Christian Schürings

Freshwater and terrestrial ecosystems are linked by reciprocal flows of energy and nutrients, including the emergence of aquatic insects that provide abundant, high-quality prey for riparian birds. Local studies show that emergent aquatic insects can enhance bird reproduction and survival, yet it remains unclear whether such associations scale up across landscapes and persist under human disturbance. Here we show that the richness of mayflies, stoneflies and caddisflies (Ephemeroptera, Plecoptera and Trichoptera; EPT), an indicator of freshwater integrity and insect emergence, predicts the prevalence of 288 bird species across 14,177 rivers in the contiguous USA, even after accounting for human land use. Aerial insectivorous birds exhibit more than threefold higher prevalence at sites with high compared with low EPT richness. This linkage is consistent across river types describing hydrology (including intermittent systems), temperature and geomorphology, with the strongest gains occurring in rivers with low baseline bird prevalence. The associations are weaker in urbanized sites but persist in highly agricultural landscapes provided that EPT richness remains relatively high. Our findings provide continental-scale evidence that emergent aquatic insects sustain riparian birds, underscoring that freshwater conservation offers considerable co-benefits to terrestrial ecosystems.

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°C), cool (11°C–15°C) and warm (> 15°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.

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.

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.

Background: 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. Results: Changes in abiotic stressors emerged as the most consistent drivers of ecological status, explaining substantial variation (R ² = 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 (R ² = 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. Conclusion: 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.

In response to the global freshwater biodiversity crisis this study examines the drivers, influencing recovery and degradation in riverine benthic macroinvertebrate communities across Germany. Utilizing the Asymmetric Response Concept (ARC), which posits that species tolerances to stressors, dispersal capacity, and biotic interactions are critical drivers in aquatic ecosystem recovery, we analyzed a comprehensive dataset from 1568 sites, sampled between 2004 and 2022. Our findings indicate that abiotic stress consistently influences ecological status in both recovery and degradation phases. Interspecific competition shows a stronger positive relationship with ecological status improvements during recovery phases than during degradation, underscoring its importance in the recovery process. Additionally, land use intensity has a nuanced impact: catchments with higher proportions of cropland and urban areas are more likely to recover, while forested catchments are more prone to degradation. This study supports the ARC and highlights the complex interplay of biotic and abiotic variables in shaping ecological outcomes, underscoring the importance of integrated management approaches in freshwater conservation and restoration efforts.