Introduction: Freshwater ecosystem restoration is vital for halting biodiversity loss, enhancing resilience, and securing ecosystem services amid climate and land use change. With major initiatives like the United Nations Decade on Ecosystem Restoration and the European Union's Nature Restoration Regulation gaining momentum, identifying multifunctional restoration strategies is increasingly important.

Objectives: This study examines which restoration measures in rivers, peatlands, and other wetlands deliver consistent benefits for both biodiversity and ecosystem services—key goals under EU restoration policies.

Methods: A structured Delphi survey was conducted with European experts in ecological restoration and ecosystem services. Restoration measures were compiled from scientific and gray literature, categorized into standardized types, and screened for data gaps. Measures with limited evidence were prioritized for expert evaluation. Experts assessed the expected effects of each measure on biodiversity and 18 ecosystem services through two survey rounds.

Results: Most restoration measures—especially hydrological and morphological interventions in rivers and vegetation-based actions in peatlands—were expected to strongly benefit biodiversity. Many also enhanced multiple ecosystem services, with river interventions such as restoring natural flow, channel structure, and habitat complexity showing the highest multifunctionality. Effects on provisioning services, particularly agricultural output, were mixed: some large-scale measures negatively affected productivity in intensively farmed areas. Peatland and wetland interventions showed more variable outcomes and greater uncertainty, linked to limited data and fewer expert responses.

Conclusions: The study identifies restoration measures that optimize ecological and societal outcomes and highlights key knowledge gaps, especially in peatland and wetland systems. Expert consensus supports evidence-based planning and strategies that align biodiversity goals with sustainable land use and ecosystem services.

Freshwater habitats and biota are among the most threatened worldwide. In Europe, significant efforts are being taken to counteract detrimental human impacts on nature. In line with these efforts, the MERLIN project funded by the H2020 program focuses on mainstreaming ecosystem restoration for freshwater-related environments at the landscape scale. Additionally, the Dammed Fish project focuses on one of the main threats affecting European Networks—artificial fragmentation of the river. Meeting the objectives of both projects to work on a large, pan-European scale, we developed a novel spatial database for river units.

These spatial units, named River Restoration Units (R2Us), abide by river network functioning while creating the possibility of aggregating multiple data sources with varying resolutions to size-wise comparable units. To create the R2U, we set a methodological framework that departs from the Catchment Characterization and Modelling—River and Catchment Database v2.1 (CCM2)—together with the capabilities of the River Network Toolkit (v2) software (RivTool) to implement a seven-step methodological procedure. This enabled the creation of 11,557 R2U units in European sea outlet river basins along with their attributes. Procedure outputs were associated with spatial layers and then reorganized to create a relational database with normalized data. Under the MERLIN project, R2Us have been used as the spatial analysis unit for a large-scale analysis using multiple input datasets (e.g., ecosystem services, climate, and European Directive reporting data). This database will be valuable for river management and conservation planning, being particularly well suited for large-scale restoration planning in accordance with European Nature legislation.

Metacommunity theory offers a compelling framework for understanding the processes that govern biodiversity patterns across space and time. Yet, a persistent challenge remains: integrating the wide array of ecological drivers into a unified model using observational data from complex, dynamic ecosystems. In this study, we present a novel, process-explicit path modeling approach that bridges recent theoretical advances in metacommunity ecology with empirical data. Focusing on fish communities in the floodplains of the Danube River, we leverage environmental DNA (eDNA) metabarcoding to characterize community composition across a spatiotemporal network of sites. We partition beta diversity into its species replacement and richness difference components and apply structural equation modeling to evaluate the relative influence of multiple ecological drivers—including spatial and temporal dispersal, demographic stochasticity, abiotic filtering, and interspecific interactions. Our results reveal that river-floodplain fish metacommunities are shaped by a complex web of interacting processes.

Notably, we find that species replacement is primarily driven by spatial distance and environmental filtering, while richness differences are more influenced by biotic interactions and community size. Lateral hydrological connectivity emerged as a pivotal landscape feature, governing beta diversity both directly and indirectly through its modulation of local environmental conditions. This connectivity acted as a structural conduit, mediating dispersal, environmental heterogeneity, and biotic interactions. By disentangling the contributions of multiple processes, our model underscores the dominant role of spatial structuring and abiotic filtering over temporal dynamics and biotic interactions in shaping metacommunity assembly. The model also demonstrates improved explanatory power and stronger model fit, outperforming previous studies. These findings underscore the need for integrative frameworks that consider the simultaneous influence of multiple ecological processes, particularly in highly dynamic systems like river-floodplains. Our conceptual and modeling approach advances metacommunity theory by offering a robust, data-driven means to assess complex assembly mechanisms and by emphasizing the critical role of connectivity and habitat complementarity in sustaining biodiversity within dynamic landscapes.

To make river basins more climate resilient, provide a better living environment for people and other organisms, the EU encourages integrated river and floodplain management (RFM) and calls for restoration of 25,000 km of EU rivers to a free-flowing state in the EU Nature Restoration Law. To support decision making in this domain, there is a need for a holistic assessment framework. However, most policy appraisal studies in river management to date have a limited scope and focus on impacts of measures in a single domain, such as flood risk reduction or water quality. In this study we address this gap by using quantitative models to analyse the supply of 13 ecosystem services under various RFM strategies for the Rhine Branches in the Netherlands. We use a mix of biophysical and monetary indicators to quantitatively assess ecosystem services and the trade-offs involved in different RFM strategies.

The results show that strongly regulated, mono-functional RFM has overall lower ES supply than more integrated, multifunctional RFM strategies with rehabilitated floodplains. The latter generally increase ES supply across all domains (provisioning, regulating, cultural), with the exception of crop and fodder production in the floodplains. Overall, our results can inform formulation and communication on RFM strategies in the Netherlands and elsewhere. Also, our approach serves as a demonstration of how the ES framework can be used to support quantitative impact assessment in this domain.

Disruptions of the longitudinal river continuum by artificial barriers have been widely recognized to impact aquatic biodiversity. However, while consequential connectivity changes have been researched extensively, the temporal component has been largely disregarded. Therefore, we investigate how almost 500 large artificial barriers, and later fish migration aids (FMAs), have affected longitudinal connectivity, specifically the connections between suitable habitats, along an Austrian river network since the beginning of the 20th century. For this purpose, a graph theoretic approach is deployed that integrates structural and functional aspects, illustrating connectivity changes from the perspective of a characteristic migratory fish species Chondrostoma nasus (Linnaeus 1758).

Furthermore, different barrier passability scenarios, partly based on empirical findings, are assessed to account for uncertainties and identify to what extent passability must be restored to reach a proposed restoration goal. Our results illustrate that the most significant loss of connectivity has occurred after the beginning of the 20th century. Particularly, barriers constructed in the main stem of the river network, the Danube, have been identified as drivers of connectivity loss and, hence, as bottlenecks for connectivity restoration. While FMAs have partially restored connectivity, the remaining loss has been estimated between 31.7% and 60.7% across barrier passability scenarios. Contrastingly, despite the construction of roughly 350 artificial barriers, connectivity loss at the beginning of the 20th century ranged only between 6.8% and 8.3%.

Therefore, since a full restoration must be deemed aspirational, we suggest restoring connectivity to an extent similar to the beginning of the 20th century. To reach this restoration goal, our results suggest that even the passability of barriers equipped with FMAs must be increased, and if this cannot be achieved, barrier decommissioning needs to be considered. Finally, we identify a need for a transparent assessment of quantitative barrier passability and conclude that the construction of further barriers must be considered unsustainable as long as previous connectivity and habitat losses are not compensated.

Rewetting drained peatlands and restoring their hydrological conditions can contribute to climate mitigation by reducing soil greenhouse gas emissions. However, re-establishment of degraded peatlands can pose a risk of phosphorus (P) mobilization due to anaerobic conditions that develop with rewetting. Harvesting plant biomass which removes nutrients accumulated in vegetation, has been proposed as a mitigation measure to address this risk. However, the time required to deplete P soil pools remains poorly understood.

To address this knowledge gap, we investigated the impact of biomass harvesting in Kvorning, Denmark, scheduled for rewetting in 2025. We aimed to quantify P removal through biomass harvesting and assess how it changed over time since harvesting began in 2018. We examined whether changes in the plant community reflected P limitation following biomass harvesting and promoted improvements in vegetation diversity and habitat quality.
Results showed that biomass harvesting removed considerable amounts of nutrients. However, removal rates did not decline over time, indicating no evidence of soil P depletion over the six-year study period. Moreover, nutrient removal rates were higher in Wet areas (78.6 kg N and 7.9 kg P/ha/year) than in Drier ones (62.0 kg N and 6.1 kg P/ha/year).

Although species composition and community-level traits shifted following harvesting, there was no change in overall plant community structure. Our findings suggest that biomass harvesting can be an effective long-term strategy to mitigate nutrient release, though unlikely to deplete soil P rapidly without complementary interventions.

Stepping up ecosystem restoration is critical to achieving pressing policy targets, but as well as significant benefits, there are also multiple challenges particularly associated with restoring at landscape scale. These relate to the complexity of ecosystems, land uses, and social factors within a landscape and the scale at which sustainable funding and effective monitoring are required. Here we present a summary of discussions from a symposium at the Society for Ecological Restoration—Europe conference, addressing five key topics related to scaling up restoration in Europe: implementation, stakeholder engagement, local economies, financing, and monitoring.

Common barriers include inflexible political systems and traditional conservation project thinking, as well as the complexities and time required to work effectively and sustainably across disciplines, sectors, and geographical boundaries. However, opportunities are identified in relation to innovative financing systems and monitoring technologies, the development of nature-based economies, and the strength and sustainability that comes from effectively and deeply engaging a wide diversity of stakeholders. Capitalizing on these prospects could enable landscape-scale ecosystem restoration to play a significant role in meeting global targets for nature, climate, and people.

Freshwater ecosystems across Europe face significant degradation, with agricultural practices playing a central role. The 2023–2027 Common Agricultural Policy (CAP) introduces new eco-schemes that could support river restoration, a key goal of EU environmental legislation. This study presents a systematic analysis of eco-schemes in all 27 EU CAP Strategic Plans, assessing their alignment with river restoration goals. We reviewed over 130 approved eco-schemes, classifying them according to their potential to support eleven predefined restoration actions (e.g., floodplain reconnection, instream habitat improvement). Support was categorized as direct, indirect, potential, or not supported. The analysis combined AI-assisted text processing with manual validation. Results reveal considerable variation in how Member States use eco-schemes to support river restoration. While some countries offer multiple schemes with direct or indirect relevance, most focus on maintaining existing practices. Only a limited number explicitly support actions like riparian buffer restoration or wetland creation.

Over 30% of all eco-schemes fall into the “potential” category, where design could be enhanced to support freshwater restoration more explicitly. Although river restoration is not a core target of CAP eco-schemes, this new instrument creates strategic opportunities to address freshwater degradation. The current implementation, however, reflects limited ambition and uneven alignment with EU water policy goals. The paper proposes adjustments to scheme design and classification methods to better embed blue infrastructure restoration within the CAP framework. This study offers the first EU-wide analysis of eco-schemes for river restoration, providing a critical baseline for future policy development and mid-term CAP revisions.

The study explores the application of a Theory of Change (ToC) framework in 18 large-scale freshwater restoration projects within the context of the European Green Deal and the recently adopted Nature Restoration Regulation. By leveraging a participatory approach, the research examines the effects of freshwater restoration measures across three ecosystem clusters: peatlands and wetlands, small streams, and large rivers. In a conceptual model, restoration measures were connected with transdisciplinary goals, assessing biophysical, social and economic outcomes. The findings highlight the effectiveness of Nature-based Solutions in advancing climate resilience, biodiversity gains, and social equity while identifying potential trade-offs and negative effects.

The ToC framework proved valuable in guiding restoration planning, facilitating stakeholder engagement, and enabling adaptive management in accordance with the Nature Restoration Regulation’s requirements. However, the study underscores the need for clearly defined quantitative targets to enhance systematic monitoring and evaluation, ensuring full and sustainable alignment with broader European objectives.

Introduction: In the Upper Danube River, a key goal of river–floodplain restoration is to enhance hydrological connectivity and reduce aquatic habitat isolation and terrestrialization. To evaluate restoration effectiveness, it is crucial to understand the functional responses of freshwater biodiversity and the role of connectivity and environmental factors.

Objectives: In this study, we compared oligochaetes and chironomids across control and impacted sites before, short-term, and long-term after restoration in a river–floodplain stretch of the Donau-Auen National Park.

Methods: We applied a Before-After-Control-Impact (BACI) design to analyze the effects of restoration-induced connectivity changes on the taxonomic and functional composition and diversity of these groups. A graph theoretical approach and partial least squares regressions were used to assess the impact of connectivity changes on taxonomic and functional diversity.

Results: Our BACI analysis showed positive effects of restoration on oligochaete diversity, but long-term terrestrialization processes outweighed restoration impacts. Traits such as stream zonation preference, current preference, body size, dispersal strategy, drift propensity, and adult lifespan exhibited short-term restoration effects for both groups, returning to pre-restoration conditions in the long term. For oligochaete functional diversity, connectivity was influential shortly after restoration, while environmental factors became more significant over time.

Conclusion: Our results highlight both the potential for short-term improvements and the challenges of maintaining restoration-driven benefits over time.

This study investigates the integration of river restoration with the Common Agricultural Policy (CAP), focusing on the differences between European Union (EU) and Portuguese documents regarding river restoration terms. A thematic content analysis highlights that despite the varying document sizes, the proportion of mentions related to river restoration and management is similar, indicating comparable importance. Portuguese legislation prioritizes water management due to geographic and climatic conditions, emphasizing conditionality over proactive measures. The significance of wetlands and peatlands in Portuguese documents is linked to Good Agricultural and Environmental Conditions (GAEC 2) regulations, but active restoration terms are underutilized as opposed to passive restoration, reflecting a maintenance-oriented approach.

EU CAP documents emphasize agricultural impacts on the environment, aligning with the Water Framework Directive and addressing key topics such as wetlands, buffer zones, and agricultural constraints near waterbodies. The Portuguese CAP Strategic Plan restricts agri-environmental commitments financing to Natura 2000 areas, excluding much farmland from support, with eco-schemes and agri-environmental measures being limited and underfunded. This study underscores the need for policy development to increase the adoption of voluntary, incentive-based measures for more effective river restoration within European cropland.

Grassland on dikes and in floodplains offers great potential to enhance biodiversity, particularly in urban areas. This study investigates the effects of changing the management from intensive mowing to reduced management on community composition, species richness, Shannon diversity, and functional traits for vegetation, general arthropods, and epigean carabids. Along the rivers Emscher and Lippe, 16 sites were studied. Reduced management’ was characterized by sowing native species and mowing twice annually with cutting removal, while intensive management’ included frequent mowing and mulching. Sites were investigated where reduced management was established recently or several years ago. Reduced management increased species richness and altered community composition across all groups compared to intensive management.

Plant species richness increased by 5.7, general arthropods by 4.8, and epigean carabids by 0.7. No significant differences were observed between short- and long-term implementation. Ruderal and stress-tolerant plant species dominated vegetation in intensively managed sites, while reduced sites supported more specialized feeding types across insect species and floodplain-specific carabids. Larger, univoltine arthropods were more common in reduced sites. Sowing native grassland species and changing the management from intensive to reduced mowing can increase biodiversity and favor specialist species. This effect is achieved within a short time after implementation and remains effective in the long term. Conversion from intensive to reduced management is, therefore, an important strategy for increasing biodiversity and resilience of grasslands in urban floodplains.

Digital reports are published, recording the key results of the MERLIN Systemic analysis of restoration impacts across the 13 European Green Deal Policy areas for 18 MERLIN Restoration Case Studies.
Reports are published on the MERLIN Knowledge Hub, allowing users to navigate through each criterion following a progressive disclosure approach which directs towards more detailed evidence in respective deliverables.

A description of the systemic and integrated analysis approach developed through the MERLIN Monitoring and Assessment Framework, including estimates of confidence and direction of impact for each of the EGD assessment indicators.
The digital reports are designed to provide real-life examples from the MERLIN community, to inspire the wider restoration community and to demonstrate the potential to recognise multiple benefits of restoration as well as positive and negative trade-offs.

River-floodplain connectivity is a critical ecological process influencing biodiversity and ecosystem functions. However, the impact of changes in this connectivity, particularly its loss, on biodiversity in floodplains remains insufficiently studied. This study aimed to assess how connectivity influences biodiversity metrics and whether it directly affects biodiversity indices for selected species groups, beyond its indirect influence through environmental variables. We used structural equation modelling to separate the direct effects of connectivity on plant and carabid beetle diversity from indirect effects mediated by flooding regimes, soil properties, and pollution in the Elbe River floodplains. We compared results from connected and decoupled floodplain sections to understand how these relationships change when connectivity is lost.

Connectivity showed significant direct effects on most biodiversity metrics for both plants and carabids. For carabids, higher connectivity was associated with lower species richness and higher proportions of indicator species for wet grasslands, independent of intermediate factors such as flooding or soil conditions. For plants, higher connectivity was associated with higher species and functional richness, though only through indirect effects. Overall, connectivity had a positive impact on biodiversity, fostering higher species and functional diversity without leading to highly specialised, species-poor communities. Additionally, the models were largely consistent between connected and decoupled floodplains, suggesting that decoupling does not fundamentally alter the ecological mechanisms governing biodiversity, and that recovery through restoration is possible. Our findings highlight the complex role of river-floodplain connectivity in shaping floodplain biodiversity. Maintaining and restoring this connectivity is essential for promoting diverse and resilient floodplain ecosystems.

Sustainable management of lakes requires us to overcome ecological, economic, and social challenges. These challenges can be addressed by focusing on achieving ecological improvement within a multifaceted, co-beneficial context. In-lake restoration measures may promote more rapid ecosystem responses than is feasible with catchment measures alone, even if multiple interventions are needed. In particular, we identify restoration methods that support the overarching societal target of a circular economy through the use of nutrients, sediments, or biomass that are removed from a lake, in agriculture, as food, or for biogas production. In this emerging field of sustainable restoration techniques, we show examples, discuss benefits and pitfalls, and flag areas for further research and development.

Each lake should be assessed individually to ensure that restoration approaches will effectively address lake-specific problems, do not harm the target lake or downstream ecosystems, are cost-effective, promote delivery of valuable ecosystem services, minimize conflicts in public interests, and eliminate the necessity for repeated interventions. Achieving optimal, sustainable results from lake restoration relies on multidisciplinary research and close interactions between environmental, social, political, and economic sectors.

Beyond preferences for particular species of tree, bark-foraging birds are associated with various tree characteristics such as decay stage, trunk diameter, or bark roughness. Our objectives were to study the winter foraging ecology of different bark-foraging bird species in the highly diverse floodplain forests of Donau-Auen National Park (Austria) by examining the importance of tree species and characteristics. We used 'first-foraging' observations on the great spotted woodpecker (Dendrocopos major), middle spotted woodpecker (Leiopicus medius), Eurasian nuthatch (Sitta europaea), treecreepers (Certhia spp.), great tit (Parus major), Eurasian blue tit (Cyanistes caeruleus), and marsh tit (Poecile palustris).

We examined bird-tree relationships with a bird-plant network approach, where we compared traits of trees and their preferences among avian species. The five most important tree species relative to distance-weighted fragmentation were European white elm (Ulmus laevis), pedunculate oak (Quercus robur), common ash (Fraxinus excelsior), and white and black poplar (Populus alba, P. nigra). Avian taxa differed only in the use of tree condition, where woodpeckers used decayed and dead trees more than tits. Most species preferred trees of larger trunk diameter with rougher bark. We suspect that changes in these highly diverse floodplain forest stands will eventually lead to changes in bark-foraging bird assemblages.

For the protection of such highly diverse floodplain forests, conservation-based water management practices will be crucial to maintaining a sufficient groundwater table. Our findings also suggest that forest management practices should focus on more diverse commercial forest stands with a critical amount of secondary tree species, a variety of size classes, varying tree conditions, and species with different bark roughness classes.

Increasing human activity is altering the structure of forests, which affects the composition of communities, including birds. However, little is known about the key forest structure variables that determine the richness of bird communities in European temperate oak forests. We, therefore, aimed to identify key variables in these habitats that could contribute to the design of management strategies for forest conservation by surveying 11 oak-dominated forest sites throughout the mid-mountain range of Hungary at 86 survey points to reveal the role of different compositional and structural variables for forest stands that influence the breeding bird assemblages in the forests at the functional group and individual species levels.

Based on decision tree modelling, our results showed that the density of trees larger than 30 cm DBH was an overall important variable, indicating that large-diameter trees were essential to provide diverse bird communities. The total abundance of birds, the foliage-gleaners, primary and secondary cavity nesters, residents, and five specific bird species were related to the density of high trunk diameter trees. The abundance of shrub nesters was negatively influenced by a high density of trees over 10 cm DBH. The density of the shrub layer positively affected total bird abundance and the abundance of foliage gleaners, secondary cavity nesters and residents.

Analysis of the co-dominant tree species showed that the presence of linden, beech, and hornbeam was important in influencing the abundance of various bird species, e.g., Eurasian Treecreeper (Certhia familiaris), Marsh Tit (Poecile palustris) and Wood Warbler (Phylloscopus sibilatrix). Our results indicated that large trees, high tree diversity, and dense shrub layer were essential for forest bird communities and are critical targets for protection to maintain diverse and abundant bird communities in oak-dominated forest habitats.

1. Trait-based approaches have received increasing interest among freshwater scientists given their capacity to predict community structure and biodiversity effects on ecosystem functioning. However, the inconsistent development and use of trait concepts and terms across freshwater scientific disciplines may have limited realisation of the potential of traits.
   
   
2. Here, we reviewed trait definitions and terms use to provide recommendations for their consistent application in freshwater science. To do so, we first reviewed literature to identify established trait definitions, historical and current use of trait terms and challenges restricting the application of trait-based approaches in freshwater science. Next, we surveyed 414 freshwater researchers from 54 countries to assess variability in the current use of trait terminology in relation to respondent characteristics (i.e., professional experience, geographical region, research discipline, and focal freshwater ecosystem, biotic group, and ecosystem function).
   
   
3. Our literature review identified two well-established trait definitions, which emphasise individual phenotypic characteristics that influence either eco-evolutionary aspects (i.e., organism performance and fitness) or ecosystem dynamics and processes (i.e., responses to the environment and/or effects on ecosystem functioning). Publications used a range of trait-related terms and their frequency of use varied among scientific fields. The term functional trait dominated fields such as biodiversity conservation, environmental sciences and ecology, plant sciences and microbiology. In contrast, the terms biological trait, functional trait, and species trait were used with similar frequencies in fields such as entomology, fisheries, marine and freshwater biology, and zoology. We also found that well-established trait definitions are difficult to apply to freshwater unicellular organisms, colonial multicellular organisms, genomic information, and cultural traits.
   
   
4. Our survey revealed highly inconsistent use of trait terms among freshwater researchers. Terms including biological trait, functional trait, structural measure, and ecosystem function were commonly used to describe the same traits or functions. Variability in the use of terms was generally explained by research discipline, geographical region, and focal biotic group and ecosystem functions.
   
   
5. We propose making the trait concept flexible enough to be applicable to all freshwater biota and their characteristics, while keeping and integrating links to eco-evolutionary and ecosystem aspects. Specifically, our new definition expands the established functional trait definition by considering also supra-individual scales of trait measurement (colonial- or community-mean traits), genotypic traits (e.g., functional gene markers of enzymes) and cultural traits (e.g., feeding behaviours, communication skills). To reduce terminological ambiguity, we also recommend that researchers define trait terms, prioritising the use of functional trait as an overarching term over alternative terms (e.g., biological trait), and restricting specific terms (e.g., morphological trait) to situations in which such precision is desirable. The findings of our integrative study could help to improve terminological consistency across freshwater disciplines and to better recognise the potential of traits to elucidate the mechanisms behind ecological patterns.

Water-scarce regions, like the Mediterranean, face worsening conditions due to climate change, intensifying pressure on key economic sectors such as hydropower. Additionally, environmental conservation policies, particularly the implementation of environmental flows, present challenges for hydropower systems. Certainty regarding the impact of these factors on future hydropower production is crucial for informed decision-making in the transition to sustainable energy. This study introduces S + HydPower, a tool coupled with SWAT+ to assess climate change and watershed management effects on small hydropower plant (SHP) systems. In this study, we used this tool to investigate the consequences of implementing environmental flows and climate change on run-of-river SHPs in the Catalan River Basin District (CRBD), in Catalonia. The results show that applying environmental flows would lead to a significant 27% reduction in SHP production. However, this reduction would represent only 0.25% of the region’s current energy demand.

Furthermore, the study reveals a potential 38% to 73% reduction in SHP production by the end of the twenty-first century due to the combined effects of environmental flows and climate change. This suggests a substantial decline in run-of-river SHP’s contribution to the CRBD’s electricity supply. These findings emphasize the need to explore alternative and sustainable energy sources to ensure the long-term reliability and resilience of the region’s energy supply.

Catchment urbanisation results in urban streams being exposed to a multitude of stressors. Notably, stressors originating from diffuse sources have received less attention than stressors originating from point sources. Here, advances related to diffuse urban stressors and their consequences for stream benthic communities are summarised by reviewing 92 articles. Based on the search criteria, the number of articles dealing with diffuse urban stressors in streams has been increasing, and most of them focused on North America, Europe, and China. Land use was the most common measure used to characterize diffuse stressor sources in urban streams (70.7 % of the articles characterised land use), and chemical stressors (inorganic nutrients, xenobiotics, metals, and water properties, including pH and conductivity) were more frequently reported than physical or biological stressors. A total of 53.3 % of the articles addressed the impact of urban stressors on macroinvertebrates, while 35.9 % focused on bacteria, 9.8 % on fungi, and 8.7 % on algae.

Regarding ecosystem functions, almost half of the articles (43.5 %) addressed changes in community dynamics, 40.3 % addressed organic matter decomposition, and 33.9 % addressed nutrient cycling. When comparing urban and non-urban streams, the reviewed studies suggest that urbanisation negatively impacts the diversity of benthic organisms, leading to shifts in community composition. These changes imply functional degradation of streams. The results of the present review summarise the knowledge gained to date and identify its main gaps to help improve our understanding of urban streams.

The 17 MERLIN Regional Scalability Plans (RSPs) offer visions for upscaling restoration at wider landscape levels with a time horizon up to 2050 created through collaborative efforts to upscale freshwater restoration initiatives. The RSPs address 'why', 'where', 'what, 'how', and 'who' questions to upscale freshwater restoration.

As the integrity and extent of many natural ecosystems continues to decline, the concept of Nature-based Solutions (NbS) is gaining traction as a means to reverse such trends. However, uptake of an NbS approach across society is often piecemeal or partial. This paper argues that a deeper connection with the literature on transformations will help realise the full potential of NbS for enabling sustainable futures. Whilst others have already noted the concept of transformations to be relevant to NbS, many insights from the sustainability transformations literature remain underutilised by those working with NbS.

In this paper, we provide a conceptual framework to enable more ambitious and widespread uptake of NbS. We do this by identifying and drawing on key conceptual perspectives and frameworks from the sustainability transformations literature. This framework identifies key components (current system, future visions, process and an iterative approach) to consider when planning strategic actions. The framework strengthens the links between transformations and NbS concepts for a variety of stakeholders: as well as guiding NbS practitioners, it can also support action-orientated research to help steer NbS to achieve transformational change.

Information about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS-based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km² as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m²). This is sufficient, as currently, only an estimated maximum number of 750 adults exist.

Suitable spawning habitat is mainly located in the German state of North Rhine-Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.

Water-scarce regions, like the Mediterranean, face worsening conditions due to climate change, intensifying pressure on key economic sectors such as hydropower. Additionally, environmental conservation policies, particularly the implementation of environmental flows, present challenges for hydropower systems. Certainty regarding the impact of these factors on future hydropower production is crucial for informed decision-making in the transition to sustainable energy. This study introduces S + HydPower, a tool coupled with SWAT+ to assess climate change and watershed management effects on small hydropower plant (SHP) systems. In this study, we used this tool to investigate the consequences of implementing environmental flows and climate change on run-of-river SHPs in the Catalan River Basin District (CRBD), in Catalonia. The results show that applying environmental flows would lead to a significant 27% reduction in SHP production. However, this reduction would represent only 0.25% of the region’s current energy demand. Furthermore, the study reveals a potential 38% to 73% reduction in SHP production by the end of the twenty-first century due to the combined effects of environmental flows and climate change. This suggests a substantial decline in run-of-river SHP’s contribution to the CRBD’s electricity supply. These findings emphasize the need to explore alternative and sustainable energy sources to ensure the long-term reliability and resilience of the region’s energy supply.