Macroinvertebrate functional composition along a gradient of hydromorphological restoration effort in a lowland channelized river

Hydromorphological restoration efforts aim to enhance the ecological integrity of degraded river systems, yet their effectiveness in improving biodiversity and community composition remains context-dependent. This study examined macroinvertebrate responses to varying levels of restoration along the Eau Blanche river (Belgium), where restoration interventions reintroduced lotic characteristics to a channelized river. We assessed community structure, functional composition, and metrics related to habitat heterogeneity and water velocity across a gradient of restoration effort over a 10-yr period. We linked hydromorphological and biological data with co-inertia, between-class analysis and correlations. By focusing on a single river characterized by homogeneous typological alteration, this study minimizes between-sites and catchment-specific variabilities. Restoration actions increased habitat heterogeneity metrics, such as water depth and velocity, substrate diversity, and patch size. High current velocity and related variables emerged as primary factors explaining macroinvertebrate density, richness, and life history traits. Increased velocities reduced substrate clogging, favouring taxon richness while modifying life history traits, such as respiration modes and feeding strategies. Conversely, degraded sites exhibited traits consistent with depositional environments, including taxa adapted to low oxygen and fine sediments. Results align with literature indicating the importance of velocity and heterogeneity for invertebrate communities. They also suggest that restoration-induced typological shifts can act as ecological filters, reshaping traits composition, particularly in lowland rivers with high depositional dynamics.