Enrique López Pamo

Geomicrobiology of La Zarza-Perrunal Acid Mine Effluent (Iberian Pyritic Belt, Spain)

ABSTRACT Effluent from La Zarza-Perrunal, a mine on the Iberian Pyrite Belt, was chosen to be geomicrobiologically characterized along a 1,200-m stream length. The pH at the origin was 3.1, which decreased to 1.9 at the final downstream sampling site. The total iron concentration showed variations along the effluent, resulting from (i) significant hydrolysis and precipitation of Fe(III) (especially along the first reach of the stream) and (ii) concentration induced by evaporation (mostly in the last reach). A dramatic increase in iron oxidation was observed along the course of the effluent [from Fe(III)/Fetotal = 0.11 in the origin to Fe(III)/Fetotal = 0.99 at the last sampling station]. A change in the O2 content along the effluent, from nearly anoxic at the origin to saturation with oxygen at the last sampling site, was also observed. Prokaryotic and eukaryotic diversity throughout the effluent was determined by microscopy and 16S rRNA gene cloning and sequencing. Sulfate-reducing bacteria (Desulfosporosinus and Syntrophobacter) were detected only near the origin. Some iron-reducing bacteria (Acidiphilium, Acidobacterium, and Acidosphaera) were found throughout the river. Iron-oxidizing microorganisms (Leptospirillum spp., Acidithiobacillus ferrooxidans, and Thermoplasmata) were increasingly detected downstream. Changes in eukaryotic diversity were also remarkable. Algae, especially Chlorella, were present at the origin, forming continuous, green, macroscopic biofilms, subsequently replaced further downstream by sporadic Zygnematales filaments. Taking into consideration the characteristics of this acidic extreme environment and the physiological properties and spatial distribution of the identified microorganisms, a geomicrobiological model of this ecosystem is advanced.

Iron terraces in acid mine drainage systems: A discussion about the organic and inorganic factors involved in their formation through observations from the Tintillo acidic river (Riotinto mine, Huelva, Spain)

Iron terraces that form in acidic mine drainage settings are unique and extreme geomicrobiological systems that can provide highly relevant information about the interaction between microbes and their surrounding aqueous environments. These singular systems can represent, additionally, potential models for the study of ancient geological formations (e.g., banded iron formations, stromatolites) and/or for the cycling of iron on Mars. This work describes geochemical, mineralogical, morphological, and microbiological evidence obtained in the highly acidic and Fe-rich Tintillo River (Riotinto mines, Huelva, SW Spain), which can be used to speculate about the origin and nature of the terraced iron formations (TIFs) that are being currently formed in acid mine drainage environments. The size (up to 36 m long and 1 m thick) and continuity (strong development over 3.5 km) of the iron terraces offer a unique opportunity to study the different organic (mainly microbial) and inorganic processes involved in the construction of these characteristic, travertine-like, sedimentary structures. Evidence presented in this study suggests that both types of processes appear to be controlling factors in the formation and internal arrangement of the TIFs, although no defi nitive evidence has been found to support the prevalence of any of these mechanisms with respect to another. The photosynthetic production of dissolved oxygen by eukaryotic microorganisms (green algae, euglenophytes, and diatoms) and the Fe-oxidizing metabolism of acidophilic prokaryotes are critical factors for the formation of TIFs, whereas abiotic parameters, such as water composition, fl ow rate and velocity, or stream channel geometry, also appear to be essential variables.