Florações de cianobactérias em um reservatório urbano tropical submetido a medidas de restauração: dinâmica da comunidade e cianotoxinas

Abstract

Eutrophication of urban water bodies is a significant environmental problem, particularly in tropical regions, where the combination of high nutrient availability, elevated temperatures, and intense solar radiation promotes the proliferation of potentially toxic cyanobacterial blooms. This thesis investigates the long-term effect of using Phoslock®, a lanthanum-modified bentonite clay, as a phosphorus control strategy to mitigate cyanobacterial blooms in a hypereutrophic urban reservoir (Pampulha Reservoir, Belo Horizonte, MG). The study included both field monitoring and laboratory experiments to evaluate the effectiveness of Phoslock in reducing bioavailable phosphorus and its effects on phytoplankton community dynamics and cyanobacterial toxin profiles. Chapter 1 presents a seven-year field study, including monitoring before and during Phoslock treatment, showing that although Phoslock contributed to phosphorus reduction in some periods, the persistence of external nutrient loads compromised its effectiveness. A temporary reduction in cyanobacterial blooms and an increase in phytoplankton diversity were observed; however, the treatment effect was limited by constant external interferences, highlighting the importance of integrated control to achieve lasting recovery. Chapter 2 includes laboratory experiments with different strains of cyanobacteria and microalgae exposed to Phoslock to assess their growth responses and physiological changes, including intracellular chlorophyll content and cyanobacterial toxin production. Laboratory results confirmed that Phoslock reduces phosphorus availability and may inhibit the growth of cyanobacteria and microalgae, although responses vary between species and strains. The experimental study contributed to understanding how specific species respond to phosphorus control, allowing an assessment of possible implications for field management. Chapter 3 reviews the challenges and strategies for restoring eutrophic urban lakes in the context of the Anthropocene. Each technique is discussed in terms of its advantages and limitations, with emphasis on the effects of climate change, which may intensify eutrophication and complicate cyanobacterial bloom control. The results of this work may contribute to the management of eutrophic urban aquatic ecosystems and underscore the importance of integrated public policies for sustainable eutrophication control. It is recommended that future recovery programs prioritize the control of external nutrient sources and adopt combined strategies to improve water quality in the long term. This study provides a scientific basis to guide management decisions and public policies, especially for the restoration of tropical reservoirs.