Lotic and lentic environments of the Pampean Plain

SOLARI L C.; MAC DOANGH, M.E.

FRESHWATER PHYTOPLANKTON FROM ARGENTINA

CRAMER

Año: 2011;

The pampean plain have a flattened relief and temperate climate. Their landscape is characterized by a great number of shallow lakes (flushing, backwater, and seepage lakes) with different degrees of interconnection with rivers and wetlands. The Salado is the major autochthonous river of the Buenos Aires Province and is a typical lowland river. The first studies of phytoplankton in shallow lakes were published during the middle of the last century, whereas investigations on the phytoplankton of lotic environments have only been carried out since 1980. The most common groups of freshwater algae (cyanobacteria, chlorophytes, diatoms, cryptophytes, and euglenophytes) are present in the phytoplankton of the shallow lakes and rivers of the pampean plain. Nevertheless, only the cyanobacteria, chlorophytes, and diatoms present a high specific richness. In general terms, cyanobacteria and chlorophytes predominated; whereas diatoms were abundant on only a few occasions. Chlorophytes and cyanobacteria were mainly represented by euplanktonic species, whereas a high proportion of the diatoms were brought in from the periphytic and benthic communities. Numerous shallow lakes of this region are characterized by the presence of submerged and emergent macrophytes that influence the temporal and spatial variability of the phytoplankton structure because of the changes in water transparency, nutrient balance, and zooplankton structure related to macrophytes development. The shallow lakes connected to the Salado River act as an alluvial valley, incorporating organisms into the river or into the lakes, though this influence depends on the direction of the water flow that can occur during flooding conditions. The differences in the structure and dynamics of the phytoplankton of lotic and lentic environments of the pampean plain are related to the hydrological events and geomorphologic-hydrologic features, to the incorporation of inocula from connected systems, and to the colonization of submerged macrophytes. In recent years, several hydraulic constructions have been made (gates, canalizations, and other modifications) so as to modify the natural dynamic system and thus influence the natural exchange of phytoplankton assemblages in this complex system.