The acidic waters of Rio Agrio and Lago Caviahue at Volcan Copahue, Argentina

Many active volcanoes are sources of highly acidic waters that originate from volatile mineral acids. Several crater Iakes and volcanic acid brines were chemically characterized (VAREKAMP et al. 200 l), showing a broad spectrum of dissolved elements, many heavy metals, and high temperatures (for more information on crater lakes and constraints in their physical and chemical properties see PASTERNACK & VAREKAMP 1997, VAREKAMP et al. 2000; for volcanoes and activities see JENSEN 2002). eopahue Volcano in Argentina has a crater lake near the summit at 2 700 m a.s.l. Ri o Agri o i s an acidic river emerging from a geothermic source below the crater lake at the flank of eopahue volcano (DE MooR et al. 2003). The 13-km Upper Ri o Agri o flows in to a glacial finger-lake, Lake eaviahue (l 600 m a. s. l.), the outflow o f which is the Lower Ri o Agri o. The system o f river stretches an d lakes ( Fig. l) shows an acidity gradient from p H O to 7 (PEDROZO et al. 200 I). The extreme chemistry along this gradient o f acidity was studied with an additional focus on microbiology and planktonic and epilithic algae.

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