human use, and disconnects the rivers from the dynamics of the city. Agroforestry is the integration of cultural, wild, and domesticated diversity with use, conservation, and restoration objectives. These practices in cities can contribute to addressing the problems mentioned. We analyze agroforestry practices and the socio-ecological contributions to urban river rehabilitation. We review 37 experiences worldwide. Agroforestry practices included in the review are trees and hedgerows; wetland agroforestry; aquatic, botanical, edible, educational, and rain gardens; bioswales; green parking lots; food forestry; vegetation in alleys and streets; vertical terrace walls, among others. Agroforestry contributes to efforts to solve urban river problems, improve water quality and access, restore riparian habitats, enhance river hydromorphology, support local economies, and create a river culture. We emphasize promoting multi-relational people–river interactions based on theoretical and practical frameworks that integrate diverse disciplines, perspectives, and experiences.

Pilot-scale constructed bypass channel for urban river restoration: the remedial efficiency and the variance in biodiversity

Like the blood vessels of the cities, urban rivers play a significant role on maintaining the cities' sustainable development. In addition to the prevention of pollutants discharge and improving the river water quality, the restoration of the urban rivers' ecosystem should be well concerned. To fill this gap, a pilot-scale study with constructed bypass channel (CBC) was conducted. The pollutants reduction by the aquatic plants of the CBC was evaluated, and the similarities/differences of the aquatic biodiversity between the CBC and the natural rivers were analyzed. The results indicated that the mean removal efficiency of TP, NH₃-N, TN, and COD by the CBC was 66%, 60%, 52%, and 36%, respectively. Chlorophyta, Bacillariophyta, and Cyanophyta were the dominant phytoplankton phyla in the CBC which was in accordance with the studies conducted in the Dongjiang River and the Pearl River. During the study period of about 6 months, the population density and the biomass of the phytoplankton and the zooplankton increased over time. The quality of the influent dominated the aquatic organisms' diversity of the CBC. N-element dominated not only the phytoplankton variability, but also the bacterial species of the CBC. The timber pile and the submerged plant root soil were more suitable for the growth of the functional bacteria; thus, the construction of the river restoration infrastructures should avoid using large-scale cement materials. Overall, the study would improve the understanding of urban river restoration practice and provide guidance for future restoration practice especially from the aquatic ecological perspectives.

Governance models for nature-based solutions: Seventeen cases from Germany

Nature-based solutions (NBS) for mitigating climate change are gaining popularity. The number of NBS is increasing, but research gaps still exist at the governance level. The objectives of this paper are (i) to give an overview of the implemented NBS for flood risk management and mitigation in Germany, (ii) to identify governance models that are applied, and (iii) to explore the differences between these models. The results of a hierarchical clustering procedure and a qualitative analysis show that while no one-size-fits-all governance model exists, polycentricism is an important commonality between the projects. The study concludes by highlighting the need for further research on traditional governance model reconversion and paradigm changes. We expect the findings to identify what has worked in the past, as well as what is important for the implementation of NBS for flood risk management in future projects.

The third dimension in river restoration: how anthropogenic disturbance changes boundary conditions for ecological mitigation

The goals of the European Water Framework Directive changed the perspective on rivers from human to ecosystem-based river management. After decades of channelizing and damming rivers, restoration projects are applied with more or less successful outcomes. The anthropogenic influence put on rivers can change their physical parameters and result in a different morphological type of river. Using the Ammer River as an example, a comparison between applied systems of corridor determination based on historical maps and data; calculation of regime width; and the change in parameters and river typology are pointed out. The results showed (a) a change in stream power and morphology (b) great difference between the historical and the predicted river type and (c) that regulated rivers can have a near-natural morphology.

Cost-effective reduction of micro pollutants in the water cycle - Case study on iodinated contrast media

Surface waters, especially in densely populated areas, are facing multiple anthropogenic pressures. Micro pollutants are of growing concern. Improved analytical methods are used to focus on substances like ICM with a (high) potential of hazardous effects against water organisms or the water quality in general ICM are essential for instance in computer tomographic examinations in medical facilities. Discharge of ICM to the sewer system occurs via human urine excretions. Common waste water treatment plants do not eliminate these substances completely. Therefore, increasing concentrations are found in the rivers worldwide. The project MERK'MAL explored a potentially cost-effective measure to reduce ICM in the River Ruhr, located in Germany, North Rhine-Westphalia. The results from this pilot study show that urine bags are an effective measure to reduce ICM concentrations. During the urine collection with bags measurements of ICM concentrations have shown a reduction, compared to the baseline concentration that was measured at the same sampling point in the effluent of the corresponding waste water treatment plant. The ICM reduction ranged between 20 and 34% for the mean values and between 7 and 33% for the median value. Additional payment equivalent costs per examination with ICM are approx. 3.36 €, full costs including imputed costs are expected in a cost range of 5.38 € to 6.09 € per examination. The extension of the study is envisioned, helping to sustainably enhance water quality in the River Ruhr in terms of ICM concentrations.

Urban Stream and Wetland Restoration in the Global South—A DPSIR Analysis

In many countries of the Global South, aquatic ecosystems such as streams, rivers, lakes, and wetlands are severely impacted by several simultaneous environmental stressors, associated with accelerated urban development, and extreme climate. However, this problem receives little attention. Applying a DPSIR approach (Drivers, Pressures, State, Impacts, Responses), we analyzed the environmental impacts and their effects on urban hydrosystems (including stagnant waters), and suggest possible solutions from a series of case studies worldwide. We find that rivers in the Global South, with their distinctive geographical and socio-political setting, display significant differences from the Urban Stream Syndrome described so far in temperate zones. We introduce the term of ‘Southern Urban Hydrosystem Syndrome’ for the biophysical problems as well as the social interactions, including the perception of water bodies by the urbanites, the interactions of actors (e.g., top-down, bottom-up), and the motivations that drive urban hydrosystem restoration projects of the Global South. Supported by a synthesis of case studies (with a focus on Brazilian restoration projects), this paper summarizes the state of the art, highlights the currently existing lacunae for research, and delivers examples of practical solutions that may inform UNESCO’s North–South–South dialogue to solve these urgent problems. Two elements appear to be specifically important for the success of restoration projects in the Global South, namely the broad acceptance and commitment of local populations beyond merely ‘ecological’ justifications, e.g., healthy living environments and ecosystems with cultural linkages (‘River Culture’). To make it possible implementable/practical solutions must be extended to (often poor) people having settled along river banks and wetlands.