Physical-chemical characteristics of the superficial waters affected by acid mine drainage in the southern sector of the Guadiana basin (South-western of the Iberian Peninsula)

The southern sector of the Guadiana basin drains the central-western part of the Iberian Pyrite Belt (FPI), an area with many polymetallic sulphide deposits and residues of the mining activity, generating an acidic leach with large quantities of sulphates, metals and metalloids in solution. These acidic leacheates are incorporated into the river network causing the contamination of the superficial water of the basin. The object of this study is to identify the sources of contamination by acid mine drainage (AMD) in this sector, and to identify the seasonal variations. In this work, the results of the physical-chemical parameters are exposed (tª, C.E, pH, Eh and O.D) together with the chemical analysis of the water from 79 points of observation. The data show a strong seasonal variation with a deterioration of the water quality in the dry season. It is also possible to observe a natural attenuation of the pollution with increasing distance from the pollution source (mining areas), and an important dilution of the contaminants in the estuary as a result of the mixing with marine water, increase of the pH, and the loss of the metals in solutio