Pollution dynamics in Mediterranean micro-estuarine hydrosystems in Corsica, France, under seasonally variable tourism pressure: Integrating isotope hydrology, geochemical tracers, and organic contaminants of emerging concern

Study region Four small Mediterranean coastal watersheds and their associated micro-estuaries in north-western Corsica (France). Study focus Investigating the combined influence of seasonally variable tourism pressures and hydrological dynamics on contamination processes in Mediterranean micro-estuarine systems. Two sampling campaigns were conducted during pre-tourism and post-tourism periods to capture seasonal variability in anthropogenic pressures and their interactions with flow conditions. A multi-tracer approach integrating major geochemical elements, stable isotopes, and contaminants of emerging concern (CECs) was applied to characterize contaminant sources, transport, and attenuation processes. New hydrological insights for the region Geochemical and isotopic signatures indicate a close interdependence between flow regimes and local geochemical conditions controlling contaminant occurrence and mobility. In perennial systems, rainfall events enhance dilution, resulting in lower contaminant concentrations despite increased tourism pressure. In temporary systems limited attenuation capacity is observed during post-tourism periods, leading to elevated concentrations of labile compounds, notably caffeine and paraxanthine, indicating direct infiltration of untreated wastewater from campsites. Similar patterns are observed in adjacent alluvial aquifers, where increased CEC levels during post-tourism periods reflect limited attenuation potential. Episodic surface-groundwater connectivity facilitates contaminant transfer. In micro-estuaries, high-flow events promote seawater mixing, inducing salinity-driven desorption of sediment-bound contaminants and transforming these environments into temporary active pollution sources. These findings provide a robust framework for understanding contamination dynamics in vulnerable Mediterranean micro-estuarine systems subject to severe tourism and climatic pressures.