A structural analysis of the phytoplankton of the Paraná de las Palmas river (lower Paraná)
Mercado, L. M.; Gomez, N.
A structural analysis of the phytoplankton of the Paraná de las Palmas river (Buenos Aires province, Argentina) has been conducted from March 1995 to April 1996. Five structural features were assessed: species composition, species richness, species dominance, diversity, and evenness. Samples were taken every 45 days intervals at three sampling sites between km 133 and km 136 of the Paraná de las Palmas river, an arm of the lower Paraná. Physical and chemical variables (pH, temperature, dissolved oxygen, transparency) were measured and alkalinity, suspended matter and nutrients were determined at each sampling site. A total of 172 taxa were identified of which 72 belonged to Bacillariophyceae, 72 to Chlorophyceae, 16 to Cyanophyceae, and 12 to Euglenophyceae, Dinophyceae, and Chrysophyceae. Roughly one half of the total taxa is comprised of sporadic species. Diatoms were always the dominant group, attaining 81.8 % of total algae in September. Phytoplankton density was low throughout the year, with lowest values (60 cells · ml-1) during the flood, and highest (4400 cells · ml-1) during the decreasing phase. Maximum richness index was found in March 1995 (5.20) and minimum in February 1996 (1.86). Diversity index (H) varied from 1.40 to 2.38, and evenness index (E) from 0.50 to 0.73.