The contaminant load transported by the river Odiel to the Gulf of Cádiz (SW Spain)

Abstract

The river Odiel drains the central part of the Iberian Pyrite Belt, one of the oldest and most important sulphide mining districts of the world. Mining activities in the Odiel watershed started in the third millennium BC, and have continued until now with minor interruptions. As a consequence of this long mining history, large amounts of sulphides and sulphide-rich residues have been exposed in the surface. The oxidation of these sulphides has produced acidic effluents very rich in sulphate, metals and metalloids that end in the river Odiel. As a result, the water in the lower part of the river has a pH lower than 3.5. The amount of water transported by the river Odiel has important oscillations during the year. In order to understand the transport of pollutants in this river, we have combined a systematic sampling of the river several times during the year with the analysis of water flux and metal concentration data from the river Odiel for the last 20 years. With this long-term database, the calculated mean contaminant load transported by the river Odiel to the Huelva estuary and Gulf of Cádiz is 820.4 t/day of sulphate and 44.9 t/day of metals (Fe+Zn+Mn+Cu+Pb+Cd).