Temporal analysis of Cyanobacteria and Trophic State Index in PCH Porto Franco (Tocantin's State, North Brazil) / Análise temporal de Cyanobacteria e Índice de Estado Trófico na PCH Porto Franco, Tocantins

Cyanobacteria are typical phytoplankton components and they have received attention from the scientific community due to develop blooms in eutrophic environments. The Trophic State Index (TSI) is diagnosis of water body’s condition due to trophic level. This work aimed to estimate water quality from PCH Porto Franco reservoir based on Cyanobacteria abundance and TSI. During the period of 2009 to 2014, 19 sampling were performed in four points in which were analyzed the phytoplankton community, phosphorus and chlorophyll a. Cyanobacteria were detected in all the monitored points and exhibit potentially toxic taxa, for instance, Cylindrospermopsis raciborski and Planktolyngbya limnetica. These organisms are substantially toxic and may provoke harm to human health and to the environment. The Cyanobacteria dominance is associated with mesotrophic to hypereutrophic conditions, which have occurred mainly in upstream barriers. The predominance of a lentic environment, underwater radiation availability and high nutrient concentration demonstrated by TSI are conditions that determine the significantly development of Cyanobacteria in this reservoir.