Tinto Versus Odiel: Two A.M.D. Polluted Rivers and an Unresolved Issue. An Artificial Intelligence Approach

The Iberian Pyrite Belt (SW Spain) is a highly relevant source of Acid Mine Drainage contamination on a global scale. Although the Tinto and Odiel Rivers, which cross the Iberian Pyrite Belt, have been widely studied by various authors, an issue is still pending: the study of the metal load distribution undergone by each of these rivers and, hence, the establishment of cause-effect relationships between the transported load in the final sections of both rivers, upstream of the tidal influence limits, and the characteristics of the input in each of the basins. To solve this, a water sampling campaign was conducted on both rivers on a daily basis from mid September 2007 to the end of May 2008, where pH, conductivity, redox potential, As, Cd, Fe, Cu, Zn, Mn and sulfate were analyzed. The results were treated with the PreFurGe tool, which is based on Fuzzy Logic. This showed that the order of abundance for the parameters analyzed for the Odiel River is SO<Subscript>4</Subscript>>Zn>Mn>Fe>Cu>Cd>As, whereas for the Tinto River it is SO<Subscript>4</Subscript>>Fe>Cu>Zn>Mn>Cd>As. This last pattern coincides with the order of abundance of elements in Pyrite. In the Tinto River, the metal with the highest rate is Fe, which presents mean values of 361.1 mg/L, whereas in the Odiel River iron mean concentration is 5.34 mg/L. This difference is due to higher precipitation of oxyhydroxysulfates of iron in the Odiel River as a result of the higher intensity of neutralization processes. Copyright Springer Science+Business Media B.V. 2011