Publicado em "Proceedings of the Energy and Environment Knowledge Week 2014(E2KW2014)". ISBN 978-84-697-1162-

Almeida, S.

De la Torre, M. L.

Delgado, C.

Gomes, P.

Grande, J. A.

Rivera, M. J.

Santistebán, M.

Valente, Teresa Maria Fernandes

Universidade do Minho: RepositoriUM

  Energy and Environment Knowledge Week - E2KW 2014 -      DISTRIBUTION AND ROLE OF BENTHIC DIATOMS AS INDICATORS OF ACID MINE DRAINAGE IN AFFECTED WATER DAMS  T. Valente 1,2, M.J. Rivera1, 2, S. Almeida3, C. Delgado3, P. Gomes1,2, J.A. Grande2, M.L. de la Torre2, M. Santisteban1,2  1 Centro de Investigação Geológica, Ordenamento e Valorização de Recursos (CIG-R), Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal 2 CIPIMS, Universidad de Huelva, Campus de la Rábida, Huelva, Spain  3 GEOBIOTEC, Universidade de Aveiro 3810-193 Aveiro, Portugal.  E-mail: teresav@dct.uminho and teresav@dct.uminho 135  Energy and Environment Knowledge Week - E2KW 2014 -     DISTRIBUTION AND ROLE OF BENTHIC DIATOMS AS ACID MINE DRAINAGE INDICATORS IN AFFECTED WATER DAMS  1. Purpose In mining regions the presence of water reservoirs affected by acid mine drainage (AMD) is a common problem. It is known from scientific literature that AMD produces structurally simple ecosystems dominated by acidophilic and acid-tolerant organisms, either prokaryotes or eukaryotes. From a monitoring perspective, the algae communities, namely the diatoms, are among the most effective ecological indicators of AMD conditions. This work presents a combination of geochemical, mineralogical and ecological data obtained in water reservoirs located in one of the most paradigmatic mining regions, suffering from AMD problems: the Iberian Pyrite Belt (IPB). Four water reservoirs located in the same territory – the Spanish sector of the IBP, but storing water for different purposes, were selected to achieve an environmental classification based on the effects by AMD: two mining dams (Gossan and Águas Ácidas), a reservoir for industrial use (Sancho), and one with water used for human supply (Andévalo). The main goal was to characterize the distribution of benthic diatoms, namely in relation with hydrochemistry and sediment properties, and to understand the role of these algae as indicators of severity of AMD contamination.  2. Methodology Sampling took place at the point where the water enters in each of the reservoirs (Fig. 1). Overall hydrochemical characterization was based on mensal campaigns carried out between October 2011 and May 2012. Algae and sediments were collected in summer 2012. pH, electric conductivity (EC) and total dissolved solids (TDS) were measured in the field. Sulphate was measured by photometry. Metals concentrations in the water were determined by atomic absorption spectrometry. Mineralogical analyses of the sediments were performed by X-ray diffraction (XRD) on a Philips X’pert Pro-MPD diffractometer, using Cu-Kα radiation. The XRD diffractograms were obtained from powders (fraction <2 mm; fraction < 2 µm fraction) and from oriented aggregates (<2 µm fraction) in the interval 3 to 65º2θ and 3 to 35º2θ respectively. The finest fraction was obtained by the sedimentation method and the particle-size separation based on theoretical Stockes’ Law. The clay mineralogy was determined using the oriented preparations, which were submitted to the following treatments: air-dried, ethylene glycol (EG)-solvated, and heated (490ºC). Chemical analysis for metals and metalloids was performed in both grain size fractions by inductively coupled plasma/mass spectrometry (ICP/MS). Diatoms were sampled from sediments. Identification and quantification were performed in slides mounted with Naphrax®.   136  Energy and Environment Knowledge Week - E2KW 2014 -     3. Results and Discussion Hydrochemistry Table 1 presents the average chemical composition of the water. With the exception of Andévalo, the studied dams show typical evidences of AMD affection (low pH and high sulphate and metals contents). The higher concentrations of metals, arsenic and sulphate occur in the mining dams: Águas Ácidas and Gossan. Table 1 – Physical-chemical properties of the water Water Dam  µS/cm     mg/L      pH EC  TDS SO4 Fe Cu Zn Mn Ni As Pb ÁGUAS ÁCIDAS 3,05 7520  4820 3808 420 7,90 35,24 58,86 2,04 0,01 0,14 ANDÉVALO 6,15 364  231 130 0,67 0,22 0,06 0,32 - 0,01 - SANCHO 3,41 505  324 196 0,86 0,24 2,91 1,69 - 0,01 0,33 GOSSAN 2,78 2720  1740 936 28,58 4,70 10,64 10,33 0,12 0,01 0,06   Sediments characterization The most contaminated sediments appear in Aguas Acidas and Gossan. In general, results suggest that Pb, As, Zn and Cu accumulates in the clay size fraction ( <2 μm), especially in these two dams (Table 2). Such an accumulation may be related with the mineralogy of this finest fraction. Jarosite and goethite, which compose the typical AMD-precipitates, may be the main responsible hosts for the accumulation of trace elements in Águas  Ácidas and Gossan, respectively.  Table 2 – Chemical composition of the sediments in two grain size fractions Element (mg/kg) ÁGUAS ÁCIDAS ANDÉVALO SANCHO GOSSAN  < 2mm < 2 µm < 2mm < 2 µm < 2mm < 2 µm < 2mm < 2 µm Fe 278 140 190 701 84 000 123 661 89 280 90 172 125 826 285 997 Cu 495 1636 124 212 727 321 2 099 1 501 Zn 279 315 127 190 473 332 340 395 As 571 1830 992 1 576 283 283 643 818 Pb 29 126 65 250 125 205 162 170 584 884 S 14 529 54 857 1 210 310 4 187 604 20 897 1 792   Diatom community The study of the abundance and diversity of benthic diatoms showed that acidophilic diatoms (Pinnularia acidophila and P. aljustrelica) are dominant in the two mining dams (Águas Ácidas and Gossan), where data about hydrochemistry and sediment geochemistry put in evidence contamination by AMD. On the other hand, in Andévalo dam, dominates the specie Eunotia exigua, while acidophilic species, like Pinnularia acidophila and P. aljustrelica are rare or absent.   137  Energy and Environment Knowledge Week - E2KW 2014 -     4. Conclusions Hydrochemistry and geochemistry results indicate that the four dams are subject to the effect of metallic loads from polluted rivers, although with different levels: Águas Ácidas > Gossan > Sancho > Andévalo.  In accordance, diatom communities have differences in composition and dominant diatom taxa. Pinnularia acidophila and P. aljustrelica were found dominant in the most acidic dams (Gossan and Águas Ácidas), Pinnularia subcapitata was dominant in Sancho and Eunotia exigua in Andévalo. Therefore, the obtained results suggest the ability of diatoms to indicate different degrees of AMD affection.   138

Distribution and role of benthic diatoms as acid mine drainage indicators in affected water dams

Distribution and role of benthic diatoms as acid mine drainage indicators in affected water dams

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Universidade do Minho: RepositoriUM