Chemistry, plankton and trophic state of a natural andean acid lake of volcanic origin in Patagonia

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

Copenhage, Dinamarca

Conferencia; 8° International Conference on the Conservation and Management of Lakes; 1999

The phenomenon of acidification of surface waters can result from four different processes (1): a) from sulphuric and nitric acid input through acid rain; b) due to mining activities in pyrite rich regions, c) due to acid- input by volcanic gases (SO2, SO3, HC1) and d) organic acids produced in moorland. Natural processes, as we1l as those induced by human activity, can produce identical results in lakes: mineral acidity with pH < 4, often accompanied by high concentrations of iron, sulfate and other metals like aluminum and manganese. The hydrochemistry and the ecological consequences of the acidification of lakes have been exhaustively described (2), however, the literature concentrates upon anthropogenically acidified lakes and their need for restoration (3). Taking into account the few existing data on acid lakes of volcanic origin and the limited knowledge on their behavior with respect to nutrient input from human activities, this study gives basic information which may further improve our understanding of the functioning of natura1ly acidic lakes. The information obtained may assist in developing management policies to help maintain the quality of such unusual natura1 habitats and may be applied to other sites with similar pressures. The objectives of this study are to determine trophic state, nutrient concentration, plankton composition and to consider the biogeochemical processes that operate in the naturally acidic (pH -2) lake. In the longer term, the objectives are to determine if the input of anthropogenic nutrient discharges will alter the pH and affect these natural biogeochemical cycles ( 4).