CECOAL   02625
CENTRO DE ECOLOGIA APLICADA DEL LITORAL
Unidad Ejecutora - UE
capítulos de libros
Título:
Phytoplankton
Autor/es:
ZALOCAR DE DOMITROVIC Y., DEVERCELLI M. AND GARCÍA DE EMILIANI M.O.
Libro:
The Middle Paraná River: Limnology of a Subtropical Wetland
Editorial:
Springer
Referencias:
Lugar: Berlin; Año: 2006; p. 177 - 203
Resumen:
 This chapter includes the whole data of the phytoplankton community and some environmental factors, covering hydrologically normal annual periods and anomalous hydrological cycles, induced by the ENSO. Most of the information is based on the main-channel, side-channels and floodplain lakes of the upstream-stretch (near Corrientes city) and the downstream-stretch (near Paraná city) of the Middle Paraná River. In the channel and the alluvial plain, the spatiotemporal changes of the phytoplanktonic community 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 alluvial plain environments. During normal hydrological periods, the channel shows typical fluvial phytoplankton, dominated by central Bacillariophyceae (Aulacoseira granulata) and, alternatively, with sub-dominance of Chlorococcales, Cryptophyceae or Cyanobacteria. In anomalous hydrological cycles, there are differences in the abundance and structure of the community, attributed to the loss of normal exchange of organisms between the main flux and the areas with higher water residence time, that function as storage zones of fluvial species. During El Niño, the channel maintains a relative homogeneity of the community, although mean density values are significantly lower than those registered in normal hydrological cycles. The dominant and sub-dominant groups change to Cryptophyceae and Bacillariophyceae, respectively. During La Niña, the scarce contribution of large Bacillariophyceae species (Aulacoseira) to density demonstrates a profound change in the community structure, probably due to the inaccessibility of inocula from other sites. Waters that drain from the upper sections of the river and that run towards plain environments by overflow, find appropriate environmental conditions (scarce horizontal flux, high thermal amplitude, high organic matter content) that favor a rapid re-organization of the phytoplanktonic community. The alluvial plain plays an essential role in maintaining algal populations and incorporating them towards or from the main flux.