UPSI Digital Repository (UDRep)
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UPSI Digital Repository (UDRep)
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| Abstract : Perpustakaan Tuanku Bainun |
| 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. In relation to the environmental drivers of the dynamics of cyanobacterial dominance and_ microcystin concentration, the results revealed the significant role of phosphorus and iron_ concentrations in the water column. Low phosphorus and iron concentrations in the water column__ trigger_ the dominance_ of cyanobacterial biomass_ in the phytoplankton community. Specifically_ with regard to bloom toxicity, high phosphorus and iron concentrations in the water column trigger_ high microcystin concentration. Furthermore,_ different concentrations of phosphorus,_ nitrogen__ and_ iron_ species explained the succession of different cyanobacterial genera at the_ cyanobacterial community level. Nevertheless, the correlations between the dynamics of_ cyanobacterial dominance and microcystin concentration and environmental factors are site-specific._ This might potentially be related to the effect of spatial heterogeneity of the local nutrient_ concentrations and cyanobacterial community present in the systems. In addition to nutrients, changes in the structure of phytoplankton community are also_ significantly correlated to the dynamics of microcystin concentration. Under high nutrient_ concentrations, other phytoplankton groups are capable of growing faster and gain dominance over_ cyanobacteria. However, this study shows that under this scenario, cyanobacteria produce more_ toxins. This supports the hypothesis of allelopathic interaction in cyanobacteria. The results presented in this thesis will improve the fundamental understanding of the dynamics of_ toxic cyanobacterial blooms. Additionally, these results can be used to supplement the existing_ strategies for the prevention of cyanobacterial blooms and assessment_ of risk associated_ with_ cyanobacterial_ toxins to humans and_ the environment. _ |
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