Duplicado disponible en caja 16 no 19 de INICNE

This paper deals with the principal limnological features of the Totora and González ponds, selected among those belonging to the Riachuelo River basin for their ineresting and contrasting general characteristcs. The study has been carried out along an annual cycle by means of monthly sampling operations, considering the main physical and chemical properties, the phytoplankton, zooplankton, benthos, fish populations, as well as the primary production and related parameters. According to the obtained data, such water bodies present extreme trophic conditions. The Totoras pond is of moderate eutrophy, with high biotic diversity, clear water, great part of the bottom colonized by submerged macrophytes and psammitic algae with a thick cover of organic detritus in the central area although the dissolved oxigen was never less than 50% saturation. The profile of primary production shows good development in depth, having the maximun rate of carbon fixation at 1 or 2 meters and phtosynthetic inhibition in a superficial layer. The Gonzalez pond, by the contrary, is largely euthrophic, with very turbid waters, bottom without macrophytes, low biotic diversity, and a practically constant bloom of blue green algae. The dissolved oxigen was reduced to the bottom but without exhaustation because of the wind action. The primary production of phytoplankton was very high but restricted to the upper layer