When natural disturbances and anthropogenic stressors interact, non‐perennial reaches become particularly vulnerable to global change: Insights from France

Context . Worldwide, more than 50% of river reaches experience flow intermittence and this proportion is increasing due to climate change and water abstraction, with foreseeable impacts on ecosystem function and structure. Concomitantly, multiple anthropogenic impacts associated with land‐use changes are impairing river ecosystems. Evaluating whether and how anthropogenic impacts and flow intermittence interact is paramount to guide ecosystem management in a rapidly changing world. Goal . First, we aimed at testing whether and how the effects of intermittence and anthropogenic stressors on biodiversity interact and secondly to evaluate whether such interactions change depending on the biomonitoring metric employed. Methods . We used a large dataset of French river biomonitoring networks ( n = 545 sites) in which macroinvertebrates were sampled along wide gradients of flow intermittence and multiple anthropogenic stressors. We ran generalized linear models to test the independent and interactive effects of flow intermittence and anthropogenic stressors on both traditional and functional‐based biomonitoring metrics. Main results . We found that most metrics responded interactively to the effects of flow intermittence and anthropogenic stressors, except functional redundancy, which responded only to anthropogenic impacts, showing a single effect. In addition, we observed that both taxonomic and functional diversity metrics of macroinvertebrates are particularly vulnerable to anthropogenic stressors in non‐perennial reaches compared with perennial ones. Synthesis and applications . Our results show that functional redundancy provides a consistent indicator of anthropogenic impact across both perennial and non‐perennial rivers. We suggest that incorporating this metric into biomonitoring frameworks could improve the detection of ecological degradation in increasingly intermittent river networks, offering a more robust basis for management and conservation decisions under global change.