Cyanobacteria, microcystins and cylindrospermopsin in public drinking supply reservoirs of Brazil.
In this study, the structure of phytoplankton communities in reservoirs with constant cyanobacteria blooms was evaluated using stability, persistence and species richness analyses. Samples were collected monthly from three reservoirs in northeastern Brazil between February 2012 and January 2013. The phytoplankton taxa were quantified under an inverted microscope. Stability was measured using Spearman’s coefficient, based on the analysis of abundance rankings; persistence was measured using the inverse calculation for turnover; and richness was calculated using the number of species. Statistical analyses were used to determine the influence of abiotic variables on persistence and stability, and correlations were performed between persistence and stability and between species richness and stability. Cyanobacteria, particularly Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju, were observed in all samples. The results showed that stability and persistence were high, whereas species richness was low in the reservoir communities. The nutrients nitrate, nitrite and orthophosphate influenced persistence, whereas pH and ammonium explained stability. Persistence and stability were not significantly correlated, but a negative correlation was observed between species richness and stability.