Satellite-based analysis of maritime traffic effects on water quality indicators in the Mediterranean basin

This study investigates the impact of maritime traffic intensity on water quality indicators in the Mediterranean Sea during the post-pandemic period (2022–2024). We examined the relationships between the monthly vessel route density from EMODnet and satellite-derived indicators, including chlorophyll-a (Chl-a), suspended particulate matter (SPM), absorption by gelbstoff and detrital material (ADG), NO₂ and SO₂ (Sentinel-5P), as well as in-situ heavy-metal concentrations. Pearson correlations were computed across pixel, EEZ-IHO regional and basin-wide scales, and annual growth rates were estimated for traffic and environmental variables. To assess whether water-quality responses differ across traffic-intensity levels, we applied the Kruskal‒Wallis test. The results show a strong positive temporal correlation between traffic intensity and NO₂ (r = 0.83, p < 0.001), whereas Chl-a (r = −0.86, p < 0.001), SPM and SO₂ display predominantly negative relationships. Passengers and fishing vessels exert the strongest effects, whereas cargo and tanker show weaker links. The Kruskal‒Wallis test confirms that Chl-a and ADG distributions differ significantly across low-, medium-, and high-traffic areas. Among the heavy metals, Pb displays the most consistent positive spatial correlations. AGR analysis shows that declining traffic along major corridors coincides with reduced NO₂, whereas growth in the Adriatic corresponds to increased Chl-a and SPM.