Abstract
A Lagrangian approach based on a physical–biogeochemical modeling was used to compare the potential transfer of cadmium (Cd) from natural and anthropogenic sources to plankton communities (Cd-uptake) in the North-West African upwelling. In this region, coastal upwelling was estimated to be the main natural source of Cd while the most significant anthropogenic source for marine ecosystem is provided by phosphate industry. In our model experiment, Cd-uptake (natural or anthropogenic) in the North-West African upwelling is the result of an interplay between the Cd dispersion (by advection processes) and the simulated biological productivity. In the Moroccan waters, advection processes limit the residence time of water masses resulting in a low natural Cd-uptake by plankton communities while anthropogenic Cd-uptake is high. As expected, the situation is reversed in the Senegalo-Mauritanian upwelling where natural Cd-uptake is higher than anthropogenic Cd-uptake. Based upon an estimate of Cd sources, our modeling study shows, unexpectedly, that the anthropogenic signal of potential Cd-bioaccumulation in the Moroccan upwelling is of the same order of magnitude as the natural signal mainly present in the Senegalo-Mauritanian upwelling region. A comparison with observed Cd levels in mollusk and fishes, which shows overall agreement with our simulations, is confirming our estimates.
Highlights
As much as 40% of the world's population lives within 100 km of the shoreline (Martínez et al, 2007) and this population continues to grow, increasing our reliance and impact on the coastal ocean
► We model the physical–biogeochemical dynamics in the North-West African upwelling. ► We model the transport of cadmium from natural and anthropogenic sources. ► We derive proxies of potential cadmium absorption and bioaccumulation in the plankton food chain. ► The anthropogenic signal off Morocco at least equals the natural upwelling signal off Mauritania. ► We compare our results with observed cadmium levels in mollusks and fishes
Maximum southward velocity is found in the coastal upwelling jet (CanUC) from Cape Cantin to Cape Blanc where upwelling occurs all year round
Summary
As much as 40% of the world's population lives within 100 km of the shoreline (Martínez et al, 2007) and this population continues to grow, increasing our reliance and impact on the coastal ocean. Phosphogypsum are particles containing significant abundance of crustal elements as heavy metals (the most toxic being mercury and cadmium; see list in Gaudry et al (2007)). The Moroccan phosphate industry releases large amounts of heavy metals, cadmium (Cd), in the North-West (NW) African upwelling around Safi and Jorf-Lasfar (33°N). These are responsible for a significant contamination of molluscs communities (Banaoui et al, 2004; Benbrahim et al, 2006; Chafik et al, 2001; Cheggour et al, 1999; Gaudry et al, 2007; Maanan, 2008, 2007). Phosphate industry is present though less developed in Mauritania and Senegal
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