PHYTOPLANKTON OF YACYRETÁ RESERVOIR (ARGENTINA-PARAGUAY) AFTER A DECADE FROM ITS FILLING

Abstract

In this study, the structure and dynamics of the phytoplankton of Yacyretá Reservoir and its relationship with main limnological variables between December 2004 and November 2005, ten years after the filling of the reservoir, was studied. Qualitative and quantitative samples were collected at six sampling stations, following a longitudinal zonation criterion. Density, composition, specific richness, diversity, equitability, relative frequencies, and dominance were analyzed. During the studied period, the Yacyretá Reservoir did not present thermal stratification, and the dissolved oxygen concentration in the water column was high. Two hundred species in 9 algae classes were recorded. The species number per sample varied between 14 and 45 taxa and the specific diversity between 1.55 y 4.61 bits. Density ranged between 66 and 10060 ind/ml, with dominance of Bacillariophyceae and Cryptophyceae in different regions of the reservoir. An increase in the Cyanobacteria density at the begining of autumn and at the end of the spring, mainly in the stations with longer time of permanence of water, was recorded. During the analysis period the composition and density of the phytoplankton presented a noticeable spatial and temporal variation, determined mainly by the hydrosedimentologic cycle variations.