PARENT SESSION
TP3 CICTA2001
3:00 PM to 6:30 PM, Tuesday, 08 May 2001
Session Chair: J.V. Tarazona
Room 3

(235) Metal biogeochemistry and fluxes in the Rio Tinto estuarine and coastal system, southwest Spain.

Braungardt, Charlotte¹, Achterberg, Eric¹, Nimmo, Malcolm¹, Elbaz-Poulichet, Francoise², Morley, Nickolas³, ^{1 2 3}

ABSTRACT- The Rio Tinto and Rio Odiel drain a metalliferous mining area in the Iberian Pyrite Belt, which is one of the world's most important sulphide mineralisations. The rivers receive acid mine drainage and as a result observed pH values were low (< 3) and dissolved metal concentrations were extremely high (e.g. 2.6 mM Zn, 860 M Cu, 6.0 M Cd and 4.1 M Pb). The seasonal cycle of low precipitation and flash floods was an important factor in causing more severe contamination of the rivers with Fe, Al, Mn, Zn, Cu, Ni, Co and Cd during the wet, compared to the dry seasons. Estuarine metal geochemistry of dissolved Fe, Mn, Zn, Cu, Ni,Co and Cd was primarily controlled by pH. This resulted in largely conservative mixing behaviour up to ca. pH = 5 (at salinity ca. 30), with the exception of the upper Tinto estuary, where these metals were mobilised from the sediment in the turbidity maximum zone. Voltammetric speciation studies showed that Cu complexing organic ligands in the estuary were saturated, and thermodynamic calculations indicated that the concentration of Cu²⁺, which is thought to be the metal's most toxic species, reached values (pCu²⁺ <9) that are toxic to some marine and estuarine organisms. Flux estimations indicated that the daily dissolved metal export from this system to the coastal zone averages 10 t Zn, 2.3 t Cu, 180 kg Ni and 240 kg Co. Therefore, the Tinto/Odiel system represents an important source of metals to European coastal waters. Ship-board on-line measurements of Zn, Cu and Ni in the Gulf of Cadiz revealed metal plumes associated with the Tinto/Odiel system and the Guadiana and Guadalquivir rivers. As a result of entrainment by the Atlantic Ocean surface current flowing into the Mediterranean Sea, the metal contamination in waters of the Gulf of Cadiz is transported south and eastward, and can be traced east of Gibraltar.

Key words: Rio Tinto, acid mine drainage, metal flux, metal speciation