Analysis of phytoplankton presence in an integral basin of the Integration Project of Sao Francisco River, semiarid region, Northeast Brazil

Phytoplankton taxonomic studies are important tools to analyze the quality of water, allowing the monitoring of waters used for multiple purposes. Thus, this work aimed at studying the formation and distribution of phytoplankton in stretches of the Piranhas-Acu River Basin, in the semiarid region of Northeastern Brazil, from 2010 to 2011, with 13 sampling points in river and reservoirs. We identified 81 infrageneric taxa, distributed into 9 classes: Cyanophyceae, Chlorophyceae, Bacillariophyceae, Trebouxiophyceae, Euglenophyceae, Coscinodiscophyceae, Zygnematophyceae, Mediophyceae, and Klebsormidiophyceae. The Chlorophyta and Cyanophyta divisions were the most representative, with 30 (37%) and 24 (30%) taxa, respectively. However, the cyanobacteria were more seen throughout the study period. In some sampling points, they had limits above 20.000 cells/mL, requiring weekly monitoring as provided by Decree 2914 from December 12, 2011, of the Brazilian Ministry of Health. The species with high abundance are those producing toxins, represented by Cylindrospermopsis raciborskii, Pseudanabaena limnetic, Microcystis sp. Dolichospermum sp., and Oscillatoria sp. The data indicate a potential health risk to the population served by these waters.