title: The role of a cascade of reservoirs and seasonal variation in the phytoplankton structure in a tropical river.
abstract: This study aims to analyse the influence of a cascade of reservoirs on the density, richness and functional groups of phytoplankton in the Contas River, a tropical river of Brazil. This river has two dams along its course, forming the Pedra and Funil reservoirs. Samples were collected over three consecutive years (Dec., 2007 to Dec., 2010) at 28 sampling stations along the river. We identified 198 species and the stretches downstream from the reservoirs showed greater richness. Chlorophyceae, followed by Bacillariophyceae and Cyanophyceae were the dominant groups and highest density was recorded during the rainy season. Overall, a longitudinal pattern in algal densities was found for both seasons, with the lowest values recorded in sections of the Pedra and Funil reservoirs and the highest densities in the downstream sections. Nine functional groups were identified (C, F, J, MP, S1, Sn, Td, Y, Ws); of these, F and J grouped the species with the highest relative abundance during the dry season, while the S1 group, represented by the cyanobacterium Planktothrix agardhii, was dominant in the rainy season. The present study showed a high longitudinal variation in the phytoplankton richness and density, attributed to the hydrological change between the lotic and lentic stretches. Furthermore, the effects of the cascade of reservoirs on phytoplankton, such as reduced density, increased richness and changes in algal associations, were strongly influenced by habitat heterogeneity found in this environment, as well as the rainfall in the region.
authors.affiliation: Área de Botânica, Departamento de Biologia, Universidade Federal Rural de Pernambuco - UFRPE, Rua D. Manoel de Medeiros, s/n., Dois Irmãos, CEP 52171-030, Recife, PE, Brazil. ariadne_moura@hotmail.com
authors.forename: A N
authors.initials: AN
authors.lastname: Moura
authors.forename: J S
authors.initials: JS
authors.lastname: Severiano
authors.forename: N K A
authors.initials: NK
authors.lastname: Tavares
authors.forename: E W
authors.initials: EW
authors.lastname: Dantas
mesh_terms: D044822:Biodiversity; D018533:Biomass; D001938:Brazil; D004784:Environmental Monitoring; D010839:Phytoplankton / Q000145:classification*; D011156:Population Density; D011157:Population Dynamics; D045483:Rivers; D012621:Seasons; D014872:Water Movements