CONICET | Buscador de Institutos y Recursos Humanos

The aim of this work is to summarize the 10-years information about the ecological studies in the naturally acidified area which includes the Copahue Volcano, the Upper Rio Agrio, the lake Caviahue and the Lower Rio Agrio. The river has a strong pH gradient, from the source (pH 0,8), entering in the Caviahue lake at pH » 2, to the neutrality . The TP concentration of the Agrio River spans almost two orders of magnitude from its source to the inflow to the lake. The N concentrations were 10 times lower, mainly as ammonium. The P exported of the basin (2500 KgP/Km2/yr), the TP concentration and the SRP:TP ratio increased following the volcanic activity. The Caviahue Lake receives 245 Tons P/yr and 21 Tons N/yr, being the Agrio River the main contributor (P=98%; N=71%). In the sediments, the main P-fraction is bounded to OM showing high correlations between TP and C. Biodiversity is very low as a result of extreme environmental conditions, being the Chlorophyceae the prevailing algae group. Phytoplankton is nitrogen limited and has the capacity to use alternative sources of Carbon, different of CO2. The high affinity of the microalgae for CO2 and the apparent absence of a Carbon Concentration Mechanisms, suggests that photosynthesis and growth rates are unlikely to be limited by CO2. The algal biomass and species diversity of the periphyton surveyed along an acid-neutral gradient of the Agrio River showed that pH increased and conductivity decreased as the Agrio River receives tributaries of different chemical characteristics. The dilution of concentration of the elements (SO4, Cl, Ca, Fe, Al and TP) is the main process, but the precipitation of a Fe and Al occurs as a consequence of the pH increase producing changes in the structure and biomass of the algae.

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