Development of a holistic approach for river health assessment: from bioindicators to the ecosystem.

Freshwater ecosystems are crucial for biodiversity conservation, pollution mitigation and climate regulation. However, anthropogenic pressures, including agricultural and industrial activities and urbanisation, degrade water quality and ecological status. This study assessed the health of the Elsa River, a tributary of the Arno in Tuscany (Italy), through an integrated and holistic methodology combining chemical, ecological and ecotoxicological parameters. Water quality (nitrate, phosphate, ammonium concentrations and pH) was assessed through a citizen science project. This initiative actively involved local communities and high schools, fostering the sharing of local knowledge to identify sampling sites and address territorial challenges. Ecological status was assessed using the Extended Biotic Index (EBI) and Fluvial Functionality Index (FFI). Italian chubs (Squalius squalus) were employed as bioindicators to investigate microplastic ingestion, contaminant levels (heavy metals, organochlorines) and a battery of biomarkers for evaluating genotoxic, neurotoxic effects, oxidative stress, metabolic stress and the presence of polycyclic aromatic hydrocarbon (PAH) metabolites. The results showed a progressive decline in water quality and ecological status from upstream to downstream, particularly after the urbanised area and the river park, where microplastic ingestion in fish peaked at 2.5 items/individual. A genotoxic effect was highlighted, significantly correlated with the presence of mercury, polychlorinated biphenyls and benzo(a)pyrene's metabolites. This holistic approach, integrating physico-chemical analysis, ecological assessments and ecotoxicological effects on biota, provided a comprehensive understanding of the river's health. It enabled the identification of contaminants and hypothesised their sources, like illegal urban waste disposal, vehicular traffic and polluted tributaries.