Phytoplankton composition of the Itaparica and Xingo reservoirs, Sao Francisco River, Brazil/Composicao fitoplanctonica dos reservatorios de Itaparica e Xingo, Rio Sao Francisco, Brasil

The installation of dams causes changes to the integrity of rivers and to the water cycle, performing an instrumental role in the organization of biological communities, including that of phytoplankton. In the present study, we analyzed the taxonomic composition of phytoplankton in two hydroelectric reservoirs on the Sao Francisco River, Itaparica and Xingo reservoirs. Samples were collected at quarterly intervals between December 2007 and September 2009, at 12 sampling stations in each reservoir, totaling 92 samples. We identified 110 species in the Itaparica reservoir and 136 in the Xingo reservoir, of which diatoms followed by green algae, played a major contribution to both reservoirs. Most of the species is rare and/or occasional. In the Itaparica reservoir, there were no very frequent species, although in the Xingo this category was represented by the diatoms Aulacoseira granulata (Ehrenberg) Simonsen and Fragilaria crotonensis Kitton. These results show that, despite the similarity in the composition of phytoplankton, the reservoirs studied certainly differed regarding their environmental conditions.