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Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nature-based solutions (NBS) are increasingly suggested to address biodiversity decline and climate change. However, many ecosystems are hardly used as NBS, including ponds and pondscapes. We therefore examine how policies and practices affect their implementation as NBS. Using a content analysis of policy documents and stakeholder inputs, we assess the policy context in eight countries but also zoom in on policies and practices in seventeen pondscapes. We derive three key insights: first, a protective status for a pond or pondscape interlinks with other enabling factors for NBS implementation, and protection and conservation should therefore be considered more often as NBS. Second, there is a shortage of, especially long-term, financing. Third, local leadership should be nurtured to overcome a lack of institutional cooperation and stakeholder awareness as well as fragmented land ownership. Beyond that, we show that implementation barriers interlink and interventions should therefore address several barriers simultaneously. [ABSTRACT FROM AUTHOR]

The estimation of biodiversity is complex in remote areas like Andean-Amazon piedmont where the lack of knowledge is noticeable and most species have not yet been identified. An alternative to the taxonomical approach to assess biodiversity and community structure is to study the body size structure of the community. The present study aimed to identify systematic changes of the size structure of fish communities along the altitudinal gradient of pristine Andean streams. At the same time, we assessed if size structure of fish communities could be an alternative or complementary approach to traditional taxonomic metrics of ecological assessment. This study was conducted along two rivers of eastern Andean piedmont: Hacha River and Alto Madre de Dios basin. Our analysis showed lower values of total size range, maximum length and number of size classes in the highest places and increasing in lower reaches of the rivers. Concerning abundance size spectra, we found flatter slopes (indicating higher relative abundance of large fish) and lower coefficient of determination (i.e. less linear size spectra) and intercept at y-axis on upstream reaches. On the other hand, fish abundance, species richness and species diversity increasing from upstream to downstream. These systematic changes on size-related variables were similar using both basins together or independently and may be used in future studies as management reference conditions when assessing the effect of perturbations in freshwater ecosystems, while bypassing the error associated with the lack of taxonomic information. [ABSTRACT FROM AUTHOR]

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]

The widespread salinisation of freshwater ecosystems poses a major threat to the biodiversity, functioning, and services that they provide. Human activities promote freshwater salinisation through multiple drivers (e.g., agriculture, resource extraction, urbanisation) that are amplified by climate change. Due to its complexity, we are still far from fully understanding the ecological and evolutionary consequences of freshwater salinisation. Here, we assess current research gaps and present a research agenda to guide future studies. We identified different gaps in taxonomic groups, levels of biological organisation, and geographic regions. We suggest focusing on global- and landscape-scale processes, functional approaches, genetic and molecular levels, and eco-evolutionary dynamics as key future avenues to predict the consequences of freshwater salinisation for ecosystems and human societies. The global acceleration of freshwater salinisation due to human activities such as agriculture, resource extraction, and urbanisation and its amplification by climate change is unequivocal. Although research in this field is growing, there are key aspects at the ecological and evolutionary levels that remain unaddressed. Increasing salinisation is a problem as it can increase the stress or mortality of freshwater organisms, leading to a loss of diversity and/or functionality of freshwater ecosystems but also the services and benefits to human societies that they provide. We identify the main gaps of recent research and suggest a research agenda to facilitate future research efforts in order to achieve a more comprehensive understanding on freshwater salinisation. [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]

Fish community feeding and production rates may differ between lakes despite similar fish biomass levels because of differences in size structure and local temperature. Therefore, across‐lake comparisons of the strength and direction of top‐down and bottom‐up fish–phytoplankton relationships should consider these factors. We used the metabolic theory of ecology to calculate size‐ and temperature‐corrected community energy demand (CEDom) and community production (CP) of omnivorous fishes in 227 European lakes from major habitat types (MHTs) of polar freshwaters, temperate floodplain rivers and wetlands, and temperate coastal rivers. We related CEDom with total phosphorus (TP)‐corrected chlorophyll a (Chl a) concentrations to evaluate a potential top‐down directed trophic cascade from fish to phytoplankton. Furthermore, we related Chl a with CP to demonstrate potential bottom‐up effects of phytoplankton on fish. For both analyses, we added the CED of piscivorous fishes (CEDpi) as a predictor to account for potential predation effects on the omnivorous fish community. CEDom was weakly positively related with TP‐corrected Chl a, but the strength of the relationship differed between MHTs. In contrast, CP was consistently positively related with Chl a in the entire dataset. CEDpi did not contribute to top‐down or bottom‐up relationships. The application of metabolic variables characterizing fish community feeding and production rates makes these results robust because the approach accounted for the usually neglected effects of fish size and temperature in across‐lake comparisons. Our results suggest that bottom‐up effects from phytoplankton on fish secondary production in lakes are substantially stronger than top‐down effects from fish on phytoplankton biomass. [ABSTRACT FROM AUTHOR]

Highlights • Small sized species of alien fish dominate the lower Ebro River fish community. • Normalized Abundance Spectra (NAS) of fish were evaluated monthly for one year. • NAS reflected hydro-peaking impacts on the fish community. • High hydro-peaking conditions may increase predatory efficiency of piscivorous fish. Abstract The European Water Framework Directive requires the integration of body size characters as an important part of fish-based bioassessment tools for freshwaters ecological status determination. The study of the entire fish community size-structure provides valuable information about food web capacity, food web stability and ecological efficiency of aquatic ecosystems. One of the most used representations of community size structure is the Normalized Abundance Spectra (NAS) that provides an approximation of the total fish abundance and food web capacity (through the parameter y-intercept) and an estimation of food web efficiency (through the slope of the linear regression). In this study we explored NAS of the lower Ebro River fish community by integrating data from monthly electrofishing samplings during a whole year (November 2014- October 2015). We found that the percentage of total alien and alien-prey individuals were directly related with y-intercept and inversely related with slope of NAS. This is because the bulk of the community consists of introduced species of small body length. Furthermore, we detected significant relationships between NAS-related parameters and the hydrological variables describing diel flow oscillations and daily flow variability. Based on this, we suggest that high flow variability conditions and, above all, high hydro-peaking conditions, caused a diminution of the total abundance of fish and a decrease of the proportion of small sized fish (i.e. lower y-intercept and flatter slopes of NAS, respectively). Finally, a significant interaction between hydro-peaking and the percentage of alien-predators suggests that high hydro-peaking conditions benefit predation by facilitating predator-prey encounters. This is reflected by strong linear relationship between NAS parameters and percentage of piscivorous at high hydropeaking conditions that disappears at low hydro-peaking fluctuations. We concluded that the high proportion of alien fishes and the presence of a hydropower generation plant that operates by hydro-peaking are important factors determining fish size structure in the lower Ebro River. [ABSTRACT FROM AUTHOR]

Fish can alter food web structure through trophic cascades. While most studies conducted in oligotrophic subarctic lakes show strong top-down control on consumers in the presence of fish, several studies undertaken in eutrophic subarctic Lake Mývatn, Iceland, suggest that it is consumer-resource interactions that drive the whole-lake community. Here, we used stable isotopes of carbon and nitrogen from the main food web compartments derived from a 3-month in situ-controlled mesocosm experiment involving two treatments (with and without fish) with three replicates each to determine the effects of fish on the trophic structure of the Lake Mývatn food web. We found that the whole food web trophic structure shifted towards the upper part of the water column (more planktonic habitat) in fishless enclosures. Additionally, the trophic niche of organisms occupying the base of the food web became more diversified when fish were absent, and the trophic redundancy of all taxa decreased (more dissimilar trophic niches). Stronger top-down effects may also result from global warming, producing increased abundance of planktivorous fish in subarctic lakes. Our results indicate that this could lead to a shift in trophic niche and reduced trophic diversity of most food web organisms. [ABSTRACT FROM AUTHOR]

Abstract: The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density‐size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi‐trophic communities is exactly −1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator‐prey mass ratio (PPMR) is fixed at 104. Here we provide evidence from four multi‐trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than −1.0 (range −1.14 to −1.19, with 95% CIs excluding −1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass‐size data pairs from the four systems (−1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (−1.18) assuming a constant PPMR of 104. Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass‐size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat‐specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE‐estimates. [ABSTRACT FROM AUTHOR]

The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment to elucidate how periphyton (on inert substrata), epiphyton and epipelon biomass responded to a nitrogen (N) pulse, an approximately tenfold enrichment of the NO-pool, under three contrasting warming scenarios: ambient temperature and ca. +3°C and ca. +4.5°C elevated temperatures (hereafter T1, T2 and T3). After the N pulse, we found a higher periphyton biomass at elevated than at ambient temperatures but no change in epiphyton biomass. Epipelon biomass was lower in T3 than in T1. Both periphyton and epiphyton biomasses correlated negatively with snail biomass, while epiphyton biomass correlated positively with light. Different responses to higher temperatures under short-term extreme nutrient loading conditions may be attributed to differences in the access to nutrient sources and light. Our data suggest that the biomass of periphyton in oligotrophic clear-water lakes will increase significantly under conditions exhibiting short-term extreme nutrient loading in a warmer climate. [ABSTRACT FROM AUTHOR]

The rivers and streams of the world are becoming saltier due to human activities. In spite of the potential damage that salt pollution can cause on freshwater ecosystems, this is an issue that is currently poorly managed. Here we explored intraspecific differences in the sensitivity of freshwater fauna to two major ions (Cl − and SO 4 2 − ) using the net-spinning caddisfly Hydropsyche exocellata Dufour 1841 (Trichoptera, Hydropsychidae) as a model organism. We exposed H. exocellata to saline solutions (reaching a conductivity of 2.5 mS cm − 1 ) with Cl − :SO 4 2 − ratios similar to those occurring in effluents coming from the meat, mining and paper industries, which release dissolved salts to rivers and streams in Spain. We used two different populations, coming from low and high conductivity streams. To assess toxicity, we measured sub-lethal endpoints: locomotion, symmetry of the food-capturing nets and oxidative stress biomarkers. According to biomarkers and net building, the population historically exposed to lower conductivities (B10) showed higher levels of stress than the population historically exposed to higher conductivities (L102). However, the differences between populations were not strong. For example, net symmetry was lower in the B10 than in the L102 only 48 h after treatment was applied, and biomarkers showed a variety of responses, with no discernable pattern. Also, treatment effects were rather weak, i.e. only some endpoints, and in most cases only in the B10 population, showed a significant response to treatment. The lack of consistent differences between populations and treatments could be related to the high salt tolerance of H. exocellata , since both populations were collected from streams with relatively high conductivities. The sub-lethal effects tested in this study can offer an interesting and promising tool to monitor freshwater salinization by combining physiological and behavioural bioindicators. [ABSTRACT FROM AUTHOR]

In spite of being a widespread activity causing the salinization of rivers worldwide, the impact of potash mining on river ecosystems is poorly understood. Here we used a mesocosm approach to test the effects of a salt effluent coming from a potash mine on algal and aquatic invertebrate communities at different concentrations and release modes (i.e. press versus pulse releases). Algal biomass was higher in salt treatments than in control (i.e. river water), with an increase in salt-tolerant diatom species. Salt addition had an effect on invertebrate community composition that was mainly related with changes in the abundance of certain taxa. Short (i.e. 48 h long) salt pulses had no significant effect on the algal and invertebrate communities. The biotic indices showed a weak response to treatment, with only the treatment with the highest salt concentration causing a consistent (i.e. according to all indices) reduction in the ecological quality of the streams and only by the end of the study. Overall, the treatment's effects were time-dependent, being more clear by the end of the study. Our results suggest that potash mining has the potential to significantly alter biological communities of surrounding rivers and streams, and that specific biotic indices to detect salt pollution should be developed., (Copyright © 2016 Elsevier Ltd. All rights reserved.)