Twenty-three water dams located in the Iberian Pyrite Belt were studied during March 2012 (early spring) in order to carry out an environmental assessment based on diatom communities and to define the relationships between these biological communities and the physico-chemical characteristics of the dam surface water. This is the first time that a diatom inventory has been done for dams affected by acid mine drainage (AMD) in the Spanish part of the Iberian Pyrite Belt (IPB). It was found that the pH was the main factor influencing the behaviour of the diatom communities. Then, using a dbRDA approach it was possible to organize the aggrupation of diatoms into four groups in response to the physico-chemical conditions of the ecosystem, especially pH: (1) Maris, Aac, Gos, Cmora (pH 2–3); (2) Andc, San, And, Dpin (pH 3–4.5); (3) Gran, Pleon, Oliv, Lagu, Chan, SilI, SilII, Joya, Gar, Agrio, Camp, Corum (pH 4.5–6); (4) Herr, Diq I, Diq II (pH 6–7). The obtained results confirmed the response of benthic diatom communities to changes in the physico-chemical characteristics of surface water, and helped to understand the role of diatoms as indicators of the degree of AMD contamination in those 23 dams. Special attention was given to those that have an acidophilic or acid-tolerant profile (pH 2–3 and pH 3–4.5) such as Pinnularia aljustrelica, Pinnularia acidophila, Pinnularia acoricola and Eunotia exigua, which are the two groups found in the most AMD contaminated dams.

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Acid Mine Drainage (AMD) results from sulfide oxidation, which incorporates hydrogen ions, sulfate, and metals/metalloids into the aquatic environment, allowing fixation, bioaccumulation and biomagnification of pollutants in the aquatic food chain. Acidic leachates from waste rock dams from pyritic and (to a lesser extent) coal mining are the main foci of Acid Mine Drainage (AMD) production. When AMD is incorporated into rivers, notable changes in water hydro-geochemistry and biota are observed. There is a high interest in the biodiversity of this type of extreme environments for several reasons. Studies indicate that extreme acid environments may reflect early Earth conditions, and are thus, suitable for astrobiological experiments as acidophilic microorganisms survive on the sulfates and iron oxides in AMD-contaminated waters/sediments, an analogous environment to Mars; other reasons are related to the biotechnological potential of extremophiles. In addition, AMD is responsible for decreasing the diversity and abundance of different taxa, as well as for selecting the most well-adapted species to these toxic conditions. Acidophilic and acidotolerant eukaryotic microorganisms are mostly composed by algae (diatoms and unicellular and filamentous algae), protozoa, fungi and fungi-like protists, and unsegmented pseudocoelomata animals such as Rotifera and micro-macroinvertebrates. In this work, a literature review summarizing the most recent studies on eukaryotic organisms and micro-organisms in Acid Mine Drainage-affected environments is elaborated.

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A procedure to automatically correlate well logs measured in boreholes that are located in continental siliciclastic basins by using two different methods is shown. The first method is applied to the parametric layers that were determined in each borehole starting from the values of their geophysical parameters and consists of correlating, by cross-association, the columns formed by these layers. The second method consists of cross-correlating the geophysical stretches or units, which are established as sets of layers with similar characteristics that are sufficiently different from the average values in the adjacent stretches. The evaluation of the correlation results requires showing the criteria that are used for determining the parametric layers that are obtained from the well logs, the result of which is called segmentation in this study. This evaluation also requires to show the techniques that are used to determine the geophysical stretches by a process that is called stretching in this study. The reason for using different correlation methods is that cross-association of layers provides high resolution but relatively smaller spatial extent, whereas cross-correlations of geophysical stretches provide higher spatial extent but lower resolution. Thus, the cross-association results have been used both to assess the correlations in boreholes that are relatively close (distances<10 km) and to support the establishment of the stretch correlation criteria. The developed methodology is applied to a set of boreholes located in the Duero Basin (Spain). From the results obtained, an evaluation of the correlations with respect to the distances between boreholes was carried out. Furthermore, it is shown that the correlations between geophysical stretches enable identifying the correspondences between these and the tectono-sedimentary sequences (activation-relaxation of a tectonic phase) that are established in the literature.