Rivers are increasingly fragmented and degraded, yet the European Union Nature Restoration Regulation calls for restoring at least 25,000 kilometres of free-flowing rivers by 2030. Translating this ambition into effective implementation remains challenging because restoration priorities differ across ecological, social, economic, and governance contexts. Here, we synthesize expert knowledge from 45 countries through a structured, multi-step prioritization process to identify research priorities for restoring free-flowing rivers in Europe. We identified 27 priorities and analysed how expert background and spatial context influenced their ranking. Restoration priorities differed systematically depending on whether experts emphasized ecological integrity, community engagement, economic considerations, or governance capacity, revealing clear patterns in how disciplinary and professional perspectives shape implementation pathways. This demonstrates that restoration strategies cannot be universal but must be adapted to local and regional political, institutional, and ecological conditions. Building on these findings, we propose a structured prioritisation framework that links barrier removal, connectivity restoration, governance mechanisms, and policy instruments to context-specific needs. Together, our results provide an empirically grounded and implementation-oriented roadmap to support European Union Member States in delivering ambitious river restoration targets in a context-sensitive and socially robust manner.

ABSTRACT Floodplains are among the most diverse freshwater ecosystems, yet they are increasingly threatened by human‐induced alterations. Recent research has shown that the ecological impacts of alien species in these systems can rival those of other anthropogenic disturbances. Effective management and mitigation strategies depend on accurate assessments of the distribution and temporal dynamics of alien species. However, traditional fish sampling methods are often inadequate in floodplains because their high spatial and temporal heterogeneity makes it impossible to apply a single traditional method effectively across different habitat types. In this study, we investigated how local habitat characteristics and regional‐scale processes influence habitat use and the temporal dynamics of alien fish abundance inferred from environmental DNA in Danubian floodplain systems. By integrating community‐ and species‐level analyses, we found that lateral hydrological connectivity is a key driver shaping alien fish community assembly, although the influence of other environmental factors, such as the local habitat structure, water chemistry, and land use, varied across taxa. We also revealed that the temporal dynamics of alien species were generally independent of local‐ and regional‐scale drivers. This suggests that extrinsic factors like hydrology, connectivity, and resource availability may have only a limited influence on short‐term eDNA‐derived abundance fluctuations of alien fishes in floodplains. These findings have practical implications: management effectiveness is likely to vary across spatial scales and species, and control efforts may be more successful in areas where alien fish populations are less stable. Importantly, our study demonstrates that eDNA metabarcoding is a powerful tool for monitoring alien species in complex and dynamic environments such as floodplains. It enables efficient, non‐invasive, and fine‐scale detection of spatial and temporal patterns that would be challenging to capture through conventional sampling, thereby enhancing our ability to inform targeted and adaptive management strategies.

Dynamic heterogeneous metacommunities can be analyzed as complex networks. However, the interplay of species interactions, local environmental conditions, and spatiotemporal dispersal remains poorly understood. We assess the relative importance of these drivers in structuring river-floodplain metacommunities based on a spatiotemporal eDNA dataset. We applied Bayesian network learning to infer species interactions, spatiotemporal dynamics, and the importance of environmental factors, and used graph theory to summarize and analyze the patterns in the derived networks. Our analysis revealed distinct sub-communities linked by interacting species, spanning a gradient from environmentally filtered to dispersal-driven. Top predators and invasive species are identified as key connectors, being most important in regulating network dynamics and cohesion. Our findings highlight that combining Bayesian networks with graph theory has high potential to uncover the causal structure of metacommunities and provide a mechanistic understanding of community assembly in dynamic ecosystems, informing ecosystem management in dynamic landscapes.

In Europe, ecological restoration efforts remain restricted and fragmented, with limited success and coordination across policies. The newly adopted Nature Restoration Regulation aims to address these challenges by setting ambitious, legally binding restoration targets. For freshwater ecosystems, its success depends on better integration of existing legislative frameworks, particularly the Habitats Directive (HD) and the Water Framework Directive (WFD). We present a novel European-scale modeling framework that for the first time, combines HD and WFD-related indicators, and applies specific Bayesian Network features, to achieve: i) a Europe-wide status prediction to identify areas with potential for restoration, conservation or mitigation measures, including spatially explicit information on uncertainty and data gaps, and ii) spatially explicit restoration targets, such as lateral and longitudinal connectivity improvements, derived through backward inference. Model validation demonstrated acceptable performance for six of twelve HD groups, including Bogs, Mires, Fens, as well as Amphibia, Fish and Plants, while sensitivity analysis indicated that taxon-specific responses were primarily driven by pressures from hydrology, morphology, and organic pollution. We provide a large-scale data-driven tool to maximize the ecological impact of restoration efforts across Europe, support efficient resource use, and help policymakers to direct efforts where they are most likely to succeed.

This study quantified how vegetation type and seasonality influence soil–atmosphere exchanges of CO2, CH4, and N2O across Lubigi Wetland, an urban tropical wetland in Uganda receiving wastewater effluent and stormwater from Kampala. Four sites were examined: an upstream Vossia cuspidata zone near inflows, an upstream non-vegetated mudflat, a midstream Phragmites mauritianus stand, and a downstream Cyperus papyrus section. Monthly static chamber measurements were conducted over 12 months, spanning wet and dry seasons, to assess spatial and temporal flux patterns, calculate site-specific global warming potentials (GWPs), and relate emissions to hydrology and soil characteristics.CO2 and N2O fluxes peaked during the dry season, especially in the upstream Vossia zone. CH4 emissions were also highest in the dry season, with Phragmites areas producing the strongest fluxes and mudflats the lowest. Hydrology was the main controlling factor: water levels below 50 cm promoted CO2 and N2O hotspots, while levels above 50 cm favored CH4 emissions. Across the wetland, CH4 contributed the largest share of annual GWP (about 55.6%), followed by CO2 (39.8%). The highest GWP occurred in the Phragmites zone due to sustained CH4 emissions, while mudflats had the lowest.Carbon and nitrogen cycles were tightly linked, with negative CO2–CH4 and positive CO2–N2O relationships. CH4 emissions were positively associated with microbial biomass carbon and negatively with bulk density. Vegetated soils contained higher organic carbon and nitrogen than mudflats. Management should prioritize CH4 mitigation, improve wastewater treatment, and apply seasonally adaptive water-level management to reduce overall GWP while maintaining ecosystem functions.

Abstract. Tropical wetlands significantly impact greenhouse gas (GHG) budgets and carbon storage: however data from sub-Saharan African (SSA) remain limited. Highland valley-bottom wetland (HVBW) agriculture supports millions, yet its effects on GHG emissions and carbon storage remain undocumented. This study quantified soil emissions of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) in the Taita Hills, Kenya, from 12 converted, 10 recovering, and one reference (intact) HVBWs. Agricultural conversion shifted wetland emissions from CH₄ to N₂O dominance. Converted HVBWs were N₂O sources (2.7 kg N₂O–N ha⁻¹yr⁻¹), driven by elevated soil nitrate, whereas the intact wetland was an N₂O sink (−0.3 kg N₂O–N ha⁻¹ yr⁻¹), with high soil moisture and high soil C/NO₃⁻–N ratio suggesting complete denitrification. Recovering HVBWs showed intermediate N₂O emissions (0.6 kg N₂O–N ha⁻¹ yr⁻¹). CO₂ emissions were similar between converted and recovering HVBWs (10,850 vs. 11,031 kg CO₂–C ha⁻¹ yr⁻¹) but lower in the intact (2,923 kg CO₂–C ha⁻¹ yr⁻¹). CH₄ emissions were highest in the intact HVBW (2,757 kg CH₄–C ha⁻¹ yr⁻¹), intermediate in recovering sites (879 kg CH₄–C ha⁻¹ yr⁻¹), and lowest in converted sites (37 kg CH₄–C ha⁻¹ yr⁻¹). The intact HVBW had 224 Mg C ha⁻¹, indicating carbon loss rates of 2.6 Mg C ha⁻¹ yr⁻¹ over 45 years for converted HVBWs. Restoring Taita Hills wetlands would sequester 1.1 Mg C ha⁻¹ yr⁻¹, offsetting ~0.0005 % of Kenya's annual agricultural GHG emissions, or 9.8 % when scaled nationally. These findings highlight trade-offs between GHG emissions and carbon storage in HVBWs, with wetland recovery promoting functional restoration and long-term carbon sequestration in SSA.

Monitoring microbial water quality is essential for understanding pollution dynamics and associated public health risks, particularly in rapidly urbanizing regions of developing countries. This study assessed seasonal variations in physicochemical conditions and microbiological indicators along the Lubigi wetland, a tropical riverine system receiving stormwater and wastewater from Kampala's urban infrastructure. Over a 17-month period, water samples were collected from six sites during dry and wet seasons and analyzed for Escherichia coli, faecal coliforms, heterotrophic plate counts (HPC), Enterococcus, and Salmonella species. Results showed that nitrogen compounds and pathogenic indicators were associated with stormwater runoff, whereas phosphorus, organic matter, and HPC were linked to wastewater effluent. During the dry season, E. coli concentrations declined significantly along the wetland, while Enterococcus decreased by 58.6% during the wet season. In contrast, faecal coliforms and HPC showed limited attenuation below 20% and persisted at high concentrations across both seasons. Overall, pollutant loads from the Nsooba channel and the Lubigi sewage treatment plant exceeded the wetland's natural treatment capacity, resulting in sustained microbiological contamination and increased risks to downstream water quality and public health. These findings underscore the need for improved urban water infrastructure and source-based pollution control rather than reliance on natural attenuation alone.

This study aims to characterize shoreline fish assemblages along different bank habitat types in the fragmented Austrian Danube and to investigate the impacts of fragmentation and habitat alterations caused by the construction of hydropower plants (HPPs). Nocturnal electrofishing surveys were conducted over 2 years in three river reaches separated by HPPs forming distinct sub-ecosystems within a larger Danube meta-ecosystem. The upper two reaches include both flowing and impounded sections, while the lowermost reach is free flowing. Of 46 species caught, 15 typical Danube species were selected for detailed analysis. Fish assemblages and abundance were compared across five river sections with varying longitudinal connectivity, four bank habitat types, three seasons, and two water levels. Results show that the combination of bank habitat type and section determines the habitat quality thus also determines the assemblage of fish species. Comparison with historical data and the pre-dam reference condition (Leitbild) reveals changes in species diversity/abundance over the past 40 years. The findings underscore the critical need for large-scale conservation and restoration measures to preserve fish biodiversity in regulated large river systems.

Riverine floodplains support diverse amphibian communities by providing essential habitats, with lateral hydrological connectivity (LHC or hydrology) determining local environmental conditions. Our study evaluated the direct and indirect effects of LHC on the two most abundant species in a riverine floodplain. We assessed the relative abundance of water frogs (Pelophylax spp.) and common toads (Bufo bufo) using eDNA surveys at 30 sites along an LHC gradient in the Danube River floodplain. We examined the habitat structure, vegetation cover, and the physical and chemical characteristics of waterbodies. Structural equation models (SEM) were used to explore LHC’s direct and indirect effects, mediated by these environmental factors. Results showed that LHC did not directly influence Pelophylax spp. and B. bufo abundance but affected them indirectly and species specifically through environmental drivers. Hydrology negatively and indirectly impacted Pelophylax spp. through vegetation cover and the physical and chemical properties of waterbodies. B. bufo was affected in a similar way but primarily through habitat structure. Our findings highlight the importance of understanding species-specific responses to lateral hydrological connectivity in dynamic environments, as river regulation altering LHC can differentially impact amphibian species in riverine floodplains.

The Danube River Basin (DRB) harbors the highest documented fish species richness of any European river, yet native populations face increasing threats from physical infrastructures that impede longitudinal and lateral connectivity, unsustainable fisheries, the introduction of non-native species, and climate change. Spanning across 19 countries, the DRB presents conservation challenges that demand coordinated, transboundary data sharing. The present database compiles and standardizes fish occurrence datasets that have been previously unavailable, fragmented and often restricted by federal agencies, research institutes, and conservation organizations, integrating also data from sources such as the Global Biodiversity Information Facility, the Joint Danube Surveys, the European Fish Index, and national monitoring programmes. It contains 133,131 occurrence records across 114 fish species, representing 30 families and 17 orders, with a temporal range from 1856 to 2024, organized into 39 columns. By supporting fish community conservation, invasive alien species monitoring, and climate impact assessments, this database provides a vital resource for developing evidence-based management strategies in the DRB.

Rivers and floodplains offer a plethora of Ecosystem Services (ES) in their natural state. However, various human interventions have altered their connectivity that drives ES supply, affecting the Multifunctionality of these aquatic ecosystems. In recent decades, various efforts have been made to restore connectivity among riverine ecosystems to bring back lost ecosystem functions and thus the ES they provide. This research offers fresh insights into how ES supply, their synergies and trade-offs, and Multifunctionality vary across three different Restoration Approaches that aim to reconnect rivers with their floodplains under different underlying conditions. They are classified as the National Park Approach (NPA), the Transformative Approach (TfA), and the Transboundary Approach (TbA), adopted in restored sections of the Danube and its two tributaries, the Traisen and the Morava, respectively. Based on when these measures were implemented, two time steps (2012 and 2020) were chosen to assess the pre- and post-conditions. Using various indicators to quantify ES, their distribution and degree of change, along with patterns in their synergies and trade-offs, were assessed for each approach. Results show that restoration impacts are most immediate for Regulating ES, followed by Cultural ES. Additionally, small-scale measures are sufficient in ecologically intact systems, whereas heavily regulated systems require large-scale measures, which are only possible through stakeholder collaboration. However, such large-scale measures create significant synergies and trade-offs, especially between Regulating and Provisioning ES. Thus, the socio-ecohydrological lens adopted with these three Approaches enabled this research to assess various underlying patterns of restoration measures targeting connectivity.

Flüsse, Auen und ihre Grundwasserkörper gehören zu den artenreichsten, ökologisch bedeutsamsten und gesellschaftlich unverzichtbarsten Ökosystemen Europas. Zugleich gehören sie zu den am stärksten bedrohten Ökosystemen. Um den zunehmenden multiplen Belastungen durch Klimawandel, Landnutzung, Schadstoffeinträge und Habitatverlust wirksam zu begegnen und nachhaltige Nutzungsperspektiven sicherzustellen, sind integrierte, langfristige Beobachtungsansätze dringend erforderlich. Dieser Artikel stellt DANUBIUS-ERIC vor, die seit 2025 als „European Research Infrastructure Consortium“ formalisierte europäische Forschungsinfrastruktur für Fluss-Meer-Systeme, und beschreibt die österreichische Forschungs-Supersite „Upper Danube Austria“ als einen ihrer zentralen Standorte. Die Supersite umfasst zwei komplementäre Forschungsgebiete: die Donauauen östlich von Wien (Nationalpark Donau-Auen) und das Ybbs-Einzugsgebiet. Die Supersite hat auf mehreren Ebenen Messinfrastruktur bestehend aus stationären Langzeitmessstationen in beiden Forschungsgebieten, mobilen Feldmessgeräten und Laborinfrastruktur aufgebaut, die eng mit dem gesamten europäischen Netzwerk verbunden sind. Erste Anwendungsbeispiele illustrieren das thematische Spektrum der Supersite: von der integrativen Grundwasserökologie und der Kohlenstoff- und DOM-Dynamik in Auengewässern bis zur einzugsgebietsweiten Modellierung von PFAS-Transportprozessen. Die Infrastruktur ist explizit auf die Unterstützung naturbasierter Lösungen, Renaturierungsmaßnahmen, nachhaltige Nutzungsansätze sowie die Umsetzung der EU-Wasserrahmenrichtlinie sowie des EU-Renaturierungsgesetzes ausgerichtet und ergänzt die bestehende behördliche Gewässerüberwachung um ökologische, biogeochemische und hydromorphologische Dimensionen, für die bislang keine systematische Langzeiterfassung bestand.

Headwater streams in tropical highlands provide critical ecosystem services by supporting biodiversity, regulating nutrient and carbon cycles, and maintaining water quality in downstream ecosystems. However, their strong dependence on surrounding landscapes makes them highly vulnerable to anthropogenic disturbances, which can have detrimental effects on their structure and functioning. Stream metabolism is a key indicator of ecosystem functioning, but its drivers in tropical highland streams remain poorly understood. To investigate these drivers, gross primary production (GPP) and ecosystem respiration (ER) were quantified across 11 anthropogenically impacted headwater streams in Uganda over a seven-month period, assessing the influence of proximal (in-stream) and distal (landscape) factors across various spatial scales. GPP was primarily limited by light, with turbidity reducing production in high-elevation streams and canopy cover limiting production in low-elevation sites. ER, on the other hand, increased in response to stream size and nutrient-rich sediments from steep, anthropogenically disturbed slopes. Overall, the combined effects of anthropogenic activities (agriculture, bare land, and built-up areas) and topography (elevation and slope) strongly influenced stream metabolism at distal scales. Landscape drivers affected metabolism indirectly through their impact on proximal factors, with topography often overriding anthropogenic effects. GPP was far lower than ER, as is typical for most tropical headwater streams. However, net heterotrophy in our study was primarily controlled by total suspended solids (TSS) rather than by commonly reported drivers such as terrestrial organic matter inputs and riparian shading. These findings suggest that climate-driven extremes, such as intense precipitation, are likely to amplify net heterotrophy in anthropogenically impacted tropical highland streams, with cascading effects on carbon cycling, water quality, and ecosystem functioning.

Introduction River regulation schemes generally led to changes in riverine assemblage composition and their trophic status, which often is reflected in a general loss or decrease of characteristic species and a concomitant increase or dominance of generalist species.Objectives This study examines changes of the hydrodynamic conditions, plankton biomass as well as changes in feeding guilds and the assemblages of macrozoobenthos and of fishes before and after the re-connection of a sidearm of the main stem in a free-flowing section of a large river (Danube in Austria).Methods In order to analyze the effects in the sidearm, a before-after control-impact design was applied; a river section in the main stem served as a reference site.Results The higher and increased connectivity had sizable effects on hydraulic parameters, with the expected shift of prevailing lentic to year-round lotic conditions in the sidearm. The composition of suspended solids changed significantly. Likewise, chlorophyll-a concentrations and zooplankton abundance decreased markedly. The new conditions in turn modulated the pathways and the structure of the food web.Conclusions The permanent flow-through in the sidearm decreased the importance of detritus and forced the one of periphyton and biofilm as an energy and nutrient source for insect larvae which also affected higher trophic levels, that is, fishes.

Connectivity is a crucial property of the riverine landscape. Reduction of connectivity, i.e. habitat fragmentation and isolation effects, impacting ecological functions and biotic communities, is one of the most critical threats to river-floodplain systems. Using a graph theoretical approach for analyzing possible transport pathways in the system (directed, undirected, overland, seepage), we could show that essential ecological functions related to sediment composition and quality, hydrochemical conditions, and macrophyte coverage can be predicted and importance of waterbodies in the network and their main connectivity deficits can be identified. In a second step we are now integrating biotic communities in the predictive framework. Dependent on dispersal model and habitat preferences the different taxonomic groups show clear pattern i.e. drifting invertebrate organisms are highly driven on directed transport whereas fish as active swimmers are more dependent on connectivity in the waterbody network or organism with terrestrial or flying dispersal (amphibia or flying insects) are dependent on overland connectivity. Further they interact with the ecological functions in the system. Using a temporal dataset based on eDNA (environmental DNA) we can further show that ecosystem conditions and distributions of biotic communities are dependent on different transport/movement pathways changing with hydrological conditions (flood to low flow conditions). The dynamic graph theoretic approach can, therefore, be used as an essential tool for prioritizing water bodies for nature-based solutions.

African highlands provide important ecosystem services, supporting >80 million people, with >65 % relying on agriculture in highland valley-bottom wetlands (HVBW). These wetlands have been overlooked in inventories because of their small size, agricultural conversions, management practices, and deforestation. Using remote sensing, interviews, and observations, this study considered the drivers of land use and land cover change in HVBW in Taita Hills, Kenya. We inventoried agricultural and water management practices to understand the impact on ecosystem services and synthesized the information using the DPASER framework (Drivers, Pressures, Actions, State of the ecosystem, Ecosystem services, and Responses). We show that HVBW can be delineated using high-resolution (5 m) Digital Terrain Models (DTM) and the Multiresolution Valley Bottom Flatness (MrVBF) index, and validated with a Normalized Difference Moisture Index (NDMI2) and ground-truthing. HVBW are intensively used by smallholders for cropland and agroforestry. Most conversions occurred more than 50 years ago with the Land Adjudication Act of 1968 but increased from 88 % to 93 % from 1987 to 2023, respectively. Other drivers of wetland degradation include population growth, poverty, climate variation, and food insecurity resulting in more intensive year-round agriculture. To sustain HVBW ecosystem services including carbon storage, biodiversity, and water provisioning, we recommend collaborating with farmers through local organizations to identify and preserve abandoned flooded HVBW as natural systems, and to implement regenerative agriculture in mixed farming systems. Existing policies regarding forests, wetlands, and agricultural management should be harmonized and enforced to promote the use of native and indigenous trees.

Natural wetlands are critical water quality regulators, especially in developing tropical countries. The Lubigi wetland is a large urban wetland in Kampala, the largest city in Uganda in Africa. We studied whether stormwater discharge and wastewater effluent from a nearby stormwater channel and a sewage treatment plant in the western part of the city were cleaned as they flowed through the wetland. Despite the significant pollution, the wetland removed ammonium-nitrogen, orthophosphate, and particulate nutrients during both seasons, achieving removal rates ranging from 50 to 60% for orthophosphate but only 20–40% for ammonium-nitrogen. Overall, seasonal differences in loads and retention rates of nutrient and organic matter inputs were minimal. Interestingly, the wetland mostly released nitrate and nitrite during water passage through the wetland, most likely due to the mineralization of organic nitrogen and agricultural run-off during rainy events in the wet season. However, the limited capacity of the sewage treatment plant and untreated stormwater discharge from the Nsooba main channel reduced the wetland’s ability to clean water. The insufficient carrying capacity of the treatment plant and the release of untreated sewage into the wetland significantly impact the self-purification capacity of the Lubigi wetland. Thus, the concept of Nature-Based Solutions is ineffective if the wetland systems are overloaded.