Phytoplankton of two Araucanian lakes of differing trophic status (Argentina)

The Araucanian lake district in southern South America encompasses many great lakes of glacial origin, as well as a large number of smaller lakes. In this study, we present data on two waterbodies, one large (Nahuel Huapi), and one shallow (Verde). The phytoplankton community structure and dynamics or either lake were monitored for a year, in relation to the physical and chemical fluctuation, as well as the morphometry of the respective basins. In the large lake, the phytoplankton biomass was strongly dominated by diatoms (Aulacoseira granulata, Rhizosolenia eriensis and Cyclotella stelligera) and by dinoflagellates (Gymnodinium and Peridinium spp.). In the small lake, Verde, the dominant algae were Trachelomonas spp. and Cosmarium punctulatum, during the summer biomass maximum, and Rhodomonas lacustris, Chrysochromulina parva and Navicula spp. during autumn. The maximum biomass value was 634 mg m(-3) in Lake Nahuel Huapi in spring and 7800 mg m(-3) in Lake Verde in summer. According to their phytoplankton and physical and chemical features, Lakes Nahuel Huapi and Verde are readily classifiable, as ultra-oligotrophic and mesotrophic, respectively.