Plant communities of extreme acidic waters: The Rio Tinto case

As one of the largest extreme acidic environments in the world the Río Tinto (Spain) constitutes a useful case to study the vegetation resistant to waters, sediments and soils with pH < 3 and high concentrations of S, Fe, Cu and other metals. In this territory two types of water courses coexist: the extreme acidic waters, with a low pH and high amounts of S and Fe, usually of a red color, and those that are not extremely acid, which include colorless acid, neutral and basic waters with much less S and Fe. An exhaustive study of the riparian vegetation present along the two first sections of the Río Tinto and in less extreme, neighboring water courses was carried out (61 inventories). Some water quality variables (pH, redox, Fe, Cu and O2) were measured in sampled points. Correspondence between plant community composition and water quality was analyzed through hierarchical classification, detrended correspondence analysis and canonical correspondence analysis.Results indicate clear differences in vegetation between extremely acidic and less extreme water courses. A total of 50 emergent plant species have been found in extremely acidic waters. Among them the most frequent were Erica andevalensis Cabezudo and J. Rivera, Scirpoides holoschoenus (L.) Soják and Nerium oleander L. Additionally, pH, redox, Fe and O2 concentrations were significantly related to the floristic data.

► We compare the riparian vegetation of the extremely acidic waters of the Río Tinto basin in Spain with less acidic control sites.
► We test the effect of pH, redox, Fe, Cu and O2 on the distribution of riparian plant species.
► Extreme acidic waters are impoverished in species but have their own endemic species and plant communities.
► Erica andevalensis, Scirpoides holoschoenus and Nerium oleander are the most frequent species along extreme acidic waters.
► pH, redox, Fe and O2 concentrations were significantly related to the floristic data.