Comparative eutrophication development in two Brazilian water supply reservoirs with respect to nutrient concentrations and bacteria growth

The paper presents a comparative study of two water supply reservoirs situated in different climatic regions: Gavião is located in the northeastern part of Brazil (semi-arid climate) while Vargem das Flores, situated in the southeastern part of the country, is subjected to a wet climate. Both reservoirs present blooms of cyanobacteria, which can severely impair the water quality. Emphasis is given here on evaluation of phytoplankton growth, together with the study of the N/P ratio in the water body. In spite of the prevalence of high N/P values in Vargem das Flores, there is a clear trend in the dominance of cyanobacteria in the phytoplankton, which contradicts results from researches in temperate aquatic environments. Some management strategies for both reservoirs are discussed. They are focused on selected water treatment process and on the implementation of techniques to avoid the abstraction of eutrophic waters into the system (air curtain, plastic barriers).