The Copahue-Caviahue system (37° 53’ S, 71° 02’ W): nutrients (C, N, P), sediments and acidophilic algae

BAFFICO, G.; BEAMUD, G.; DIAZ, M.; PEDROZO, F.; TEMPORETTI, P.

San Carlos de Bariloche, Río Negro, Argentina

Simposio; 18th Internacional Biohydrometallurgy Symposium; 2009

The aim of this work is summarize the 10-years information about the 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 = 2.0, to the neutrality 40 km downstream the lake. The TP concentration of the Agrio River spans almost two orders of magnitude from its source (40 mgP/L) to the inflow to the lake (1.8 mgP/L). The N concentrations were 10 times lower, mainly as ammonium. The P exported of the Upper basin, the TP lake concentration (240-500 ugP/L) and the SRP:TP ratio (0.50-0.95) increased following the volcanic activity. The Caviahue Lake receives 40-200 Tons P/yr and 14 Tons N/yr, being the Agrio River the main contributor (P=98%; N=71%). In the sediments, the main P-fraction is bounded to Organic Matter 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 Agrio River receives tributaries of different chemical characteristics producing effects on its waters (pH increase and conductivity decrease). The dilution in element concentrations (S, Cl, Ca, Fe, Al and P) is the main process, but the precipitation of Fe and Al also produce changes in the structure and biomass of the algae. Biomass and species diversity of the periphyton tend to increase along this acid-neutral gradient of the river.