Global budget assessment of natural and anthropogenic particulate copper fluxes to the Gulf of Lions

Drainage basin of the Gulf of Lions is largely dominated by vineyards which require the extensive use of Cu fungicides, leading to continuous copper accumulation in surface soils. In this area, soils depict among the highest Cu pollution levels in Europe. In order to draw up a global budget of Cu fluxes to the Gulf of Lions, our approach is based on long-term monitoring of Cu levels in riverine suspended sediments of the Rhone river and coastal Mediterranean river, as well as atmospheric deposits. These compartments have the particularity to be strongly influenced by extreme events typical of the region such as floods and Saharan dust episodes. In coastal rivers, Cu originates mainly from anthropogenic activities linked to viticulture while in the Rhone, calculated enrichment factors show weak anthropogenic influences. Atmospheric deposition often shows high Cu concentration and is both influenced by natural and anthropogenic sources. A main objective was also to decipher the Cu fluxes into their natural and anthropogenic components. A prerequisite was to determine natural backgrounds in the different compartments which surprisingly converge to similar values representative of both local geological nature of rocks in and the Saharan dust signature. Our study suggests that the Rhone River accounts on average for about 88% of both SPM fluxes and natural Cu fluxes to the Gulf of Lions. The contribution of the atmosphere and coastal rivers increases however to about 47% for anthropogenic Cu fluxes. They act as strong sources of contamination during more than a half of the year, from spring to fall, as they dominate the transfer of anthropogenic Cu to the sea. This represents a more continuous exposure for ecosystems whereas natural copper is generally delivered in the form of short pulses in relation to flood events and Saharan dust deposition during autumn and winter.