Cold-temperate lakes of South America: do they fit northern hemisphere models?

Abstract

Comparative studies on cold-temperate lakes on a worldwide basis have often neglected this lake category in the southern hemisphere. This study describes and analyzes the main limnological characteristics of 54 Argentine Patagonian lakes located between 38° and 55° S latitude. By principal components analysis of summer data, three basic types of Patagonian lakes were identified: Andean, ecotone and plateau. These groups were distributed across a gradient defined mainly by trophic and edaphic characteristics, and secondarily by lake morphometry and climatic factors. Most lakes deeper than 50m showed summer stratification, with a mean thermocline depth of 38 m. Thermocline depth showed a direct correlation with latitude. The best single predictors of thermocline depth were fetch and lake area. Thermocline depth was not only deeper than predicted by northern hemisphere models, but also deeper than in other southern hemisphere lakes of similar surface area located in Chile and New Zealand. Surface water temperatures were correlated with latitude. Only northern Patagonian lakes showed significant differences in surface water temperatures on both sides of the Andes. The best single predictors of chlorophyll were Secchi disk depth and mean depth. Models from the literature overestimated chlorophyll concentrations for Argentine Patagonian lakes, particularly under eutrophic conditions. We suggest that cold-temperate lakes in Argentina differ in their thermal regime from northern hemisphere lakes at equivalent latitudes, owing to the marked oceanic influence on the southern hemisphere land mass, together with the strong and persistent westerly winds. These features coupled with lower nutrient contents make the use of global models inadequate for Argentine cold-temperate lakes.