A comparative ecological study of two acidic rivers in Southwestern Spain

We have analyzed select physicochemical and biological characteristics of two acidic rivers, the Tinto and the Odiel, located in the Pyritic Belt of Southwestern Spain. Despite a common geography and geochemistry, they exhibit important differences. Most of the measured physicochemical parameters, especially pH and those related to conductivity (heavy metal concentrations), showed more extreme values in the Tinto than in the Odiel. However, it was at the microbiological level (fungal and bacterial populations) where both rivers showed the most important differences according to the statistical analysis of principal components. Lithoautotrophic bacteria were more abundant in the more acidic Tinto River and fungal diversity varied significantly from one river to the other.