Los ríos que drenan la Faja Pirítica Ibérica (FPI) presentan un grave problema
de contaminación por aguas ácidas procedentes de minas de sulfuros abandonadas. La
construcción de la presa de Alcolea, localizada en el río Odiel, se empezó en 2014 pero
se paralizó en 2017, aunque actualmente hay una fuerte presión de los regantes para que
se retome. Debido a la acidez que presenta el río Odiel existe una gran polémica sobre
la calidad del agua de este embalse. En este trabajo se investiga la calidad del agua en
los grandes embalses de la FPI a partir de la información analítica de la red oficial de control de calidad. Los embalses no afectados por aguas ácidas (Jarrama y Corumbel)
tienen valores de pH próximos a neutros y muy baja concentración de sulfatos (<12 mg/L).
Los embalses de Andévalo y Olivargas tienen un nivel de afección intermedio, presentan
también un pH neutro aunque se tienen concentraciones más elevadas de sulfatos (~60
mg/L) y de algunos metales. El embalse del Sancho presenta un nivel de afección mucho
mayor y, como consecuencia, tiene un pH medio de 3,6 y elevadas concentraciones de
sulfatos (media de 184 mg/L) y metales tóxicos. Se estima que, si no se adoptan medidas de
restauración, las condiciones en el embalse de Alcolea serán similares o peores a las del
embalse del Sancho.
The rivers of the Iberian Pyrite Belt (IPB) have a very serious problem of
contamination by acid waters from abandoned sulphide mines, intensely exploited in the
past. The most extreme and well-known case is the Tinto river, but this problem affects
a much greater length of fluvial courses in the Odiel river basin. Other rivers in the IPB
that also receive acid leachates, although with less intensity, are the Rivera del Chanza
and the Guadiamar. In 2014, the Alcolea dam began to be built on the Odiel River, mainly
for agricultural use. This construction was stopped in 2017 but currently there is a strong
pressure from the irrigators to resume it. Due to the conditions of the Odiel River in this area,
with pH values below 4 and high concentrations of toxic metals, there is great uncertainty
about the quality of the water that this reservoir will store. In this work, the quality of the
water in the large reservoirs of the IPB is investigated from the analytical information of the
official quality control network (period 2008 to 2021). The reservoirs not affected by acid
mine waters (Jarrama and Corumbel) have pH values close to circumneutral and very low
concentrations of sulphates (<12 mg/L). In the reservoirs that have intermediate levels of
contamination (Andévalo and Olivargas) the pH is slightly lower, although above 7, and the
sulphate content is significantly higher (~60 mg/L). However, in the case of Olivargas, the
concentrations of some divalent metals from mining are relatively high and the values of Cd
and Zn cause that its condition is classified as ‘worse than good’. The Sancho reservoir has
a much higher level of pollution and, as a consequence, presents an average pH of 3.6 and
high concentrations of sulphates (average 184 mg/L) and toxic metals (Al, Cd, Cu, Fe, Zn,
etc.). Depending on the concentration of sulphates, it is estimated that the conditions in the
Alcolea reservoir will be similar to or worse than those in the Sancho reservoir. To ensure
a good water quality in the Alcolea reservoir, it would be necessary to eliminate 70% of the
acidic discharges in the Odiel River basin.
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