Influence of climatic conditions on cyanobacteria blooms in a tropical water supply river (Rio das Velhas, Brazil)

The paper presents a discussion about the striking influence of climatic conditions on the onset of cyanobacteria blooms in a warm water river in Brazil. An unusual drought period has been observed in the second half of 2007 in Rio das Velhas, Brazil, which led to an unexpected bloom of bluegreen algae (cyanobacteria). Cyanobacteria blooms constitute a special concern in Brazil, since the first human deaths caused worldwide by cyanotoxins have been reported in this country. The Brazilian legal framework restricts the water abstraction under such conditions and imposes a special monitoring programme to be carried out by water supply companies. The results of water quality analysis point out the conjunction of two factors as the main cause of the mentioned cyanobacteria blooms: nutrients input from treated and untreated sewage as well from diffuse sources and the extended dry period in 2007.