Ecological Status Should Be Considered When Evaluating and Mitigating the Effects of River Connectivity Losses in European Rivers

The deterioration of European freshwater ecosystems, driven by habitat fragmentation and connectivity loss, seriously threatens biodiversity and ecosystem integrity. While restoration efforts often focus on reconnecting river networks, ecological assessments tend to overlook the broader concept of connectivity. This study highlights the need to incorporate ecological quality into connectivity assessments, ensuring more effective restoration that is aligned with European Union (EU) conservation policies. Using the dendritic connectivity index for potamodromous (DCIp) species, we analysed seven connectivity scenarios, integrating natural and artificial barriers to assess both structural connectivity and quality-weighted connectivity. These scenarios included: (1) structural connectivity considering only natural barriers (S_NB) and (2) all barriers (S_AB); (3) quality-weighted connectivity considering natural barriers (W_NB), and (4) all barriers (W_AB); three enhanced scenarios considering all barriers with (5) improved quality (W_AB_IQ), (6) improved probability of connectivity (W_AB_IC), and (7) improved quality and probability of connectivity (W_AB_IQC). Connectivity values varied across scenarios, with the natural baseline (S_NB) showing the highest connectivity values (mean = 0.98). When the natural baseline was weighted by the GES probability (W_NB), connectivity values dropped considerably (mean = 0.30). Incorporating all barriers (W_AB) further reduced the connectivity values (mean = 0.26). The improved scenario W_AB_IQC showed notable connectivity improvements (mean = 0.40). This study underscores the importance of integrating ecological quality into river connectivity assessments. It demonstrates that restoring habitat quality alongside connectivity restoration can substantially enhance river ecosystems. Prioritising restoration in high-quality areas maximises ecological and social benefits, supports sustainable river management, improves connectivity, and promotes biodiversity conservation.