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Numerous riverine ecosystems in Iran are currently suffering due to various human activities, which are directly affecting the physico-chemical conditions of running waters and influencing the aquatic biota. In this study, we chose the cold-water streams of the Southern Caspian Sea Basin in Iran to analyse human pressures and develop a multi-metric fish index for the cold-water streams dominated by brown trout, Salmo trutta in this Basin. To do this, the fish and environmental data were sampled in 67 medium sized streams in the Caspian Mountains. In total, nine fish metrics were calculated. Moreover, 27 criteria describing major anthropogenic pressures for the entire sampling area were used to generate a regional pressure index that accounted for potential effects of multiple human pressures. For the index development, we first defined reference sites and then quantified differences of fish metrics between the reference and impacted sites. The multiple linear regressions were used for describing metric responses to natural environmental differences in the absence of any human pressures. Finally, by testing the ability of each metric for discrimination of impacted and reference sites as well as their sensitivity to a gradient of regional pressure index, the metrics density of brown trout and biomass of sub-adult brown trout explained human pressures best. Our multi-metric fish index performed well in discriminating between reference and impacted sites, giving a significant negative linear response to a gradient of regional pressure index. In general, the development of such an index offers an opportunity to enhance national bio-monitoring programmes in Iran.

Embargo until February 26, 2023 Despite advances in conceptual understanding, single-stressor abatement approaches remain common in the management of fresh waters, even though they can produce unexpected ecological responses when multiple stressors interact. Here we identify limitations restricting the development of multiple-stressor management strategies and address these, bridging theory and practice, within a novel empirical framework. Those critical limitations include that (i) monitoring schemes fall short of accounting for theory on relationships between multiple-stressor interactions and ecological responses, (ii) current empirical modelling approaches neglect the prevalence and intensity of multiple-stressor interactions, and (iii) mechanisms of stressor interactions are often poorly understood. We offer practical recommendations for the use of empirical models and experiments to predict the effects of freshwater degradation in response to changes in multiple stressors, demonstrating this approach in a case study. Drawing on our framework, we offer practical recommendations to support the development of effective management strategies in three general multiple-stressor scenarios.

Plans are currently being drafted for the next decade of action on biodiversity—both the post‐2020 Global Biodiversity Framework of the Convention on Biological Diversity (CBD) and Biodiversity Strategy of the European Union (EU). Freshwater biodiversity is disproportionately threatened and underprioritized relative to the marine and terrestrial biota, despite supporting a richness of species and ecosystems with their own intrinsic value and providing multiple essential ecosystem services. Future policies and strategies must have a greater focus on the unique ecology of freshwater life and its multiple threats, and now is a critical time to reflect on how this may be achieved. We identify priority topics including environmental flows, water quality, invasive species, integrated water resources management, strategic conservation planning, and emerging technologies for freshwater ecosystem monitoring. We synthesize these topics with decades of first‐hand experience and recent literature into 14 special recommendations for global freshwater biodiversity conservation based on the successes and setbacks of European policy, management, and research. Applying and following these recommendations will inform and enhance the ability of global and European post‐2020 biodiversity agreements to halt and reverse the rapid global decline of freshwater biodiversity. We thank the organizers of the ALTER‐Net/EKLIPSE Post‐2020 Biodiversity Workshop for discussions that led to this collaboration. CBvR was supported by a Fulbright Early Career Scholar Award from the Fulbright Spain Commission, SJT by the NERC Highlight Topic “Hydroscape” (NE/N006437/1), SCJ and GK by the “GLANCE” project (01LN1320A) from the German Federal Ministry of Education and Research (BMBF), HPG by the BMBF “BIBS” project (01LC1501G1), KAW by the Rural & Environment Science & Analytical Services Division of the Scottish Government (2016–2021 Strategic Research programme), SD by the Leibniz Competition (J45/2018), AIL by FCT (CESAM; UID/AMB/50017/2019), IJ by the J. E. Purkyně Fellowship of the Czech Academy of Science, and VH by a Ramon y Cajal Contract (RYC‐2013‐13979).

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors. For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response vari- able. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions. This work was supported by the MARS project (Managing Aquatic Ecosystems and Water Resources under Multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), contract no. 603378 (http://www.mars-project.eu). Further support was received through the ILES (SAW- 2015-IGB-1) and BIBS (BMBF 01LC1501G) projects. Partner organizations provided 25% cofunding through their institutional budgets. We thank J. Strackbein, J. Lorenz and L. Mack for their support. This work was supported by the MARS project (Managing Aquatic Ecosystems and Water Resources under Multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), contract no. 603378 (http://www.mars-project.eu). Further support was received through the ILES (SAW- 2015-IGB-1) and BIBS (BMBF 01LC1501G) projects. Partner organizations provided 25% cofunding through their institutional budgets. We thank J. Strackbein, J. Lorenz and L. Mack for their support.

This chapter deals with human stressors affecting aquatic ecosystems in Europe. Section 8.1 briefly reviews the historical evolution of human stressors and related drivers (particularly land use pressures), notably the decrease in agricultural area, occurring simultaneously with the intensification of agriculture and urbanization, where physical and chemical degradation are extreme. Section 8.2 describes stressors and regions in which such stressors predominate. Urbanization is a major pressure in the Central Baltic region, where both inadequately treated urban sewage and wastewater from heavy industries are numerous and severe. Particularly in the Mediterranean Region, barriers and dams of all sizes are widespread and altered or reduced flows are major stressors throughout. The percentage of riparian areas in good condition is only about 25%. Along the Atlantic Coast, poorly treated aquaculture pollutants are common. Section 8.3 shows how stressors usually act simultaneously, with various possibilities of interactions. A moderate to bad ecological status predominates in water bodies with more than three stressors. Finally, in Section 8.4 , we describe the goals and planning of the Water Framework Directive (WFD) versus the present situation. Approximately one-third of European waters surveyed reach a good to high ecological status, but there has been little improvement in the last years. Riverine water bodies and transitional waters generally have more stressors and biological impacts, and thus poorer ecological status than lakes, reservoirs, and coastal waters. Central–Baltic rivers generally reveal the worst ecological statuses in Europe, whereas the Baltic Sea and Greater North Sea regions have the worst coastal and transitional waters. Regions with intensive agriculture and high population density are affected by multiple pollutants and have poor ecological statuses, whereas better ecological statuses are reported for floodplains with the remnants of natural areas. Urbanization, floodplain infrastructures, and nutrient pollution (especially nitrogen) are the most important predictors of ecological degradation. The next generations of river basin management plans (RBMP, due in 2021–27) face a huge challenge in reaching the WFD goal of good ecological statuses in all water bodies.

This work addresses multiple human stressors and their impacts on fish assemblages of the Drava and Mura rivers in southern Austria. The impacts of single and multiple human stressors on riverine fish assemblages in these basins were disentangled, based on an extensive dataset. Stressor configuration, i.e. various metrics of multiple stressors belonging to stressor groups hydrology, morphology, connectivity and water quality were investigated for the first time at river basin scale in Austria. As biological response variables, the Fish Index Austria (FIA) and its related single as well as the WFD biological- and total state were investigated. Stressor-response analysis shows divergent results, but a general trend of decreasing ecological integrity with increasing number of stressors and maximum stressor is observed. Fish metrics based on age structure, fish region index and biological status responded best to single stressors and/or their combinations. The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi-stressor restoration- and management.

A major issue for water resource management is the assessment of environmental degradation of lotic ecosystems. The overall aim of this study is to develop a multi-metric fish index for the cyprinid streams of the Caspian Sea Basin (MMICS) in Iran. As species diversity and composition as well as population structure in the studied streams are different to other regions, there is a substantial need to develop a new fish index. We sampled fish and environmental data of 102 sites in medium sized streams. We analysed human pressures at different spatial scales and determined applicable fish metrics showing a response to human pressures. In total, five structural and functional types of metrics (i.e. biodiversity, habitat, reproduction, trophic level and water quality sensitivity) were considered. In addition, we used 29 criteria describing major anthropogenic human pressures at sampling sites and generated a regional pressure index (RPI) that accounted for potential effects of multiple human pressures.For the MMICS development, we first defined reference sites (least disturbed) and secondly quantified differences of fish metrics between reference and impaired sites. We used a Generalised Linear Model (GLM) to describe metric responses to natural environmental differences in least disturbed conditions. By including impaired sites, the residual distributions of these models described the response range of each metric to human pressures, independently of natural environmental influence.Finally, seven fish metrics showed the best ability to discriminate between impaired and reference sites. The multi-metric fish index performed well in discriminating human pressure classes, giving a significant negative linear response to a gradient of the RPI. These methods can be used for further development of a standardised monitoring tool to assess the ecological status and trends in biological condition for streams of the whole country, considering its complex and diverse geology and climate.

Europaische Fliesgewasser stehen unter starkem Nutzungsdruck. Dabei zahlen Eingriffe in die Hydromorphologie im Rahmen energiewirtschaftlicher Nutzung oder durch Hochwasserschutzmasnahmen zu den starksten Belastungen. Heute gibt es nur noch wenige verbleibende naturliche oder naturnahe Gewasserstrecken. In Osterreich befinden sich derzeit nur 15 % der Wasserkorper in einem „sehr guten“ und 22 % in einem „guten“ okologischen Zustand. Um die Ziele der EU-Wasserrahmenrichtlinie zu erreichen, sind im Nationalen Gewasserbewirtschaftungsplan Masnahmen definiert, mittels derer der gute Zustand der Wasserkorper erreicht werden soll bzw. kunftige Beeintrachtigungen und Verschlechterungen des Zustandes verhindert werden sollen. Gleichzeitig gilt es, die Ziele der EU-Erneuerbare-Energien-Richtlinie zu erreichen. In Osterreich spielt dabei insbesondere der weitere Ausbau der Wasserkraft eine wesentliche Rolle. Um sowohl Schutz- als auch Nutzungsziele zu erreichen bzw. um eine transparente Abwagung unterschiedlicher Interessen zu gewahrleisten, ist eine strategische Planung notwendig. Im hier vorlegenden Artikel werden diesbezugliche Empfehlungen, Leitlinien und ausgewahlte methodische Ansatze zusammengefasst. Anhand von drei methodisch aufeinander aufbauenden Fallbeispielen wird auserdem detailliert vorgestellt, wie Schutzpriorisierungen von Gewasserstrecken als Pre-planning-Instrumente herangezogen werden konnen. Auserdem wird eine Methodik vorgestellt, die bei bereits bestehenden Kraftwerksplanungen auf (uber-)regionaler Ebene durch die Integration gewasserokologischer, naturschutzfachlicher und energiewirtschaftlicher Aspekte einen wesentlichen Beitrag bei der Entscheidungsfindung leisten kann.

This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions.

Hydropower (HP) is an important renewable energy source contributing 65.7% to Austria’s national electricity generation. However, HP is also associated with ecosystem degradations jeopardizing the aims of the EU Water Framework Directive (WFD) and Habitats Directive. Based on the EU Renewable Energy Directive (RED), the Austrian Energy Strategy has defined goals to further increase HP production by 3.5 TWh until 2015. Because national strategies for HP development are widely missing, hydropower plants (HPPs) are planned and approved on a local and regional level, often neglecting the overall optimum for energy supply and ecology. Therefore, a decision support tool (Hy:Con) was developed to integrate the energy-economic characteristics of planned HPPs and conservation needs of ecologically sensible river stretches. Based on 102 planned HPPs in Austria, Hy:Con identified HPPs with high economic attractiveness and low conservation concerns. The results show that owing to the already high HP exploitation in Austria, only a minor number of projects are without conservation conflicts. Upgrading of existing HPPs was associated with least ecological impacts, while HPPs with reservoirs are favoured over run-of-river plants. Cumulated ecological effects of numerous small HPPs are significant, whereas their contribution to overall energy production is comparatively small. Hy:Con represents a strategic instrument that can help decision makers to govern the implementation of the RED and WFD in a transparent way to pinpoint the limitations of future HP development and to avoid conflicts and stranded investments. © 2015 The Authors. River Research and Applications Published by John Wiley & Sons Ltd

Running water ecosystems of Europe are affected by various human pressures. However, little is known about the prevalence, spatial patterns, interactions with natural environment and co-occurrence of pressures. This study represents the first high-resolution data analysis of human pressures at the European scale, where important pressure criteria for 9330 sampling sites in 14 European countries were analysed. We identified 15 criteria describing major anthropogenic degradation and combined these into a global pressure index by taking additive effects of multiple pressures into account. Rivers are affected by alterations of water quality (59%), hydrology (41%) and morphology (38%). Connectivity is disrupted at the catchment level in 85% and 35% at the river segment level. Approximately 31% of all sites are affected by one, 29% by two, 28% by three and 12% by four pressure groups; only 21% are unaffected. In total, 47% of the sites are multi-impacted. Approximately 90% of lowland rivers are impacted by a combination of all four pressure groups.

Laut Nationalem Gewasserbewirtschaftungsplan verfehlen 63 % der osterreichischen Fliesgewasser das in der EU-Wasserrahmenrichtlinie definierte Umweltziel, was zum Grosteil auf Beeintrachtigung der Gewasserstrukturen sowie der Abfluss- und Kontinuumsverhaltnisse zuruckzufuhren ist. Die Wasserkraft zahlt mit den Eingriffen "Stau", "Restwasser" und "Schwall" neben dem Hochwasserschutz zu den masgeblichen Belastungsfaktoren. Die Energiestrategie Osterreich sieht einen Ausbau der Wasserkraft um 3,5 TWh/a vor. Anhand des Belastungsfaktors "Stau" und vergleichender Ausbauszenarien wird im Rahmen vorliegender Arbeit aufgezeigt, dass Speicher-, Lauf- und Kleinkraftwerke sehr unterschiedliche Belastungen fur Fliesgewasserokosysteme mit sich bringen. Da das Potenzial an naturbelassenen Flusslandschaften in Osterreich schon sehr limitiert ist, sollten nur jene Varianten bzw. Erhohungen des Ausbaugrads weiter verfolgt werden, die lediglich zu geringfugigen okologischen Beeintrachtigungen fuhren.

The catchment land-use composition of 249 fish sampling sites in Austrian running waters revealed effects on the biological integrity. Beyond correlative analysis, we investigated (1) which land-use category had the strongest effect on fish, (2) whether metrics of functional fish guilds reacted differently, (3) whether there were cumulative effects of land-use categories, and (4) whether effects varied in strength across river types. We fed 5 land-use categories into regression trees to predict the European Fish Index or fish metric of intolerant species (mainly Salmo trutta fario). Agriculture and urbanisation were the best predictors and indicated significant effects at levels of >23.3 and >2%, respectively. Model performance was R2 = 0.15 with the Fish Index and R2 = 0.46 with intolerant species. The tree structure showed a cumulative effect from agriculture and urbanisation. For the intolerant species metric, a combination of high percentages for agriculture and urbanisation was related to moderate status, whereas