A Deeper Look into the Biodiversity of the Extremely Acidic Copahue volcano-Río Agrio System in Neuquén, Argentina

The Copahue volcano-Río Agrio system, on Patagonia Argentina, comprises the naturally acidic river Río Agrio, that runs from a few meters down the Copahue volcano crater to more than 40 km maintaining low pH waters, and the acidic lagoon that sporadically forms on the crater of the volcano, which is studied for the first time in this work. We used next-generation sequencing of the 16S rRNA gene of the entire prokaryotic community to study the biodiversity of this poorly explored extreme environment. The correlation of the operational taxonomic units (OTUs)s presence with physicochemical variables showed that the system contains three distinct environments: the crater lagoon, the Upper Río Agrio, and the Salto del Agrio waterfall, a point located approximately 12 km down the origin of the river, after it emerges from the Caviahue lake. The prokaryotic community of the Copahue Volcano-Río Agrio system is mainly formed by acidic bacteria and archaea, such as Acidithiobacillus, Ferroplasma, and Leptospirillum, which have been isolated from similar environments around the world. These results support the idea of a ubiquitous acidic biodiversity; however, this highly interesting extreme environment also has apparently autochthonous species such as Sulfuriferula, Acidianus copahuensis, and strains of Acidibacillus and Alicyclobacillus.

Geochemical controls on the partitioning and hydrological transport of metals in a non-acidic river system

The speciation of metals, i.e. in which chemical form they occur, controls their mobility, bioavailability and toxicity. The overall objective of this study is to extend the knowledge on the spreading of metals in non-acidic river systems; this knowledge is currently much more limited than the knowledge on metal behavior under acidic conditions that for instance are found in acid mine drainage systems. We combine novel measurements of metal spreading under distinctly high-pH conditions (up to 9.6) in the Tuul River at the Zaamar Goldfield mining site (Upper Lake Baikal Drainage Basin, Mongolia) with a geochemical modelling approach (Visual MINTEQ). Total mass flows of several metals (Al, Cd, Fe, Mn, Pb and V) showed net increases over the mining site, with metals in suspension generally dominating the total export from the site. Model results showed that a main difference from acid mine drainage geochemistry is that the prevailing high pH causes precipitation of ferrihydrite and gibbsite, which removed between 90 to 100% of Fe and Al from solution. This notably influenced the behavior of As, Pb and V since their solubilities are controlled by sorption onto ferrihydrite. The combined effects from such geochemical processes (precipitation, sorption) hence explain the high impact of suspended transport to total transport under high pH conditions. Arsenic furthermore showed dissolved concentrations above health risk-based guideline values in several locations and can thus be of main toxic concern in the upper Lake Baikal Drainage Basin. Moreover, present modelling showed that in particular the solubility of Fe, Pb and Zn can increase considerably as DOC concentrations increase due to metal-organic complexation. In high pH systems, seasonality of DOC concentrations can therefore have a major influence on the spreading and toxicity of these metals, as can DOC trends caused by land use change. Present results also suggest that the behavior of Cr, Cu and Mo would be much better understood if a dependable adsorption database for hydroxyapatite could be developed.