Dados da Tese de Doutorado
Author: Elisabete Lourdes do Nascimento
Títle: Environmental factors regulating the cyanobacteria dynamics in the Samuel’s reservoir hydreletric powerplant, Rondônia (Western Amazon,Brazil).
Year: 2012. Full text (in Portuguese)
Abstract
Cyanobacteria are photosynthetic prokaryotes with extensive development in eutrophic environments, a phenomenon called bloom. Besides the social and environmental damage caused by blooms, these may become a public health problem due to some cyanobacteria be able to synthesize cyanotoxins. In a previous study conducted in the Samuel’s hydroelectric powerplant reservoir (Rondônia), located in Jamari sub-basin,an increase was observed in the density of Microcystis sp (Cyanobacteria) with the increase of flow. Therefore, this study aimed to evaluate, through field and laboratory studies, environmental factors related to the cyanobacteria and cyanotoxins dynamics in this reservoir. Data are presented in three chapters. Chapter I deals with environmental variables and their correlation with phytoplankton, from data obtained over a hydrological cycle (Feb/2007-Feb/2008). The dominance of cyanobacteria occurred in March (Aphanocapsa holsatica and Microcystis panniformes) and May (Merismopedia tenuissima), however in most of the studied period the Chlorophycea were dominant. The Cyanobacteria dominance occurred in the rainy months, which showed nutrients in high concentrations. In February the Microcystins concentrations were detected in raw water above the maximum permissible value recommended by the national legislation 518/2004/MS (1μg.L-1). Knowing that the left bank of the reservoir has large areas deforested for cattle ranching and the bare soil contributes to the allochthonous input of nutrients, Chapter II presents data of an experiment in microcosms whose objective was to determine the effects of nutrient enrichment in phytoplankton community, specifically investigating the growth of cyanobacteria. Only when the P treatment was added alone (250 μg.L-1), Dolichospermum solitariumit was observed dominance of at 24th and 35th day of the experiment. In this period have limited the DIN concentrations were low (150 μ.L-1)and that might have limited growing of other phytoplankton species and favored D. solitarium, since this one is able to fix atmospheric nitrogen. Chapter III describes the physiological response of M. panniformis isolatedfrom reservoir, when growing under different iron concentrations (0, 23 e 223 μg.L-1/controle) for 8 days. After 7 days of Fe complete deprivation resulted in slower growth and reduced chlorophyll synthesis starting on the 4th day. Higher concentrations of microcystin-LR were observed in 23 μg.L-1 Fe and control. The information generated contributed to elucidate the environmental variables related to cyanobacteria development in the reservoir and the concentration of microcystins, among which stand out the N and P whose input to reservoir may increase due to the form of land, and Fe, the characteristic element of the region geology.
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