Relationships between hydrogeochemistry and diatoms in acid mine drainage affected media: The case of Iberian pyrite belt; functioning models for an all metallogenetic province

The Iberian Pyritic Belt (IPB) is one of the most important metallogenic provinces, which hosts massive sulfides and extends over 230 km from Canal Caveira-Lousal in Portugal to Gerena (near Seville) in Spain. It has 88 active and inactive mines only in the Spanish part and near 30 in Portugal that generate Acid Mine Drainage (AMD) pollution to the main river basins, Corona, Roxo (Portugal), Odiel, Tinto, Guadiamar (Spain) and Chanza-Guadiana (Portugal/Spain) and consequenty to the 35 acidic sampling sites, 14 in Portugal and 21 in Spain, selected for this unique study. The physico-chemical parameters of waters (EC, Eh, pH, Al, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, SO₄²⁻), acidic diatoms (%Pinacid) and diatom diversity (N°sps) were determined in the laboratory. Then, the results were integrated in a database with 16 variables and 35 sampling points to be statistically analyzed by factor and cluster analysis. In the first, for the 35 sampling sites, it showed a clear inexistence of ecological barriers, exposing how could distantly sampling points be paired together. The last, allowed the pollution–biota interaction models formulation governed by 2 factors: 1-Unrestored Mining Surfaces and 2-WFD (Water Framework Directive) exceeding limits. Dispersion diagram showed that although the unrestored mining surface increases, starting from a certain concentration of contaminants, salts begin to precipitate: the AMD process increases but the WFD does not. There are numerous works in the scientific literature aimed to define diatom-hydro-geo-chemistry interrelationships, but none that covers an entire metallogenetic province where ecological barriers could exist, conditioning the diatom species and groups evolution and distribution in an acidic (pH: 1.90–4.43) environment.