Abstract
The Iberian Pyrite Belt (IPB) hosts one of the world’s largest accumulations of acidic mine wastes and pit lakes. The mineralogical and textural characteristics of the IPB ores have favored the oxidation and dissolution of metallic sulfides, mainly pyrite, and the subsequent formation of acidic mining drainages. This work reports the physical properties, hydrogeochemical characteristics, and microbial diversity of two pit lakes located in the IPB. Both pit lakes are acidic and showed high concentrations of sulfate and dissolved metals. Concentrations of sulfate and heavy metals were higher in the Nuestra Señora del Carmen lake (NSC) by one order of magnitude than in the Concepción (CN) lake. The hydrochemical characteristics of NSC were typical of acid mine waters and can be compared with other acidic environments. When compared to other IPB acidic pit lakes, the superficial water of CN is more diluted than that of any of the others due, probably, to the strong influence of runoff water. Both pit lakes showed chemical and thermal stratification with well defined chemoclines. One particular characteristic of NSC is that it has developed a chemocline very close to the surface (2 m depth). Microbial community composition of the water column was analyzed by 16S and 18S rRNA gene cloning and sequencing. The microorganisms detected in NSC were characteristic of acid mine drainage (AMD), including iron oxidizing bacteria (Leptospirillum, Acidithiobacillus ferrooxidans) and facultative iron reducing bacteria and archaea (Acidithiobacillus ferrooxidans, Acidiphilium, Actinobacteria, Acidimicrobiales, Ferroplasma) detected in the bottom layer. Diversity in CN was higher than in NSC. Microorganisms known from AMD systems (Acidiphilium, Acidobacteria and Ferrovum) and microorganisms never reported from AMD systems were identified. Taking into consideration the hydrochemical characteristics of these pit lakes and the spatial distribution of the identified microorganisms, a model explaining their geomicrobiology is advanced.
Highlights
The peculiar ecology and physiology of extremophiles and the environments in which they develop have interested microbiologists since their discovery
In mining areas where sulfur-containing ores are brought to the surface, oxidation of sulfides by acidophilic chemolithotrophic bacteria often leads to the formation of highly acidic, metal-laden waters [7] known as Acid Mine Drainage (AMD)
We identified microorganisms associated with AMD, we could not detect iron oxidizing bacteria characteristic of AMD systems, such as Leptospirillum spp. or At. ferrooxidans
Summary
The peculiar ecology and physiology of extremophiles and the environments in which they develop have interested microbiologists since their discovery. Environments below pH 3 are not abundant They are mainly associated with two phenomena: volcanic and hydrothermal activities (e.g. hot sulfur springs, hot spots) or metal and coal mining activities [5]. Conventional and molecular microbial ecology studies have shown that both sulfur- and iron-oxidizing bacteria, such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, are present in the AMD ecosystems [6,8,9] Members of these genera are frequently found in metal-rich acidic environments associated with metal sulfide leaching, i.e. hydrometallurgy operations or AMD generating systems [4,10,11]
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