Cyanobacterial diversity in water sources of the Sorocaba river basin, with emphasis on the Itupararanga and Ipaneminha dams, São Paulo state, southeastern Brazil

Abstract

The Ituparanga and Ipaneminha rivers supply 85% of the population from the region of Sorocaba municipality (São Paulo state). These rivers were monitored from November 2007 to January 2009 in five sampling points, by analyzing cyanobacterial diversity therein as well as physical and chemical variables, following the procedures and quality criteria determined by CONAMA Resolution no. 357 and by Ordinance no. 2914 of the Brazilian Health Ministry. Our results revealed the occurrence of cyanobacteria in most points, with seasonal variation. Cyanobacterial richness was associated with increased nitrogen concentration resulting from point (sewage) and diffuse (agriculture) pollution sources. Cell density was not correlated to the increase in phosphorus content. The high occurrence of Dolichospermum solitarium, Aphanizomenon gracile, Cylindrospermopsis raciborskii and Microcystis aeruginosa, all of which are species that commonly occur in eutrophic environments, represents an issue for water resource managers, as it reveals a water quality impairment that reflects the occurrence of an environmental imbalance in the studied ecosystem mostly caused by the aforementioned human activities.