First results on water chemistry, algae and trophic status of an andean acidic lake system of volcanic origin in Patagonia (Lake Caviahue).

PEDROZO, F.; KELLY, L.; DIAZ, M.; TEMPORETTI, P.; BAFFICO, G.; KRINGEL, R.; FRIESE, K.; MAGES, M.; GELLER, W.; WOELFL, S.

HYDROBIOLOGIA

Kluwer Academic Publishers

Año: 2001 vol. 452 p. 129 - 137

0018-8158

The acidic caldera lake Caviahue (Patagonia, Argentina) and its main tributaries were studied during September 1998. The main results are: the acidity of the Lake Caviahue (pH 2.56, acidity: > 5 mmol H+ l-1) is controlled by the extremely acidic Upper Rio Agrio (pH 1.78, acidity: > 20 mmol l-1). The high sulphate contents of the river and the lake can be attributed to sulphuric acid generated from the uptake of sulfur gases in the crater lake of volcan Copahue at approximately 2800 m a.s.l. The high concentrations of both Fe and trace metals (e.g. Cr, Ni, Zn) in Lake Caviahue originate from the chemical interaction of sulphur-acidic volcanic solutions with the predominantly volcanic geology of the catchment area flowpath. Due to the water-rock interaction with the P-rich andesitic rocks both the acidic Rio Agrio and Lake Caviahue have high phosphorous concentrations (300-500 µg P l-1) indicating a high eutrophic potential. The plankton community was reduced to bacterioplankton, phytoplankton and rotifers. The phytoplankton was dominated by one green alga, Keratococcus raphidioides (> 90% of total abundance) followed by Lobosphaera sp. (Chlorella) and Chlamydomonas sp. The total phytoplankton density was about 15,000 cells ml-1 in the upper 10 m water column. Rotifers consisted of one bdelloid species. Its abundance was highly variable between 380 and 4040 ind l-1. In the Upper and Lower Rio Agrio, the epilithic community was dominated by one chloroccocal and two Ulothricales. According to standard trophic categories based upon phytoplankton densities and P concentrations, Lake Caviahue can be classified as mesotrophic/eutrophic. However, chlorophyll a concentration indicates ultraoligotrophic conditions which can be related to an unfavourable underwater light climate (SD = 3 m).