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Aim: The maintenance of broad‐scale connectivity patterns is suggested as a sustainable strategy for biodiversity preservation. However, explicit approaches for quantifying the functional role of different areas in biogeographic connectivity have been elusive. Freshwaters are spatially structured ecosystems critically endangered because of human activities and global change, demanding connectivity‐based approaches for their conservation. Mass effects—the increase in local diversity by immigration—and corridor effects—the connections with distant communities—are basic and relevant mechanisms connecting diversity with landscape configuration. Here, we identified freshwater hotspots areas for mass and corridor effects across Europe. Location: Europe. Methods: Using satellite images, we quantified the areas of ephemeral, temporal and permanent freshwaters. The landscape structure of the freshwater ecoregions was represented as a directed‐graph, and the link weights were determined by the distance between cells and the water cover. Three centrality metrics were used to rank freshwater areas with respect to their potential role in dispersal‐mediated mechanisms. Out‐degree represents the potential of an area to operate as a diversity source to other regions. In‐degree reflects the importance that incoming dispersal may have in local diversity. Betweenness refers to the importance of local areas for connecting other distant areas. Results: We detected great concentrations of source hotspots on the northern regions associated to lentic ecosystems, main European rivers acting as ecological corridors for all freshwaters, and a mixed distribution of connectivity hotspots in southern and Mediterranean ecoregions, associated with lentic and/or lotic systems. Main Conclusions: We showed an explicit connection between landscape structure and dispersal process at large geographic scales, highlighting hotspots of connectivity for the European waterscape. The spatial distribution of hotspots points to differences in landscape configurations potentially accounting for biogeographic diversity patterns and for mechanisms that have to be considered in conservation planning. [ABSTRACT FROM AUTHOR]

Much information is available on community composition and abundance of submerged macrophytes in North temperate lakes, including their response to variation in environmental variables. Less is known about macrophytes in other climate regions. We studied 98 shallow lakes distributed in three different European latitudinal regions. The lakes were selected along mutually independent gradients of macrophyte coverage and total phosphorus and were sampled monthly from May to October for water chemistry and physical variables. We tested for changes in the impact of selected environmental variables on the macrophyte assemblage, coverage and richness in the three regions. Coverage was measured along transects during July/August and June in the northern/central and southern European lakes, respectively. Correspondence Discriminant Analysis was used to detect for differences in macrophyte composition among different regions, and univariate regression trees were used to detect relationships between environmental variables and macrophyte coverage and richness. In the northern lakes, the coverage was mainly related to chlorophyll a followed by pH, and richness was related to Secchi depth and chlorophyll a. In the southern lakes, pH was the key environmental variable for both coverage and richness. North-south differences may be of relevance for determining management strategies related to global climate change. [ABSTRACT FROM AUTHOR]

Aim Our aim was to document geographical patterns of variation in the body-size structure of European lake fish assemblages along abiotic gradients, and any differences in fish assemblage structure. We hypothesized that patterns in the body-size structure of entire lake fish assemblages are primarily temperature driven and consistent with the dominant pattern of the temperature-size rule, which suggests a decrease in adult body size with increasing developmental temperature for many ectothermic species. Location 356 European lakes. Methods Variation in the body-size structure of fish assemblages was explored on a continental scale along gradients of temperature, morphometry, productivity and fish assemblage structure for 356 European lakes. The mean fish assemblage body-size and individual body-size distributions were selected as size metrics. Separate analyses were conducted for lakes located within five ecoregion subsets (Borealic Uplands/Tundra, FennoScandian Shield, Central Plains, Western Plains and Western Highlands) and for lakes with different functional fish classifications (cold-, cool- and warmwater fish assemblages). Results Geographical patterns of variation in the body-size structure of European lake fish assemblages could be clearly discerned along a temperature gradient for both the continental dataset (356 lakes) and the smaller geographical (ecoregion) subsets. We found systematic changes in fish assemblage body-size structure across temperature gradients in correspondence with the dominant thermal fish guild. The majority of the lakes, mainly located in the warmer European lowlands, were dominated by eurythermic cool- and warmwater fish assemblages, with smaller sized individuals characterized by linear individual body-size distributions. Lakes located in colder regions and dominated by stenothermic coldwater salmonids with larger sized individuals were characterized by unimodal or bimodal size distributions. The mean body size of cold-, cool- and warmwater fish assemblages changed uniformly along the temperature gradient. Main conclusions Patterns of variation in the body-size structure of European lake fish assemblages are consistent with the temperature-size rule. Temperature modifies fish assemblage size structure uniformly within the thermal fish guilds and in different ecoregions. Furthermore, our results indicate an increasing predictive power of temperature to explain variability in body-size structure when moving from warmer to colder geographical regions. [ABSTRACT FROM AUTHOR]

The implementation of the Water Framework Directive requires EU member states to establish and harmonize ecological status class boundaries for biological quality elements. In this paper, we describe an approach for defining ecological class boundaries that delineates shifts in lake ecosystem functioning and, therefore, provides ecologically meaningful targets for water policy in Europe., We collected an extensive data set of 810 lake-years from nine Central European countries, and we used phytoplankton chlorophyll a, a metric widely used to measure the impact of eutrophication in lakes. Our approach establishes chlorophyll a target values in relation to three significant ecological effects of eutrophication: the decline of aquatic macrophytes, the dominance of potentially harmful cyanobacteria and the major functional switch from a clear water to a turbid state., Ranges of threshold chlorophyll a concentrations are given for the two most common lake types in lowland Central Europe: for moderately deep lakes (mean depth 3-15 m), the greatest ecological shifts occur in the range 10-12 μg L−1 chlorophyll a, and for shallow lakes (<3 m mean depth), in the range 21-23 μg L−1 chlorophyll a., Synthesis and applications. Our study provides class boundaries for determining the ecological status of lakes, which have robust ecological consequences for lake functioning and which, therefore, provide strong and objective targets for sustainable water management in Europe. The results have been endorsed by all participant member states and adopted in the European Commission legislation, marking the first attempt in international water policy to move from physico-chemical quality standards to harmonized ecologically based quality targets. [ABSTRACT FROM AUTHOR]

We aimed to distinguish the relative contributions of natural and anthropogenic local factors on patterns of fish diversity in European lakes at different geographical scales., We compiled data from standardised fish monitoring using multimesh benthic gill nets, information on lake morphometry and on geographical, climatic and anthropogenic pressure variables from 1632 lakes in 11 European countries. By means of regression trees, we determined those natural and anthropogenic factors and their thresholds that best predicted local fish diversity, density and mean size. Generalised linear models were used to assess the influence of anthropogenic factors at smaller geographical and morphometric scales., Local fish species richness and diversity were related mainly to morphometric and (bio)geographical/climatic variables. Larger and deeper lakes in warm areas tended to be the most species rich and diverse. Fish density was related mainly to anthropogenically driven productivity but also was sensitive to geographical/climatic factors. Thus, warmer and shallower lower-altitude European lakes, which are usually more eutrophic, had higher fish densities than cold and deeper higher-altitude lakes. Fish size increased with altitude and declined with increasing seasonality and temperature., After controlling for the natural factors, productivity had a positive effect on fish species richness and diversity, whereas it negatively influenced fish size., Our results suggest that macroecological patterns of lake fish diversity across Europe are best predicted by natural factors. The contribution of anthropogenic factors to fish diversity was evident only via the effect of eutrophication at smaller geographical scales, whereas no effect could be found from hydromorphological pressures. From an applied perspective, these results suggest that bioassessment and biodiversity evaluation might be most effectively conducted and interpreted locally, where anthropogenic effects on biodiversity become more apparent. At a macroecological scale, the strong effect of environmental temperature on most components of fish diversity suggests future changes in fish diversity as a consequence of climate change. [ABSTRACT FROM AUTHOR]

Unlocking the full potential of ponds (small water bodies) and pondscapes (network of ponds) as Nature-based Solutions (NbS) is critical pursuit for enhancing ecosystems and societal resilience to climate change and other societal challenges. Despite scattered initiatives for pond/pondscape creation, restoration and management—each considered here a distinct NbS—there is a significant knowledge gap in utilising ponds/pondscapes as effective NbS. We aimed to assess these NbS in terms of their objectives, outcomes, effectiveness, multifunctionality, delivery of potentially conflicting effects, and the implementation process while considering their Nature's Contributions to People (NCPs, i.e., benefits to society). We compiled data on 183 NbS actions implemented across 93 ponds/pondscapes from 24 countries, predominantly from Europe, via a questionnaire distributed to experienced stakeholders implementing NbS in ponds/pondscapes. One single pond/pondscape may imply more than one NbS action. Two-thirds were in rural areas, and one-third in urban settings. Our analysis revealed that Creation of habitat for biodiversity was a primary delivery objective (targeted NCP) in the implementation of most NbS in ponds/pondscapes, often also combined with other NCPs such as Learning and inspiration , Regulation of water quantity , and Physical and psychological experiences , showcasing their intended multifunctionality. Implemented NbS primarily focused on climate change adaptation (especially Regulation of hazards and extreme events , and water quantity) rather than mitigation, with less emphasis on measures like direct greenhouse gas emissions reduction or enhancing carbon sinks. The costs associated with pond's NbS varied significantly depending on factors such as project scope, objectives, location, socio-economic-cultural system, and specific implementation requirements. The creation of ponds/pondscapes often entailed the highest financial investment, much more than their restoration or their management. In conclusion, our study underscores the multifunctionality of ponds/pondscapes and provides insights about their significant potential as cost-effective NbS for enhancing ecosystem and societal resilience to climate change and biodiversity. It underscores the importance of further research to fully understand and measure the diverse range of NbS they offer, particularly in the context of climate change mitigation. Standardised measurements of the NCP provided by these NbS in ponds/pondscapes are essential for validating managers' claims and exploring their role in addressing climate change. Cascading Benefits of Natural-Based Solutions (NbS) in Ponds and Pondscapes: Ponds and pondscapes serve as multifunctional NbS, delivering multiple Nature's Contributions to People (NCPs) to address climate-related challenges and Sustainable Development Goals (SDGs). They regulate the water quantity, mitigating flood risks, and ensuring water availability during droughts. Furthermore, these NbS indirectly support climate change adaptation by preserving microclimates, buffering temperature fluctuations, and providing vital habitats for diverse species, enhancing ecosystem resilience. Simultaneously, these actions offer recreational, cultural, educational, and well-being benefits to local communities impacted by climate change. Despite their potential, the capacity of ponds and pondscapes for climate change mitigation through carbon sequestration and storage remains unknown, requiring further exploration. [Display omitted] • Global study of 183 Nature-based Solutions in ponds/pondscapes in 24 countries. • Pondscapes' Nature-based Solutions are multifunctional and prioritise biodiversity. • Emphasis on climate change adaptation rather than mitigation. • Ponds/pondscapes offer cost-effective Nature-based Solutions. • Need for standardised measures to validate claims and explore climate mitigation. [ABSTRACT FROM AUTHOR]

Abstract: According to the Water Framework Directive (WFD), the status of European surface waters is assessed using aquatic organism groups. Here we present an overview of 297 assessment methods, based on a questionnaire survey addressing authorities in all countries implementing the WFD. Twenty-eight countries reported on methods applied to rivers (30%), coastal waters (26%), lakes (25%) and transitional waters (19%). More than half of the methods are based on macroscopic plants (28%) or benthic invertebrates (26%); in addition, phytoplankton (21%), fish (15%) and phytobenthos (10%) were assessed. Countries of Central and Western Europe had developed almost all methods required for the WFD implementation. Two main sampling strategies were discernable: small-scale sampling of the taxonomically diverse groups of benthic invertebrates and phytobenthos that demand elaborate processing, versus large-scale sampling of vast, species-poor plant stands or the mobile fish fauna. About three-quarters of methods identified organisms to species-level while in particular phytoplankton-based methods used class- or phylum-level, or included no taxonomic information. Out of nine metric types distinguished, river methods used more sensitivity and trait metrics while for other water categories abundance metrics prevailed. Fish-based methods showed the highest number of metrics. Fifty-six percent of methods focussed on the detection of eutrophication and organic pollution, with shares decreasing from autotrophic to heterotrophic organism groups: phytoplankton>phytobenthos>macroscopic plants>benthic invertebrates>fish fauna. The order was almost reverse for hydrological or morphological deterioration: fish fauna and macroscopic plants>benthic invertebrates>phytoplankton>phytobenthos. These pressures were mainly assessed by methods applied to rivers and transitional waters. The pressure-impact relationship of about one-third of methods was not tested empirically with methods for transitional waters being the least validated. The strength of relationships differed significantly between organism groups and water categories. The correlation coefficients generally covered a broad range (<0.4 to >0.8), but on average with the pattern: phytoplankton>macroscopic plants>benthic invertebrates>phytobenthos and fish fauna. In terms of water categories the following order resulted: coastal waters>lakes>transitional waters>rivers. Status boundaries were mostly defined using statistical approaches. We advocate better reflection of the necessary sampling effort and precision, full validations of pressure-impact relationships and an implementation of more ecological components into classification. [Copyright &y& Elsevier]