Metals in river sediments from a semi-arid Mediterranean basin were investigated from upstream to downstream during contrasting hydrological conditions in 2014 and 2015. The level and origin of the contamination were evaluated using several geochemical and isotopic indicators. Elements were grouped by their level of contamination: high (Pb > Cd > Zn > Cu) and low (Al, Fe, Cr, Co, Ni). Multiple local sources of contamination were identified (industrial, agricultural and domestic waste), as well as very specific ones (gasoline station) and diffuse pollution from atmospheric deposition (gasoline, ores, aerosols). During storm events, the upstream dams can either be secondary sources of contamination or dilutors through particles derived from natural erosion. The contamination was slowed downstream due to the river geomorphology, but eventually washed into the Mediterranean Sea by intense storm events. Naturally derived elements (Co, Ni, Cr, As) were associated with Al, Fe and Mn oxides or clays, and anthropogenic originated metals with phosphorus (Cd and Zn), sulphur (Cu) and POC (Pb enrichment). Cadmium and Pb were the most available metals upstream and at the outlet, but their availability was not strictly related to their degree of contamination. These conclusions could be drawn thanks to an approach by multiple indicators.
Keywords: Available fraction; Dam; Geochemical and isotopic indices; Hydrology; River sediments; Trace metals.
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