Background
Over the past few centuries, human impacts on river ecosystems have resulted in significant physical and ecological degradation of aquatic ecosystems. While the implementation of restoration measures has led to morphological improvements in rivers, positive biological responses, especially for benthic macroinvertebrates, are often limited. Alongside morphological degradation, recovery of invertebrate diversity is constrained by other factors acting at larger spatial scales, such as chemical pollution. Yet the extent to which chemical pollution limits the recovery of aquatic communities in restored river sections remains poorly studied. The application of current water quality monitoring methods may lead to inaccurate predictions of the effects of such stressors on river ecosystems. Therefore, effect-based methods (EBMs) are proposed as a complementary screening tool for the integrative assessment of river status.
Results
In this study, we provided a comprehensive assessment of the effects of local restoration measures by integrating ecological metrics, ecotoxicological tools, and chemical analyses. Although restoration measures were found to have a positive effect on habitat quality, no recovery of good ecological status in restored sections was found. The main pressure acting as a limiting factor for the improvement of benthic macroinvertebrate communities was found to be the prevailing chemical pollution. The effect of restoration age on benthic invertebrate communities and, for the first time, on ecotoxicological effects in response to hydromorphological river restoration showed no effect on ecological metrics or toxicity parameters.
Conclusion
In summary, the success of restoration needs to be assessed using a more integrative and multi-dimensional approach to identify limiting factors and to differentiate cases where restoration measures have not yet had time to take effect from cases where additional interventions may be required. The present results underscore the necessity for restoration initiatives to address not only individual stressors, such as morphological degradation, but also to incorporate comprehensive ecotoxicological monitoring to identify and mitigate any adverse effects that may compromise their effectiveness.