Nictemeral variation of phytoplanktonic assemblages in a tropical reservoir (Corumbá reservoir, Goias State, Brazil), during two periods of the hydrological cycle - DOI: 10.4025/actascibiolsci.v28i1.1054

Abstract

In this study, the main environmental variables that determined the vertical distribution of phytoplanktonic assemblages in the Corumbá Reservoir (Goias) were assessed in a nictemeral scale. Samples were taken during the rainy (April 1997) and the dry (September 1997) periods, in the lacustrine zone of the Reservoir. Composition, density and biomass of phytoplanktonic assemblages were analyzed. Low biomass values were registered in both nictemeral cycles in conditions of low nutrient concentrations and low light availability, particularly in April, when the water retention time was ten days. Phytoplanktonic organisms were especially concentrated at the euphotic zone, during the morning, except for the Cylindrospermopsis raciborskii, which was concentrated at the aphotic zone due to hydraulic gradient. The low values registered in the two nictemeral cycles were mainly due to morphometric and sedimentologycal factors, and low water retention time in the Corumbá reservoir