Effects of restoration on macrophyte and macroinvertebrate ecological status and biodiversity in lowland streams in Denmark

Abstract Introduction Habitat restoration is applied to promote ecological recovery in degraded freshwater systems. However, it remains unclear whether stream restoration measures enhance Water Framework Directive (WFD) ecological status and biodiversity. Objectives We assessed whether two widely implemented restoration measures in lowland streams—channel re‐meandering and gravel augmentation—(1) improve ecological status assessed using WFD‐calibrated indices and (2) restore biodiversity across alpha, beta, and gamma diversities, as well as abundance of rare and/or declining species, toward least‐disturbed reference conditions. Methods Using a space‐for‐time approach, we compared macrophyte and macroinvertebrate community composition in restored stream reaches with near‐natural and degraded stream reaches within the same region. Results Restoration revealed contrasting outcomes among biological groups and diversity metrics. Ecological status improved for macroinvertebrates, but remained low for macrophytes, with restored below reference conditions. Paradoxically, gamma diversity was highest in degraded and lowest in restored reaches for all species groups. Macroinvertebrate alpha diversity peaked in reference reaches, and Ephemeroptera , Plecoptera , and Trichoptera (EPT) taxa showed comparable alpha diversity between reference and restored reaches, whereas macrophyte alpha diversity did not differ among stream types. Gamma and beta diversities, along with rare and/or declining species, were consistently lowest in restored relative to non‐restored reaches, indicating biotic homogenization rather than biodiversity recovery. Conclusions Re‐meandering and gravel augmentation can achieve WFD compliance for macroinvertebrates but fail to improve macrophyte‐based ecological status and reduce regional biodiversity. Uniform restoration homogenizes biological communities, failing to support rare and/or declining species or restoring compositional characteristics of least‐disturbed conditions.