Ecological status assessment of tropical reservoirs through the assemblage index of phytoplankton functional groups

The study assessed the ecological status of water supply reservoirs with different trophic states through the phytoplankton assemblage index (Q index). Integrated water and phytoplankton sampling were collected in euphotic zone of five tropical reservoirs (Upper Tiete river basin, Sao Paulo, Brazil) in the summer and winter (2010). Biovolume of functional groups was determined, and the Q index was applied at each site of the reservoirs. The composition of functional groups and biomass changed between the reservoirs and between the climatic periods. From upstream to downstream of the basin, the reservoirs showed the following qualification: Ribeirao do Campo (ultra-oligotrophic-excellent to good), Ponte Nova (oligotrophic-good), Paraitinga (mesotrophic-medium), Jundiai (meso-eutrophic-medium to tolerable), Taiac, upeba (mesotrophic-tolerable to bad). Q index was significantly correlated with trophic state index (r = -0.81). Linear regression showed that Q index tended to decrease with the increasing in TP concentration. We conclude that the phytoplankton assemblage index showed consistently the spatial and temporal variation of the ecological status of different reservoirs in the study period. Our results evidenced that this biotic index can be a useful tool for monitoring and assessment of the ecological conditions of tropical reservoirs.