Temporal patterns of the wet deposition of Zn, Cu, Ni, Cd and Pb:: The Arcachon Lagoon (France)

We report here the first data set on wet deposition of heavy metals in the southwestern French coastal zone. In this region, there are two major sensitive coastal ecosystems: the Gironde Estuary and the Arcachon Lagoon. Chemical analyses of heavy metals were carried out by ICP-MS. Annual mean concentrations of the dissolved fraction in precipitation were 0.2, 3.4, 4.3, 8.1 and 30 mu g L-1 for Cd, Ni, Cu, Pb and Zn, respectively. In terms of annual fluxes, these numbers are of the same order of magnitude as the fluxes measured in southeastern France, but are higher than those measured in western Brittany. When extrapolated to the entire Bay of Biscay, the annual wet dissolved fluxes of Cd, Ni, Cu, Pb and Zn are respectively 7, 110, 140 340 and 1440 t yr(-1). According to available data in the literature, the regional Cd, Cu, Pb and Zn atmospheric fluxes for the Bay of Biscay are of the same order of magnitude as riverine inputs (Loire and Gironde). On a daily or weekly time scale, we observed a strong variability of elemental fluxes: up to 20% of the annual dissolved flux may occur in a rain event shorter than 3.5 days. Although elements display generally parallel variations with time, they sometimes follow independent behaviours (e.g. Pb and Cd), suggesting that they may derive from different geographical and/or pollution sources.