Structure and dynamics of the phytoplankton community downstream and upstream Corumbá reservoir, Caldas Novas, state of Goiás, Brazil

Abstract

Although phytoplankton plays an important role in the trophic web of lotic environments, studies on potamoplankton in Brazil are still scarce. The present study aims at characterizing the phytoplankton community in stations upstream and downstream Corumbá reservoir in the state of Goiás, and at identifying the main environmental variables that influence its structure. Samples of sub-surface water were collected monthly in 3 stations (2 upstream Corumbá reservoir and 1 downstream), from November 1996 to November 1997, and bimonthly from January 1998 to May 1999. The distribution pattern of phytoplankton was analyzed through the limnological factors of water temperature, flow, turbidity, electric conductivity, reactive soluble phosphorus, ammonium, nitrate, and total Kjeldahl nitrogen, using canonical correspondence analysis. Among the 162 taxa identified, Cyanophyceae and Bacillariophyceae were the most abundant and were responsible for density peaks. During the study period, the largest phytoplankton density (28.313 ind.ml^-1) registered in the Corumbá river occurred in the station lying downstream the reservoir, with the dominance of the diatom Achnanthes minutissima. The heterocytous cyanoprokaryote Cylindrospermopsis raciborskii presented high abundance in the stations upstream the reservoir during the dry season. Variations showed a sharp seasonality related to the hydrological cycle, or rather, the lowest phytoplankton density occurred in the period of largest flow and maximum abundance was registered during reduced flow. Therefore, the dynamics of the phytoplankton community was strongly determined by the flow, temperature and nutrient concentrations of the Corumbá river