El impacto de la minería en los ríos Tinto y Odiel a lo largo de la historia

Abstract

The Tinto and Odiel Rivers represent an extreme case of acid mine drainage, with very high concentrations of toxic elements in the water. These rivers flow through materials of the Iberian Pyrite Belt (IPB) with abundant pollymetalic massive sulphide deposits, which have been exploited since antiquity. However, it is not clear, for the scientific community and society in general, if the current state presented is due to natural conditions, caused by the abundance of sulfur and low buffering capacity of the materials of the IPB, or the intense mining activity in the region. This paper aims to integrate prior information (geological, archaeological and historical) and provide a comprehensive view of how the conditions in these rivers have changed throughout history. In light of the results obtained five stages with different levels of toxic elements can be distinguished: 1) Phase of natural oxidation of sulfides (which began more than 24 millions years ago) at a geological scale, very slowly, so that there was not a noticeable impact on the basin, 2) The beginning of mining in the Chalcolithic period (III Millennium B.C.) and its continuation in the Bronze Age and Tartessian civilization, which caused a slight elevation of geochemical background levels, 3) The period of Roman mining, of great intensity for this period, which was a major impact on the watercourses of the area and in the Ria de Huelva estuary, 4) A decrease of pollution levels during the Middle and Modern Age and 5) A great impact since the mid-nineteenth century to the present, which caused an unprecedented degradation of these rivers, led to the demise of the rich fishing activities in the estuary of Huelva and even its effects reach the Gulf of Cadiz. In summary, the current state of the Tinto and Odiel Rivers is nothing natural and is mainly due to the intense mining activity during the last 150 years.