Fish migration through river networks is essential for completing life cycles and accessing critical habitats, but fragmentation increasingly disrupts spawning movements. In Europe, over one million barriers limit connectivity and create trade-offs between ecological integrity and human uses, such as hydropower, flood control, fisheries and water storage. Furthermore, climate change can decrease habitat suitability, reinforcing migration needs to escape local extinctions. Limited knowledge of environmental triggers constrains species-specific migration predictions. Here, we quantified the influence of seven environmental triggers-water temperature, flow, turbidity, cloud cover, rain, air pressure and radiation-on spawning migration of European freshwater fishes. A meta-analysis of 112 studies (685,333 individuals, 953 effect sizes, 50 species) showed that water temperature was the dominant migration trigger. Radiation, turbidity and cloud cover showed weaker, context-dependent effects, while effects of flow, rain and air pressure were non-significant. Species-specific average spawning migration temperatures correlated with upper limits of species-specific thermal tolerances, indicating that migration timing reflects physiological constraints. Following this argument, we derive a new classification of thermal sensitivity for European freshwater fishes, distinguishing three thermal spawning guilds: cold (< 11 degrees C), cool (11 degrees C-15 degrees C) and warm (> 15 degrees C), with positive migration responses to temperature most frequently in warm-water, less in cool-water and rarely in cold-water species. Our synthesis identifies gaps for species and triggers beyond temperature and flow, providing a quantitative basis for predicting spawning migration timing to guide conservation and connectivity restoration in European rivers.

Freshwater biodiversity is experiencing dramatic declines. Despite improvements, the trend remains negative, underlining that effective and coordinated initiatives are needed. Protected areas are considered a global cornerstone of biodiversity conservation, and in Europe, the Natura 2000 network plays a central role in safeguarding biodiversity. In the present study, we examine if designated Annex I listed freshwater habitats of the Habitats Directive are sufficiently represented to enable conservation and restoration efforts, as outlined in Article 4 of the European Nature Restoration Law (NRR), to meaningfully contribute to reversing the ongoing decline in freshwater biodiversity. Additionally, we examine whether freshwater habitats are represented across their full natural geographical range, addressing a key spatial component of long-term persistence, as reflected in the concept of "favorable reference area" as defined in Article 3 of the NRR. We found that freshwater habitats cover 6.2% of the total area of Natura 2000 sites with running waters covering only 0.4%. In addition to a low spatial coverage, the analyses also indicated that several freshwater Annex I habitats are not represented across their full natural geographical range. Based on the obtained results, we therefore argue that a systematic strengthening of the Natura 2000 network is required, with particular emphasis on: (1) expanding the extent of designated freshwater habitat types in- and also outside the existing network if necessary to adequately cover freshwater habitats, and (2) identifying and addressing representation gaps across all relevant biogeographic regions. To support this process, we have developed a webtool based on the datasets underlying the analyses, which enables relevant stakeholders including EU institutions, national agencies, and local managers to examine the distribution of freshwater habitats and species protected within the current Natura 2000 network. The webtool can be accessed at https://www.waterwebtools.com/merlin.

The EU’s Nature Restoration Regulation has created unprecedented momentum for ecosystem restoration. Its success now depends on translating ambitious targets into spatially coordinated restoration landscapes supported by effective governance, long-term financing and broad societal engagement.

Climate change is intensifying hydrological variability in streams, but organism groups may respond to different environmental pathways associated with low-flow and high-flow conditions. We assessed how hydrologically relevant environmental gradients were associated with five biological response groups (diatoms, macrophytes, herbaceous riparian vegetation, macroinvertebrates and cotton-strip decomposition) in perennial lowland streams in Germany. Predictors included shear stress, nutrient concentrations (total N, total P, DOC), water temperature, solar radiation, shading and elevation above water level. Community composition and functional metrics were analysed using Canonical Correspondence Analyses and regression models. Predictor associations varied among groups, with macrophytes showing the highest explained variance (42%) and riparian vegetation the lowest (10.1%). Macrophyte composition was mainly associated with shear stress and total N, while diatom assemblages were most strongly associated with solar radiation. Riparian vegetation reflected local light and moisture gradients, with shading and elevation above water level correlated with Ellenberg indicator values. Macroinvertebrate metrics were associated with shear stress, total P and temperature, while cotton-strip decomposition increased with DOC and maximum temperature. Overall, our results indicate organism-specific sensitivity pathways rather than uniform responses to hydrological variability. Multi-taxa assessments can therefore help identify which environmental gradients and ecosystem components are most relevant for anticipating ecological responses to climate-driven hydrological change.

english abstract see below Digitale Anhänge (Version 2) zu BfN-Schriften 655 "Biozönotische Erfolgskontrolle von Renaturierungsmaßnahmen an Gewässerufern und in Auen" Die digitalen Anhänge zur "Biozönotischen Erfolgskontrolle von Renaturierungsmaßnahmen an Gewässerufern und in Auen" sind Excel-Vorlagen (incl. Testdatensätzen und Erläuterungen) zur Dateneingabe und Berechnung von Kenngrößen für die Bewertung der Habitatausstattung sowie der Artausstattung für die Artengruppen Amphibien, Gefäßpflanzen, Land- und Wassermollusken, Laufkäfer und Vögel. Beim Vergleich zweier Ufer- bzw. Auenabschnitte wird die Differenz ermittelt. Die BfN-Schriften 655 sind unter folgender DOI abrufbar: 10.19217/skr655 Zusammenfassung der BfN-Schriften 655 Vor dem Hintergrund zahlreicher umgesetzter und geplanter Renaturierungsmaßnahmen an Fließgewässern und deren Auen steigt der Bedarf an einer standardisierten Bewertung und Erfolgskontrolle, die die „biologische Wirksamkeit“ von Renaturierungen im Hinblick auf unterschiedliche Zielvorstellungen messbar und sichtbar machen. Im Gegensatz zu einheitlichen Verfahren für die Fauna und Flora in Fließgewässern (z.B. Monitoring aquatischer Artengruppen nach Wasserrahmenrichtlinie sowie Verfahrensempfehlung zur Erfolgskontrolle hydromorphologischer Maßnahmen) sind die biologischen Bewertungsansätze für Ufer und Auen bundesweit sehr heterogen. Bestehende Bewertungssysteme, wie z. B. das Monitoring der Fauna-Flora-Habitat-Richtlinie (FFH-Richtlinie), geben zwar einen Einblick; allerdings erfolgt das Monitoring ausschließlich in Schutzgebieten auf der Ebene von Lebensraumtypen und ausgewählten Arten. Im Hinblick auf die hohe Artenvielfalt in Auen steht hier eine vergleichsweise geringe Auswahl an Tier- und Pflanzenarten zur Verfügung. Somit fehlt ein bundesweiter Ansatz für die Zustandsbewertung der Lebensgemeinschaften an Ufern und in Auen sowie Möglichkeiten einer einheitlichen Erfolgskontrolle. Mit dieser Veröffentlichung wird ein einfach anwendbares, standardisiertes Verfahren vorgestellt, mit dem Akteure den Erfolg von Renaturierungsmaßnahmen für Flora und Fauna an Ufern und in Auen nachvollziehbar bewerten können. Das Verfahren berücksichtigt die Artengruppen Amphibien, Gefäßpflanzen, Land- und Wassermollusken, Laufkäfer und Vögel. Die Bewertung erfolgt leitbildgestützt auf Grundlage von Auenschlüsselhabitaten und Indikatorarten. Für 18 bundesweit beschriebene Abschnittstypen der Fluss- und Stromauen Deutschlands wurden zunächst Leitbilder zur Habitat- und Artenausstattung (Auenschlüsselhabitate und Indikatorarten) als Grundlage für die Bewertung ermittelt. Die Bewertung kann in Bezug auf die Habitatausstattung und für die oben genannten Artengruppen mit Hilfe von biologischen Kenngrößen erfolgen. Drei obligate Kenngrößen bilden die wesentlichen Elemente einer biozönotischen Erfolgskontrolle: auenabschnittstypspezifische Indikatorarten, Arten mit starker Auenbindung und nach der Roten Liste Deutschlands gefährdete Arten. Darüber hinaus stehen weitere optionale Kenngrößen für die Bewertung zur Verfügung, wie z.B. Indikatorarten für ausgewählte Auenschlüsselhabitate oder nach Bundesartenschutzverordnung geschützte Arten. Für jede Kenngröße wurden die relevanten Arten aus allen bundesweit vorkommenden Arten der einzelnen Artengruppen ausgewählt und in Indikatorartenlisten unter Berücksichtigung von Standardwerken und unter Einbindung von Expertenwissen zusammengestellt. Für einen schnellen Überblick über die Auenabschnittstypen illustrieren biozönotische Steckbriefe die wesentlichen, standörtlichen und für die Lebensgemeinschaften relevanten Charakteristika. Für das methodische Vorgehen bei einer biozönotischen Erfolgskontrolle werden der Ablauf der Erfolgskontrolle, der Anwendungsbereich, mögliche Untersuchungsdesigns, die Grundprinzipien der Bewertung, die notwendigen Datengrundlagen sowie die konkreten Arbeitsschritte der Berechnung erläutert. Als Hilfsmittel für die Berechnung der Habitatausstattung und der Kenngrößen der genannten Artengruppen stehen den Anwender*innen Excel-Vorlagen mit Berechnungsformeln und Indikatorartenlisten für 12 Fluss- und 6 Stromauenabschnittstypen zur Verfügung, mit denen alle der 79 großen Flüsse und Ströme Deutschlands (Einzugsgebiet > 1.000 km2) sowie mit den Auenabschnittstypen vergleichbare Abschnitte an kleineren Flüssen abgedeckt sind. Die Erfolgskontrolle fußt auf einem Vergleich der Bewertungsergebnisse zweier Untersuchungsabschnitte (z.B. Vorher-Nachher-Vergleich eines Untersuchungsabschnitts, Vergleich renaturierter und stromaufwärts gelegener degradierter Vergleichsabschnitt („space-for-time“) oder BACI (= Before-After-Control-Impact). Die Berechnungen erfolgen dabei separat für jede Artengruppe und die einzelnen Untersuchungsabschnitte. Die Bewertung der Habitatausstattung erlaubt Aussagen darüber, ob und in welchem Maß auenabschnittstypspezifische Auenschlüsselhabitate als Voraussetzung für die Ausprägung von wertgebenden Lebensgemeinschaften vorhanden sind. Die Habitatausstattung ist dabei v.a. ein unterstützendes Hilfsmittel. Die Auswertung der biologischen Kenngrößen zeigt auf, inwieweit auenabschnittstypspezifische und wertgebende Pflanzen- und Tierarten in den Untersuchungsabschnitten vorhanden sind bzw. von einer Renaturierung profitiert haben; jedes Kenngrößen-Ergebnis steht separat zur Verfügung. Die Berechnung kann mit bereits erhobenen oder neu zu erfassenden Daten zu den jeweiligen Artengruppen erfolgen. Grundvoraussetzung ist, dass die Erfassung der Artengruppen in den beiden zu vergleichenden Untersuchungsabschnitten bzw. Erfassungsjahren nach derselben Methodik erfolgt ist. Veranschaulicht wird das Verfahren anhand eines Anwendungsbeispiels, das die Ergebnisse der Erfolgskontrolle und deren Interpretation exemplarisch auf Grundlage von Habitatdaten und Daten zu Gefäßpflanzen, Laufkäfern und Vögel eines renaturierten und eines stromaufwärts gelegenen, degradierten Abschnitts der Ruhr bei Arnsberg (Nordrhein-Westfalen) erläutert. Um zukünftig bundesweite Vergleiche von Bewertungsergebnissen möglich zu machen, wurden für jede Artengruppe Empfehlungen für standardisierte Erfassungsmethoden entworfen. Diese beschreiben einen einfachen und kostengünstigen Mindeststandard für eine biozönotische Erfolgskontrolle an Ufern und in Auen; sie stehen dabei nicht in Konkurrenz mit bestehenden Monitoringansätzen (z.B. FFH-Monitoring). Die artgruppenspezifischen Erfassungen orientieren sich an bekannten Methoden und sollen im Rahmen eines zukünftigen Praxistests erprobt werden. In diese Studie eingeflossen sind zahlreiche konstruktive Optimierungsvorschläge einer breiteren Fachöffentlichkeit (Naturschutz, Wasserwirtschaft, Behörden, freiberufliche Gutachter*innen, Wissenschaftler*innen, Verbände u.a.m.), die im Rahmen eines digitalen Workshops im März 2021 gesammelt wurden. Im Vorfeld des Workshops konnten die Teilnehmenden mit Hilfe von Erläuterungstexten, Excel-Vorlagen und Testdatensätzen für die Berechnung das Bewertungsverfahren testen und über interaktive Feedbackrunden und Meinungsumfragen auf dem Workshop ihre Erfahrungen mitteilen. Für die Zukunft haben sich eine Reihe von möglichen Fragestellungen und Ergänzungen zur biozönotischen Auenzustandsbewertung herauskristallisiert, die im Rahmen von weiteren Fallbeispielen umfassend von der Erfassungsmethodik bis hin zur Anwendbarkeit und Aussagekraft der biologischen Kenngrößen zu testen sind. Digital appendices (version 2) to BfN publication 655 “Biocenotic assessment of the success of renaturation measures on riverbanks and in floodplains” The digital appendices to “Biocenotic assessment of renaturation measures on riverbanks and in floodplains” are Excel templates (including test data sets and explanations) for data entry and calculation of parameters for the assessment of habitat conditions and indicator species for the species groups amphibians, vascular plants, terrestrial and aquatic mollusks, carabid beetles, and birds. When comparing two sections of a riverbank or floodplain, the difference is determined. BfN Publication 655 is available at the following DOI: 10.19217/skr655 Abstract of BfN Publications 655 Recently, rivers and their floodplains are increasingly subject to restoration measures. To rate restoration effectiveness, the demand for standardized methods to monitor and assess rehabilitation measures is increasing. Ideally, assessment methods should address the various objectives that drive restoration measures. While there are standardized methods for biotic assessment of rivers that are used for implementing the Water Framework Directive, there is a wide variety of approaches to assess riparian areas and floodplains. For instance, the approaches related to the European Birds and Flora- Fauna-Habitat Directives are exclusively used in Natura2000 areas and target particularly selected habitats and species. Accordingly, they address only a small fraction of the diverse floodplain biota. Against this background, there is the need for a standardized methodology to assess the status of riparian areas and floodplains, including quality assurance procedures. Here we introduce such a method that has been co-developed by stakeholders and is particularly designed to judge the effects of restoration measures on riparian and floodplain biota, i.e. vascular plants, terrestrial and aquatic mollusks, carabid beetles, amphibians, and birds. The new method is based on the occurrence of key floodplain habitats and indicator species. As a basis for assessment, we first defined reference conditions for key habitats and indicators species of 18 floodplain types. Assessment options include a screening based on habitat conditions and a more detailed analysis based on the aforementioned organism groups. For the latter, the assessment is composed of three mandatory elements: indicator species of the floodplain type, more generally defined floodplain-specific species, and endanger

A multitude of anthropogenic stressors drive biodiversity loss and alter ecosystem functioning. Freshwaters, which contribute disproportionally to global biodiversity and biogeochemical cycles, are particularly threatened. Although the relationship between biodiversity and ecosystem functions (BEF) is generally well-established, especially in terrestrial ecosystems, the role of multiple, co-occurring stressors in modulating the relationship remains unclear. We conducted a meta-analysis to address this knowledge gap by assessing the effect of multiple stressors on the relationship between taxon richness and four measures of ecosystem function. The relationship was generally positive, with the slope becoming steeper as the number of stressors increased, suggesting that exposure to multiple stressors exacerbates impacts of biodiversity loss on ecosystem function. Multiple stressor effects on both taxon richness and ecosystem functions were largely predictable from individual stressor effects, although antagonistic effects on ecosystem functions emerged in 14% of the considered cases. The type of stressor and ecosystem function, along with taxonomic group, exerted no influence on the BEF relationship, contrary to our expectations. Microbial production and biomass declined most strongly in response to stressors, despite notable variability. Overall, our findings imply that functional consequences of freshwater biodiversity loss are more severe under multifaceted environmental change than previously assumed.

Understanding the temporal development of community assembly processes is essential for assessing the recovery of degraded ecosystems after restoration. Community development in restored streams is often slow or absent, due to inadequate restoration, catchment-scale pressures, and/or colonisation barriers. Recovery processes involve three key filters: dispersal, environmental conditions and biotic interactions. Dispersal is critical for initial colonisation, while environmental conditions influence successful population establishment. Lastly, as available niches fill, biotic interactions, such as competition, gain importance. Despite the presence of many theories on how these three filters interact during community assembly, they have rarely been investigated simultaneously. Our detailed species- and site-specific approach allowed us to analyse the three filters in a hierarchical analysis. We assessed the effect of the three filters, by examining benthic invertebrate communities at 20 sites in the Boye catchment (Western Germany). The Boye and most of its tributaries were used as open sewers for a century, i.e. they were concrete channels transporting untreated sewage before gradual restoration was started in the 1990s. The bank reinforcements and concrete beds were removed, while riparian vegetation was left to natural succession. Accordingly, the sites were grouped as 'unimpacted', 'recently restored' (< 4 years), and 'mature restored' (> 10 years). An additional 28 sites provided information on distances to source populations, while the species’ habitat suitability assessed environmental filtering. Biotic (interaction) filtering was evaluated through trait overlap analysis. Communities at recently restored sites differed from mature and unimpacted sites, while mature sites resembled unimpacted ones. Taxa at recently restored sites had nearer source populations, while those at mature and unimpacted sites better matched present habitats. Trait overlap did not differ between present and absent taxa. Our results indicate that dispersal was essential in early recovery stages, with mass effects from upstream sources supporting taxa found at recently restored sites despite low habitat suitability. Over time, habitat suitability became more influential, shaping mature communities. Competition appeared relatively unimportant, yet competitive exclusion may explain small proportions of absent taxa at mature and recently restored sites. Hence, to effectively support stream recovery, it is essential to consider how different filtering processes operate at various stages of the recovery process. For example, mature communities could further develop if habitat availability increases, while the connectivity to source populations would only play a minor role.

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.

The global freshwater biodiversity crisis has led to widespread implementation of measures to counteract environmental degradation and biodiversity loss. While these efforts aim to foster recovery, intensifying stressors continue to drive complex biotic responses, the trajectories and drivers of which are insufficiently understood. This study examines the roles of abiotic stressors, biotic interactions (e.g., competition), and land use in shaping ecological status changes across Germany, using data from 1599 river sites sampled at least twice between 2004 and 2022. Changes in abiotic stressors emerged as the most consistent drivers of ecological status, explaining substantial variation (R2 = 0.39) and similar slopes for recovery (β = − 0.11) and degradation (β = − 0.10). Biotic interactions, particularly interspecific competition, also influenced the ecological status (R2 = 0.11), with stronger positive effects observed during recovery (β = 2.99) compared to degradation (β = 1.59). Land use effects varied by context: Streams in catchments with higher cropland or urban areas showed greater likelihood of recovery, whereas streams in forested catchments were more prone to degradation. These results highlight the interplay of abiotic and biotic factors in driving ecological processes of recovery and degradation. These findings emphasize the critical role of improving water quality for enhancing biodiversity and ecological status in rivers, while also demonstrating the importance of biotic interactions and land use context in driving recovery dynamics. Integrating these insights into management and restoration efforts can enhance freshwater ecosystem resilience in the face of escalating environmental pressures.

Unmulched lawns in cemeteries in the western Ruhr area are characterised by an exceptionally high species richness of over 400 vascular plant species in total. 242 species were recorded in vegetation releves with up to 34 plant species in a survey area of 8 m(2) (9 m(2) area size was aimed for as standard). In addition, a total of 38 species occur in all the releves that are on the federal state or regional Red List, with up to six species occurring in individual releves. Particularly noteworthy is the occurrence of some rare species belonging to the arable flora, sandy grassland and heathland vegetation. The association of these species could also be documented phytosociologically by vegetation releves on the cemetery lawns. Some of these areas are located in cemeteries in the centre of urban agglomerations, where they have been preserved as relics of a pre-industrial landscape. In addition, typical lawn vegetation from the Crepido-Festucetum association was recorded in many of the cemeteries, but a fragment community was also differentiated, which was essentially created by mulching the lawns.The vegetation of non-mulched cemetery lawns varies considerably depending on altitude, soil type, cemetery age and burial use in the surrounding of the plot. Mulched areas, however, have a highly uni-form species composition. Not only are they floristically impoverished and Red List species are largely absent, they also form a homogeneous unit without regional or area-specific differences. Their flora consists of a few grasses and undemanding ubiquists. Against this background, a switch to mulching should be avoided at all costs, especially on the remaining areas of high floristic value

The ecological state of aquatic ecosystems is systematically monitored using various bioindicators in many countries worldwide. In the European Union, freshwater biomonitoring is the central component of the EU Water Framework Directive (WFD, 2000/60/EC) and currently based on morpho-taxonomic methods. DNA metabarcoding is a novel approach to assess the ecological state fast and efficiently based on organismal DNA signatures and thereby support and upscale biomonitoring. However, compliance of metabarcoding with existing morpho-taxonomic methods must be ensured prior to official implementation. Thus, this study co-designed by research institutions and environmental agencies explored necessary key parameters and performed method intercalibration for the implementation of metabarcoding into WFD assessments of running waters. We focussed on benthic invertebrates as the most commonly used bioindicators. We analysed 170 invertebrate samples collected as part of the German federal state WFD routine stream biomonitoring, first via microscopic determination and then using metabarcoding. Our goals were to quantify overlap in i) taxonomic composition and ii) ecological status derived with both methods. For this purpose, we established data harmonisation measures to integrate invertebrate metabarcoding data into the official national WFD classification modules considering abundance and presence/absence data. Our results revealed a high (ca. 70%) overlap of bioindicator taxa found with both methods. Metabarcoding identified significantly more small invertebrate taxa and detected similar proportions of the important bioindicator ‘EPT’ taxa (mayflies, stoneflies, caddisflies). Despite deviations in some detected bioindicator taxa, the derived ecological status classes were highly correlated between methods, particularly after intercalibration (R2=0.74, Spearman rho=0.86). Regardless of whether we used abundance or presence/absence data, the resulting stream type classifications showed strong agreement. Thus, our study not only demonstrates the consistency of the methods for the stream types analysed but is also the first to operationalise a path to integration of metabarcoding data into the WFD assessment modules based on formal intercalibration guidelines.

We investigated the role of woody riparian vegetation (WRV) in reducing the detrimental effects of extreme low-flow conditions on macroinvertebrate communities in Central European streams. We hypothesized that WRV decreases water temperature, thereby lessening the impacts of drought on streams. The study was conducted in the Lippe catchment in northwestern Germany at 26 study sections during the summer drought of 2022. Water temperature and macroinvertebrate communities were analyzed. WRV cover, groundwater influx, cross-section form and flow velocity were considered as predictors in structural equation models. We investigated how the immediate effects of extreme summer low-flow on water temperature and macroinvertebrates were mitigated by the four predictors. Shading by WRV and groundwater influx caused a significantly lower mean daily maximum water temperature of 6.6 °C and 4.8 °C, leading to a higher share of stream-type specific and temperature-sensitive macroinvertebrate taxa and feeding types typical for rhithral stream reaches. These results indicate that both WRV and groundwater influx play a crucial role in regulating stream temperature and maintaining stream-type specific macroinvertebrate communities under extreme low-flow conditions. The study highlights WRV management as a key tool for protecting stream ecosystems from the increasing frequency of droughts and related low-flow due to climate change.

When rivers are dammed or incised, the adjacent floodplains are often hydrologically decoupled from the river, with potentially drastic impacts on terrestrial biotic communities. Morphological river restorations are not always successful in restoring biodiversity, but causes remain obscure. A better understanding of the association of river-floodplain connectivity and floodplain biota is therefore necessary. We compared diversity and composition of plant, mollusc, and carabid (ground beetle) communities from coupled and decoupled floodplain sections along the Elbe River to investigate how they are affected by floodplain decoupling. Our analyses include both taxonomic and functional diversity indicators based on traits that reflect how well-adapted species are to flood disturbance. We recorded a total of 202 plant species, 146 carabid species, and 41 mollusc species. Plants and molluscs showed lower species richness and lower shares of indicator species for periodically wet grassland in the decoupled sections, while these metrics were higher for carabids. Abundance of species adapted to high disturbance was lower for molluscs in the decoupled floodplain sections, indicating that communities in these sections are less adapted to near-natural disturbance regime, while this metric, again, was higher for carabids. Functional richness, i.e., the volume of multidimensional trait space occupied by a community, decreased in the decoupled floodplain section for all three organism groups. Our results underscore the complex responses of different organism groups to differences in river-floodplain connectivity and suggest that floodplain specialist species of less mobile groups are disproportionately negatively affected by floodplain decoupling, contrary to the flight-active carabids. To capture community dynamics and to ensure maximum efficiency of restoration and conservation activities, a variety of organisms and aspects of biodiversity (taxonomic and functional) needs to be considered.

Freshwater ecosystems, particularly rivers, are experiencing the most rapid biodiversity declines of any biome, driven by several interacting stressors operating across local to global scales. Despite growing research on these interactions, the lack of systematic quantification of individual stressor gradients limits our ability to disentangle their cumulative effects. Here we present a global synthesis of stressor–response relationships across five key riverine organism groups—prokaryotes, algae, macrophytes, invertebrates and fish. We screened 22,120 papers and extracted 276 studies with 1,332 stressor–response relationships. We used generalized linear mixed models and Bayesian meta-analyses to quantify the response to the seven most prevalent stressors. Consistently across taxa, biodiversity loss (taxon richness and evenness) reflected elevated salinity, oxygen depletion and fine sediment accumulation, while the association with nutrient enrichment and warming varied among groups. Predictive tools, including hypothetical outcome plots and partial dependence plots, revealed the interplay of stressors and predicted biodiversity response to stress increase. Our findings establish a quantitative baseline for a continuous global synthesis, refining predictions of anthropogenic stressor impacts, identifying key research gaps and informing conservation strategies for freshwater ecosystems.

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.

Halting biodiversity loss, mitigating global warming and maintaining the long‐term viability of rural and urban areas requires urgent policy action. However, environmental policies often trigger resistance and highly polarised public debates, with some actors employing pseudo‐scientific claims. This raises concern about the increasing impact of misinformation on policymaking. Here, we analyse the role of science and scientists in the public debate around two pieces of legislation that were proposed in 2022 by the European Commission as part of the Green Deal, namely the Nature Restoration Regulation (NRR) and the Sustainable Use Regulation (SUR) of plant protection products. First, we examine key claims against these two legislative proposals and contrast them with scientific evidence. We show that these claims fail to consider ample scientific evidence that restoring nature and reducing the use of agrochemicals are essential for maintaining long‐term agricultural production and enhancing food security. Critics further failed to acknowledge that the NRR and SUR may generate new employment opportunities and stimulate innovation, with high return rates and multiple beneficiaries across society, fostering a transition to sustainable production and consumption models. Second, we examine how the publication of an open letter, signed by 6000 scientists, may have influenced the public debate. We contrast the role that scientific evidence played in the fate of the NRR, which was adopted, against the fate of the SUR, which was rejected by the European Parliament. We draw lessons from these two cases that illustrate the global tension between environmental protection and economic‐driven interests to spread misinformation. We argue that scientists should play an important role in making scientific evidence more accessible and available to the general public and policymakers for informed decision‐making. We recommend that scientists be proactive and unbiased in providing information and data and that policymakers use scientific evidence and engage scientists in developing much needed, well informed environmental policies. Read the free Plain Language Summary for this article on the Journal blog.

Beaver activities modify floodplains of small streams fundamentally. Prevailing lotic sections are supplemented with several additional habitats (e.g., ponds, dams and side channels). While there are several investigations into the invertebrate fauna of single beaver-induced habitats, the ways beavers modify aquatic invertebrate assemblages of entire floodplain sections have not been explored. We investigated three beaver territories and three upstream floodplain sections ("non-beaver territories"). We quantified the areas covered by different aquatic habitat types and collected 188 habitat-specific invertebrate samples that yielded more than 82,000 individuals. We used GLMMs with logit links and PCoA to quantify the differences between territory types in terms of aquatic habitat area, abundance, species richness, general community composition, and flow preferences. The area of aquatic habitats increased six-fold in beaver territories. The abundance of benthic invertebrates increased by a factor of 4.5. From species extrapolation analysis, we inferred that species richness in beaver territories increased by factor of 2.7, compared to non-beaver territories. Of the 254 taxa recorded, 141 occurred exclusively in beaver territories and only four taxa occurred exclusively in non-beaver territories. The most taxa-rich habitat type was side channels in beaver territories. Community composition was most similar between habitat types with comparable flow patterns (e.g., beaver ponds and pools in non-beaver territories). In both territory types, rheophile taxa accounted for the largest percentage, with a median of 57% in beaver territories and 61 % in non-beaver territories. The number of rheobiont taxa (21 in total) was higher in beaver territories (20 taxa) than non-beaver territories (16 taxa), while the overall proportion of rheobiont taxa was higher in non-beaver territories. Beaver activities greatly enhanced species richness and abundance of aquatic invertebrates. While a predominantly lotic community shifts to an assemblage with more heterogeneous flow preferences, almost no taxa (not even those dependent on high currents) were eliminated from beaver territories. Beavers thus enhance aquatic invertebrate biodiversity while maintaining the original community. Beaver activities are cost-effective means by which the biodiversity of small floodplains can be enhanced and should be an integral part of restoration plans in regions where beavers were formerly present.

Humans impact terrestrial, marine and freshwater ecosystems, yet many broad-scale studies have found no systematic, negative biodiversity changes (for example, decreasing abundance or taxon richness). Here we show that mixed biodiversity responses may arise because community metrics show variable responses to anthropogenic impacts across broad spatial scales. We first quantified temporal trends in anthropogenic impacts for 1,365 riverine invertebrate communities from 23 European countries, based on similarity to least-impacted reference communities. Reference comparisons provide necessary, but often missing, baselines for evaluating whether communities are negatively impacted or have improved (less or more similar, respectively). We then determined whether changing impacts were consistently reflected in metrics of community abundance, taxon richness, evenness and composition. Invertebrate communities improved, that is, became more similar to reference conditions, from 1992 until the 2010s, after which improvements plateaued. Improvements were generally reflected by higher taxon richness, providing evidence that certain community metrics can broadly indicate anthropogenic impacts. However, richness responses were highly variable among sites, and we found no consistent responses in community abundance, evenness or composition. These findings suggest that, without sufficient data and careful metric selection, many common community metrics cannot reliably reflect anthropogenic impacts, helping explain the prevalence of mixed biodiversity trends.

Intensive agriculture drives an ongoing deterioration of stream biodiversity and ecosystem functioning across the planet. Key agricultural stressors include increased deposited fine sediment and insecticides flushed from adjacent land into streams. The individual and combined effects on aquatic biota are increasingly studied, but the functional consequences of biodiversity loss associated with agricultural stressors remain poorly understood. We addressed this knowledge gap by examining the effects of fine sediment and different concentrations of the insecticide chlorantraniliprole on organic-matter decomposition.We conducted an outdoor stream mesocosm experiment. Mesocosms contained a standardised organic-matter assay (the cotton-strip assay), which was used to assess organic-matter decomposition rates (as tensile-strength loss of the fabric) and microbial respiration of the cotton strips.The decomposition rate of strips buried under fine sediment was inhibited, a result we attribute to the limited accessibility for invertebrate feeding and microbial activities, as well as the limited nutrient and dissolved oxygen exchange. The insecticide also inhibited decay rates, a finding we relate to reduced invertebrate grazing and associated excessive algal growth. In contrast to decomposition rates, we did not observe stressor effects on microbial respiration. An interaction between fine sediment and chlorantraniliprole was not identified.Our results suggest that stressors induced by agriculture affect functions of stream ecosystems through a variety of pathways and operate by modifying habitats and biotic interactions.By examining a combination of stressors and responses that have not been addressed before, this study gives important insights into the effects of agricultural practices on streams. Understanding the effects of chlorantraniliprole is especially important since it is likely to become more widely used in future agricultural practice due to the increasing ban on neonicotinoid insecticides. Furthermore, most experimental studies address multiple stressor effects on biota. For a comprehensive understanding of complex stressor effects on ecosystems, ecosystem functions also need to be studied, such as the organic-matter decomposition within streams.

Community development in restored streams is often slow or even absent, but reasons remain obscure. Inadequate restoration measures, catchment-scale pressures, community closure and colonization barriers all may prevent or slow down recovery processes. For initial colonization, dispersal processes are supposed to be most important, which are referred to as dispersal filter. Environmental conditions of a restored reach determine if a dispersing species can successfully establish (environmental filter). Lastly, while available niches at those reaches fill up, biotic interactions, such as competition, become more important (biotic filter). To investigate the importance of these different filters, we compared benthic invertebrate communities of 20 sites in the Boye catchment (Western Germany), a former open sewer system. The sites were grouped, based on the years since restoration, into ‘unimpacted’ (never restored), ‘recently restored’ (< 4 years) and ‘mature restored’ (> 10 years) sites. Data collected at 28 additional sites in the catchment informed us on distances to potential source populations. Habitat suitability describes the fit between environmental conditions (abiotic site data) and species preferences and was used to assess the role of environmental filtering. We evaluated the role of the biotic filter based on trait overlap, referring to possible interspecific competition. Communities collected at recently restored sites differed from those of mature restored and unimpacted sites. Taxa present at recently restored and mature sites had closer source populations than those of unimpacted sites. Taxa at mature and unimpacted sites had a better fit to the present habitats than those of recently restored sites. The trait overlap did not differ between co-occurring and not co-occurring taxa at any of the site groups. Our findings show that communities of mature restored sites that have been restored more than 10 years ago, resembled those of unimpacted sites. Dispersal was most important in early years of recovery. Taxa occurrences at sites with nearby source populations and low habitat suitability are likely the result of high rates of dispersal from upstream sources (mass effects). These can be caused by hatching events or environmental disturbances. Habitat suitability played a larger role for communities at mature and unimpacted sites which indicates that optimal communities shape over time. We did not find indications that competition played a role for community assembly. Hence, dispersal and habitat suitability were most relevant for species’ occurrences. Competition could be more important on micro scales and the results may differ if species abundances are taken into account. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes