title: Water acidification trends in a reservoir of the Iberian Pyrite Belt (SW Spain).
abstract: Scarcity of waters is the main limiting factor of economic development in most arid and semi-arid regions worldwide. The construction of reservoirs may be an optimal solution to assure water availability if the drainage area shows low disturbances. This is the quandary of mining areas where economic development relies on water accessibility. Water acidification trends were investigated in the Sancho Reservoir (SW Spain) in the last 20 years. The acidity (pH3-5) and high dissolved metal concentrations (e.g., 4.4 mg/L of Al, 2.1mg/L of Mn, 1.9 mg/L of Zn) observed in the Sancho, together with the large volume stored (between 37 and 55 Mm(3)), makes this reservoir an extreme case of surface water pollution worldwide. A progressive acidification has been observed since 2003, as evidenced by decreasing pH values and increasing dissolved metal concentrations, especially noticeable after 2007. The increase in the net acidity in the reservoir originates from the higher input of metals and acidity due to the rebound effect after the mining closure in 2001. This trend was not detected in the river feeding the reservoir due to its great hydrological and hydrochemical variability, typical of the Mediterranean climate. Chemical analysis and absolute dating of sediments identified a progressive enrichment in S and metals (i.e., Fe, Zn Cu, Ni, Co and Cd) in the upper 20 cm, which reinforce the year 2002/03 as the onset of the acidification of the reservoir. The decrease of pH values from 4-5 to 3-4 occurred later than the increase in sulfate and metals due to pH-buffering by Al. The acid mine drainage (AMD) pressure has caused an increment of dissolved Fe and other metals, as well as a change in the pH buffering role, exerted now by Fe. These processes were simulated by PHREEQC, which confirms that the acidification trend will continue, causing pH values to reach 2.5 if AMD pressure persists.
authors.affiliation: Department of Geology, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain. Electronic address: carlos.ruiz@dgeo.uhu.es.
authors.forename: C R
authors.initials: CR
authors.lastname: Cánovas
authors.affiliation: Department of Geodynamics and Paleontology, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Olías
authors.affiliation: Department of Geology, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Macias
authors.affiliation: Institute of Environment Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Torres
authors.affiliation: Department of Applied Physics, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain.
authors.forename: E G
authors.initials: EG
authors.lastname: San Miguel
authors.affiliation: Department of Geodynamics and Paleontology, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Galván
authors.affiliation: Institute of Environment Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Ayora
authors.affiliation: Department of Geology, Faculty of Experimental Sciences, University of Huelva, Campus el Carmen s/n, 21071 Huelva, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Nieto
keywords: Hydrological modeling; Rebound effect; Sediment dating; pH-buffering