Biogeochemical indicators (waters/diatoms) of acid mine drainage pollution in the Odiel river (Iberian Pyritic Belt, SW Spain).

Odiel river basin is located in the Iberian Pyritic Belt (IPB) and mostly of its tributaries are severely affected by acid mine drainage (AMD). It is originated when pyritic minerals from abandoned mines, especially mineral residues from waste rock dams, get in contact with air and water. Fifteen sampling points were chosen to analyze interactions between diatom communities and water hydrogeochemistry. Considering physicochemical characteristics, sampling points were assigned as highly, moderately, and unpolluted by AMD. No correlation was observed between ecological diversity indexes and physico-chemical parameters. However, a dependency relationship between diatom species distribution and specific pH, conductivity, redox potential, sulfate, and metal concentrations was observed. Cluster analysis based on Pearson correlation and rs values of the non-parametric Spearman correlation allowed to identify Pinnularia acidophila, Pinnularia subcapitata var. elongata, and Eunotia exigua as the main bioindicators of AMD-polluted Odiel streams. Finally, a principal component analysis led to associate the most abundant diatoms species to specific physico-chemical parameters.