Limnological conditions shaping phytoplankton community in two subtropical cascading reservoirs

Ana Paula Vestena Cassol, Maria Angélica Oliveira, André Luis Domingues, Waterloo Pereira Filho, Mariana Durigon, Juliana Ferreira da Silva


A series of dams along the course of a river forms a cascading reservoir system. In South America the number of such systems built for hydropower generation has been increasing significantly, and a better understanding of phytoplankton communities in these habitats is needed. This study was designed to investigate spatial and temporal patterns of phytoplankton communities and limnological variables in the reservoirs of Ernestina and Itaúba, located in the high course of the river Jacuí, Rio Grande do Sul state, Brazil. Field work was carried out seasonally from January 2012 to February 2013 with samples collected from four sites in each reservoir and also three depths at each site. The sampling sites were determined according to three zones - river, transition zone and lake. 91 phytoplankton species were identified in Ernestina and 130 in Itaúba. Species richness increased with higher rainfall and cell densities were higher at longer hydraulic retention times. Thermal stratification was also an important variable shaping phytoplankton. There were no significant differences in vertical or horizontal patterns; instead, the community responded to seasonal changes. We concluded that seasonal variation is stronger than spatial patterns - division in three zones, river, transition and lake – in these reservoirs, regarding phytoplankton communities. Furthermore, Itaúba has high potential of becoming eutrophic, indicated by the repeated incidence of dinoflagellate blooms.


reservoir; subtropical; microalgae; mixing; stratification

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Departamento de Ecologia – IB - UNESP/Rio Claro. Avenida 24 A n° 1515. CEP 13506-900. Rio Claro (SP) / Brasil