Phytoplankton of the Paraná River Basin

DEVERCELLI, MELINA; ZALOCAR DE DOMITROVIC YOLANDA; FORASTIER MARINA E.; MEICHTRY DE ZABURLÍN

Fitoplancton de Argentina

CRAMER

Año: 2012;

 This chapter summarizes the information on the phytoplankton of the Paraná River in the Argentine stretching density, biomass, functional groups and diversity studies of the main channel and floodplain since the 70´s. We described the Yacyretá dam and its impact downriver since it started operating in September 1994. The spatio-temporal changes of the phytoplankton are associated to the hydrosedimentological regime. Regular variations in the hydrological phases, and shorter permanent fluctuations are essential for phytoplankton maintenance, since they allow the lateral exchange with zones of higher algal accumulation in the own channel and with the floodplain. During ordinary hydrological cycles, the mainstem shows a typical potamoplankton, dominated by Aulacoseira granulata and, alternatively, with sub-dominance of Chlorococcales, Cryptophyceae at the Middle and Lower Stretch, Cyanobacteria abound at Yacyretá reservoir and downriver at the High and the beginning of the Middle stretch., Since the disruption of Yacyretá Reservoir, there were profound changes in the High Paraná  phytoplankton evidenced in increased density and replacement of dominant species; Cryptophyceae replaced the Bacillariophyceae. Since 2001, water transparency increased and phosphorus concentration decreased, as well as the density and diversity of phytoplankton. Since 2004, an increase in Cyanobacteria was observed with bloom of Microcystis aeruginosa that extended 220 km downstream of the dam. Anomalous hydrological cycles, related to the ENSO (El Niño Southern Oscillation) phenomenon produced differences in the density and structure phytoplankton. During El Niño, the mainstem maintains a relative homogeneity of the community, although mean density values are significantly lower than those registered in ordinary hydrological cycles. La Niña provokes a more drastic change in the community, due to the disruption in the exchange with the alluvial valley. The river-floodplain connectivity is essential for the maintenance of phytoplankton diversity.