Fuzzy Modeling of the Spatial Evolution of the Chemistry in the Tinto River (SW Spain)

The oxidation of sulfide minerals generates acid waters containing high concentrations of sulfates, metals and metalloids. The overriding chemical mechanism of AMD has now been reasonably well understood, although accurate assessment or prediction of its ecological impact are still difficult due to the complexity of the processes involved. The main objective of this work is to characterize the behavior of As conditioned by the presence of other elements which are characteristic of AMD pollution, both in the generating milieu, and in the receiving milieu of the Tinto river, and thus to be able to establish the differences in behavior at both sites by using a fuzzy computer tool. The extremely low As values are due to different circumstances at each sampling site: the pH in generating milieu may reach extremely high values while in receiving milieu it does not rise above medium–high values. The differences remain for extremely high As values, proving very much conditioned by the temperature in the generating milieu and only compatible with extremely high values for this, while in the receiving milieu it has barely any influence. It is the redox potential especially that presents a more pronounced difference, while in generating milieu it can have any value except extremely high and low, in receiving milieu we only find extremely low and very concentrated values.