School of Civil, Environmental and Mining Engineering

Postgraduate research

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Current and completed research by our postgraduate students.

Contact

Som Cit Si Nang

Phone: (+61 8) 6488 1687


Start date

Nov 2007

Submission date

Jun 2011

Links

Curriculum vitae

Som Cit Si Nang CV
[doc, 2,143.70 kb]
Updated 15 Jun 2011

Som Cit Si Nang

Som Cit Si Nang profile photo

Thesis

Spatial and Temporal Dynamics of Cyanobacterial Toxins in Freshwater Systems: Implications for Water Quality Management

Summary

Excessive growth of cyanobacterial biomass, commonly known as cyanobacterial blooms, appear to be increasing in magnitude and frequency worldwide, thus posing an additional 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 manage the occurrence and assess public health risks associated with cyanobacterial blooms due to difficulty in predicting the level of cyanobacterial biomass and microcystin concentrations. The effectiveness of strategies currently used in the management and public health risk assessment depend upon the understanding of the dynamics of cyanobacteria and microcystin under natural conditions. This research aims to: i) assess the relationship between cyanobacterial biomass and microcystin concentration, which is the indirect microcystin risk assessment traditionally used by water authorities; ii) explore the environmental drivers of the dynamics of cyanobacterial dominance and microcystin production 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 production.

The results revealed that cyanobacterial and microcystin spatiotemporal dynamics affect the biomass-toxin relationship and posing a significant challenge in the indirect microcystin risk assessment. 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. The divergence in the biomass-toxin correlation suggests a direct effect of the environmental factors on the dynamics of cyanobacteria and microcystin production. Environmental factors, particularly nutrient concentrations are significantly correlated to the spatiotemporal dynamics of cyanobacteria and microcystin production. Low phosphorus and iron concentrations in the water column trigger the dominance of cyanobacterial biomass in the phytoplankton community. In contrast, high phosphorus and iron concentrations in the water column trigger high microcystin production. Different nutrient factors explained the succession of different cyanobacterial genera at the cyanobacterial community level. Nevertheless, the correlations between the cyanobacterial and microcystin dynamics and environmental factors are site-specific. In addition to nutrients, changes in the structure of phytoplankton community are also significantly correlated to the dynamics of microcystin production. Under high nutrient concentrations, cyanobacteria may not dominate the phytoplankton community. Higher microcystin production associated with increased nutrient concentrations and the dominance of other phytoplankton groups in the systems supports the hypothesis of allelopathic interaction in cyanobacteria.

The results presented in this thesis will provide a new basis for the improvement of the assessment strategies used to determine the risk of the presence of cyanobacterial blooms and their associated toxins in water systems to humans and the environment.

Why my research is important

With regards to the serious harm of toxic cyanobacterial blooms to the water safety, a better understanding of the ecological conditions leading to the intensification of cyanobacterial blooms and their toxicity in water bodies is needed. More information on the environmental triggers of the excessive cyanobacterial growth and their toxins production will add to the ability to predict and manage the increasing threat of toxic cyanobacterial bloom in water bodies.

Funding

  • Scholarship: Ministry of Higher Education, Malaysia
  • Research funding: ARC/ Water Corporation Linkage Project

Satellite image (A) and photograph (B) of the excessive cyanobacterial growth in Yangebup Lake, South West Australia (source of satellite imageof photograph: Nang, S.C.S., 2011).
 

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