Supplementary file 1_Adapting soil fertility indices to evaluate sediment quality in rivers used for hydropower generation.docx

River sediments play a key ecological role but are increasingly altered by hydropower development, causing their accumulation and changing properties. This study evaluated the fertility of sediments in the Bóbr River (southwestern Poland), an intensively dammed system with 71 hydropower plants Sediments were collected upstream and downstream of three HPs (Ciechanowice, Jelenia Góra, Kraszewice) and at natural reference points during spring and autumn 2022–2023. 19 physicochemical parameters were analyzed into 5 fertility indices: Soil Fertility Index Soil Evaluation Factor Soil Nutrient Index (NIV), Synthetic Soil Fertility Index and Soil Quality Index All indices consistently showed higher fertility in sediments upstream of HPs, intermediate fertility downstream, and lowest fertility at reference sites. This pattern reflects the accumulation of fine-grained, nutrient- and metal-enriched material upstream dams, while coarser, nutrient-poor sands dominate downstream. Statistical analyses (Mann–Whitney U test, Principal component analysis, Cliff’s delta) confirmed significant spatial differences in fertility-related parameters and medium to strong hydropower impacts on sediment properties. The study demonstrates that hydropower-induced sedimentation enhances localized fertility but also concentrates potentially toxic metals, complicating sediment reuse as agricultural material. These findings highlight the dual ecological and management implications of sediment trapping and the need for integrated assessment frameworks that link fertility and contamination risks. The research fills a critical gap by adapting soil fertility indices to riverine sediments, providing a novel methodological approach to evaluate sediment quality in hydropower-regulated rivers and support sustainable sediment management under, e.g., the EU Water Framework Directive and UN Sustainable Development Goals.