Mercury in the tinto-odiel estuarine system (Gulf of Cadiz, Spain): Sources and dispersion

The Tinto and Odiel are small rivers draining one of the largest sulphide deposits in the world. As a result of these deposits and a large industrial complex, the adjacent marine area receives a high amount of metal input. Mercury distribution in the Tinto-Odiel estuary, the Huelva Ria and the Gulf of Cadiz was assessed in water and suspended particulate matter (SPM) and sediments. In the rivers and estuaries, dissolved (HgD) and particulate (HgP) mercury showed wide variations (13 to 200 pM and 0.3 to 330 nmol g(-1) respectively) depending on the presence or not of sulphidic waters, phosphogypsum deposits, detrital pyrite and oxyhydroxides. In the Ria, concentrations were lower than 10 pM and 4.5 nmol g(-1) for HgD and HgP respectively. In surface waters of the Gulf of Cadiz, the average HgD concentration (pm standard deviation) was 2.9 pm 0.9 pM, which is similar to that of North Atlantic Central Waters. The surface sediments collected in the rivers, the Ria and the Gulf showed systematically enriched mercury compared to pre-industrial levels. Vertical mercury profiles in dated sediment cores were typical of anthropogenically influenced environments starting in the early Roman age. These distribution features suggest that most of the Hg discharged by the Huelva Ria is trapped in the sediments of the Gulf of Cadiz.