Does river restoration increase ecosystem services?

Rivers provide ecosystem services (ES) that benefit people, but worldwide, many rivers are severely degraded thus compromising service supply. River restoration aims at reversing this condition. We reviewed the scientific literature to synthesise published effects of restoration on ES and to identify which specific ES commonly benefit from or recede after river restoration. Most of the reviewed studies (n = 850) did not present insight into restoration effects on ES, but merely used ES terminology (n = 762; 89.6%), indicating that researchers often implicitly assume an increase of ES following restoration. Only a small fraction of studies reported qualitative (n = 53; 6.2%) or quantitative effects on ES (n = 35; 4.1%). From those 88 core studies, we found evidence for an increase of 12 ES. We observed little consistency in ES assessments, which impeded the comparability. Trade-offs between ES and decreasing ES after restoration were more frequently observed in models than in empirical studies. The studies also showed a strong bias toward the coverage of ecoregions and ecosystems. In the future, not only will further studies be needed to close the knowledge gap, but there is also a clear need to adapt existing legal frameworks which drive restoration, to define ES as a water management objective.