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Abstract

In order to identify the major sources of trace metals (TM) in the Portuguese coastal waters, 58 surface water samples were collected during September 1988. The area sampled extended from the Tagus Estuary (down to a salinity of 25) to cape Ste Marie on the southern coast of Portugal. Dissolved metal concentrations in the fully marine waters ranged from 30 to 250 pM for Cd, 0.7-15 nM for Cu, 0.9-20 nM for Zn and 1.8-4.5 nM for Ni. Within the Tagus Estuary (salinity 25), concentrations increased to 3400 pM for Cd, 26 nM for Cu, 14 nM for Ni and 230 nM for Zn.

The large-scale distribution of these metals is dominated by two strong continental sources, both probably linked to the exploitation of pyrite ores. In the Tagus Estuary, TM enrichments can be mostly attributed to a pyrite roasting plant located on the shore in front of Lisbon. Concerning the south Portuguese shelf waters, several hypotheses are proposed to explain their elevated metal concentrations. We particularly discussed the likely influence of the Titfto/Odiel Rivers located 100 km eastward, an influence well known in the shelf waters of the Gulf of Cadiz. These rivers are extremely metal-rich because of acid mine tailings originating from their catchments. Between these two regions, up-welling of relatively metal-poor water largely contributes to the dilution of the continental inputs. Indeed, water exchanges on the shelf linked to the up-welling involve water fluxes 500 times higher than the Tagus River flow, and renew the coastal waters that are thus cleaned from terrestrial contamination. Contrary to many other up-welling systems in non-contaminated areas, the Portuguese up-welling does not act as a source of trace-metal enrichment of the continental margin waters.

Additional information

Authors: COTTE-KRIEF M, Institut de Biogeochimie Marine, Ecole Normale Superieure, F-92120 Montrouge (FR);GUIEU C, Institut de Biogeochimie Marine, Ecole Normale Superieure, F-92120 Montrouge (FR);THOMAS A, Institut de Biogeochimie Marine, Ecole Normale Superieure, F-92120 Montrouge (FR);MARTIN J, Institut de Biogeochimie Marine, Ecole Normale Superieure, F-92120 Montrouge (FR)
Bibliographic Reference: Article: Marine Chemistry 71 (2000), pp. 199-214
Record Number: 200013041 / Last updated on: 2001-01-24
Category: PUBLICATION
Original language: en
Available languages: en