Assessing groundwater-river interactions for sustainable water management in the mine-contaminated Mediterranean Bravona catchment (Corsica, France)

Study region The Bravona River watershed (Corsica, France), a Mediterranean coastal catchment affected by legacy arsenic mining pollution. Study focus Mediterranean coastal catchments affected by legacy mining pollution face increasing pressure from climate change and water demand, requiring improved understanding of groundwater–river interactions controlling contaminant dynamics. This study investigates the role of the downstream alluvial aquifer in arsenic dynamics within the Bravona watershed, using a seasonal multi-tracer approach combining hydrochemistry, stable water isotopes (δ¹⁸O, δ²H), radiogenic tracers (³H, ²²²Rn), and arsenic concentrations over a complete hydrological cycle (2022–2023). New hydrological insights for the region Results reveal strong seasonal variability in groundwater–river interactions, with alluvial groundwater contributing between 16% and 43% of downstream river flow. Tritium and radon data indicate longer residence times in the alluvial aquifer and enhanced groundwater support during low-flow periods. Arsenic concentrations in the downstream river are decoupled from upstream mine inputs and primarily controlled by seasonal hydrological connectivity. During low-flow conditions, increased groundwater contribution attenuates arsenic concentrations in the downstream Bravona River, whereas high-flow periods favor upstream-dominated signals. The alluvial aquifer remains weakly contaminated (As < 10 µg/L) and acts as a hydrological buffer rather than a secondary contamination source. These findings demonstrate that seasonal groundwater–river connectivity governs arsenic dynamics and highlight the value of integrated multi-tracer approaches for water management in mining-impacted Mediterranean catchments.