Copper, zinc and lead impact in SW Iberian shelf sediments: An assessment of recent historical changes in Guadiana river basin

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In the present study, lithogenic/biogenic and anthropogenic elements were determined in five sediment cores collected at the SW Iberian Continental Shelf in order to investigate the spatial and temporal heavy metal distribution and to associate them with specific continental influences/events. Elemental concentrations suggest a heavy metal (Cu, Zn and Pb) enrichment at the upper sections of all the cores. This enrichment is larger for cores localised closer to the coastline and probably exposed to a stronger continental influence. The geochemical regional background values for the studied elements are reached at ∼25-30 cm for all the studied cores with one exception (core 8), which showed to be metal-enriched down to ∼80 cm. It is worthnoting that core 8 is located closer to the coastal area, in a different fine sedimentary deposit, in which the deposition rates seem to be considerably higher. Enrichment factors (EF) calculated by using the natural background value determined at the deeper layers show that the EF values vary at the upper sections of cores, between 1.0 and 4.5 and the spatial distribution of the sediment cores show a similar behaviour in the heavy metal distribution patterns along this area of the continental shelf. Cu, Zn and Pb are heavy metals associated with mining exploitation along the Iberian Pyrite Belt, one of the most important mining areas of southwestern Europe, with massive orebodies of these metals. The combination of enrichment factors downcore profiles with sedimentation rate values signifies the beginning of heavy metal pollution in shelf sediments (∼200-250 years ago) and is coincident with the mining exploitation reactivation during the XIX century.

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