Periodic disturbances, trophic gradient and phytoplankton characteristics related to cyanobacterial growth in Guarapiranga Reservoir,Sao Paulo State, Brazil

摘要

The relationships between phytoplankton assemblage, disturbance and trophic characteristics were investigated in Gurarapiranga Reservoir,which supplies water water to approximately 25% of the Sao Paulo metroplitan region. Two open-water stations were sampled weekly during 1991-92,in order to determine the main factors promoting of Cyanobacterial growth. These were found to include:rainfall-induced nutrient inputs via runoff and percolation from the drainage basin;criculation patterns that favored resurgence of nutrients and transported littoral algae to the open water;senescence of algae (especially Chlorococcales and Zygnemaphyceae) which increased the availability of nutrients in the water column;and high nutrient concentrations during the driest season. Restricting nutrient inputs and controlling eutrophication are necessary if the quality of water supplied from this reservoir is to be improved.