Spatial and temporal dynamics of cyanobacteria and microcystins in freshwater systems: implications for the management of water resources

[Truncated abstract] Excessive growth of cyanobacteria, commonly known as cyanobacterial blooms, appear to be increasing in magnitude and frequency worldwide, thus posing a serious threat to the safety and security of water resources. With the increasing global water stress, there is a need for effective management of cyanobacterial blooms in water bodies. So far, it has been a great challenge to mitigate and assess public health risks associated with cyanobacterial blooms due to difficulty in predicting the level of cyanobacterial biomass and microcystin concentrations in water bodies. Moreover, the effectiveness of the current bloom prevention and risk assessment strategies depend upon the understanding of the dynamics of cyanobacteria and microcystin under natural conditions. Thus, this research aims to: i) assess the variability of the relationship between cyanobacterial biomass and microcystin concentration, which is currently used to assess the risk to human and ecosystems health; ii) determine the environmental drivers of the dynamics of cyanobacterial dominance and microcystin concentration and assess site specificity of the environmental drivers; and iii) investigate how changes in the structure of phytoplankton community and cyanobacterial composition in response to nutrient concentration affect the dynamics of microcystin concentration. The results contained in this thesis revealed that the biomass-toxin relationship is a function of spatiotemporal patterns that affect cyanobacterial and microcystin dynamics. The correlation between the biomass and toxin is weak and site-specific, and large changes in total microcystin concentrations occur even at stable cyanobacterial biomass concentrations. This could pose a significant threat to the risk assessment associated with microcystin contamination in water bodies...