Toxicity indices-based insights for sustainable sediment management in hydropower-regulated river systems

Sediments are key components of aquatic ecosystems, accumulating up to 99 % of potentially toxic elements (PTEs) in the hydrological cycle. However, they are vulnerable to anthropogenic impacts, particularly impoundments from hydropower plants. This study evaluates spatial and temporal changes in six heavy metals (Cu, Zn, Pb, Cd, Cr, Ni) and assesses sediment toxicity using six indices (Geochemical Method, LAWA, Pollution Index, Geoaccumulation Index, Contamination Factor, and Ecological Risk Index) at three hydropower plants on the Bóbr River in Poland (Ciechanowice, Jelenia Góra, Kraszewice). Results show that 94.4 % of the sites located downstream of hydropower plants exhibited reduced sediment toxicity. Statistically significant reductions in heavy metal concentrations were confirmed using the Kruskal-Wallis test, although levels remained higher than at reference sites. This pattern is linked to upstream sediment accumulation, where finer, more sorptive particles dominate. The extent of this effect varies by plant type and location. Most samples were classified as having very low to low toxicity (classes I-II), though occasional moderate to high toxicity (classes III-V) was detected, indicating possible remediation needs. These findings highlight the importance of informed sediment management and offer guidance for hydropower development in the broader context of climate, energy, and land degradation strategies.