PhD candidate, Griffith University/Australian Rivers iNSTITUTE
I developed my interests in cyanobacteria since 2007, when the severe Microcystis blooms caused the water crisis in Lake Taihu (China). I worked on Microcystis and continued to study the role of abiotic and biotic factors in promoting its growth, bloom formation and spatio-temporal structure in the field afterwards. My PhD topic focuses on a poorly studied topic: how physical factors, i.e., light, temperature and water turbulence, affect the bloom formation, and why the bloom condition varies with reservoirs based in Southeast Queensland Australia. I am trying to predict the blooms via phytoplankton dynamic models and one-dimensional hydrodynamics models.
Abstract: Field investigations in Lake Taihu (China) were carried out from 1 June 2010 to 15 November 2010 in order to analyze environmental factors related to the succession of Microcystis wesenbergii and M. aeruginosa. M. wesenbergii dominated from the middle of July to the middle of September, and then, M. aeruginosa dominated subsequently. Cell density of M. wesenbergii was high when water temperature was higher than 28 °C, and total dissolved nitrogen:total dissolved phosphorus (TDN:TDP) ratio was below 7 (by weight), but low temperature (lower than 23 °C) was favorable to high cell density of M. aeruginosa. Cell density of M. wesenbergii was low when concentration of total dissolved phosphorus (TDP) was lower than 0.05 mg L−1 and iron concentration was below 0.4 mg L−1; however, cell density of M. aeruginosa was high under these conditions. Our results suggested that temperature and nitrogen:phosphorus (N:P) ratio did not affect the succession of M. wesenbergii and M. aeruginosa. Environmental factors did not explain all of the variation (less than 50 %) and suggested that colonial morphological changes induced by mucilage solubilization should be considered.
Pub.: 11 Apr '16, Pinned: 28 Jul '17
Abstract: The buoyancy of Microcystis colonies is a principal factor determining blooms occurrence but the knowledge of seasonal variation in buoyancy is quite poor because of challenge in analysis method. In this study, a method based on the Stokes' Law after researching on the effects of shapes on settling velocity of Microcystis colonies, whose gas vesicles were collapsed, to accurately measure density was established. The method was used in Lake Taihu. From January to May, mean density of Microcystis colonies decreased from 995 kg m(-3) to 978 kg m(-3) and then increased to 992 kg m(-3) in December. The density of colonies in different Microcystis species was in the order M. wesenbergii > M. aeruginosa > M. ichthyoblabe. For all the Microcystis species, the density of colonies with gas vasicles increased significantly along with the increase of colony size. Our results suggested that the main driving factor of Microcystis blooms formation in Lake Taihu was low density for M. ichthyoblabe from May to July but was large colony size for M. wesenbergii and M. aeruginosa from August to October.
Pub.: 15 Nov '16, Pinned: 28 Jul '17
Abstract: Fortnightly investigations at 12 sampling sites in Meiliang Bay and Gonghu Bay of Lake Taihu (China) were carried out from June to early November 2010. The relationship between abiotic factors and cell density of different Microcystis species was analyzed using the interval maxima regression (IMR) to determine the optimum temperature and nutrient concentrations for growth of different Microcystis species. Our results showed that cell density of all the Microcystis species increased along with the increase of water temperature, but Microcystis aeruginosa adapted to a wide range of temperatures. The optimum total dissolved nitrogen concentrations for M. aeruginosa, Microcystis wesenbergii, Microcystis ichthyoblabe, and unidentified Microcystis were 3.7, 2.0, 2.4, and 1.9 mg L(-1), respectively. The optimum total dissolved phosphorus concentrations for different species were M. wesenbergii (0.27 mg L(-1)) > M. aeruginosa (0.1 mg L(-1)) > M. ichthyoblabe (0.06 mg L(-1)) ≈ unidentified Microcystis, and the iron (Fe(3+)) concentrations were M. wesenbergii (0.73 mg L(-1)) > M. aeruginosa (0.42 mg L(-1)) > M. ichthyoblabe (0.35 mg L(-1)) > unidentified Microcystis (0.09 mg L(-1)). The above results suggest that if phosphorus concentration was reduced to 0.06 mg L(-1) or/and iron concentration was reduced to 0.35 mg L(-1) in Lake Taihu, the large colonial M. wesenbergii and M. aeruginosa would be replaced by small colonial M. ichthyoblabe and unidentified Microcystis. Thereafter, the intensity and frequency of the occurrence of Microcystis blooms would be reduced by changing Microcystis species composition.
Pub.: 05 Sep '15, Pinned: 28 Jul '17
Abstract: Publication date: February 2017 Source:Harmful Algae, Volume 62 Author(s): Man Xiao, Anusuya Willis, Michele A. Burford Microcystis aeruginosa and Cylindrospermopsis raciborskii are two cyanobacterial species that dominate freshwaters globally. Multiple strains of each species with different physiology occur, however, many studies have focused only on one or two strains, limiting our understanding of both strain variation and characterisation of the species. Therefore, in this study we examined the variation in growth and morphology of multiple isolates of both species, isolated from two adjacent Australian reservoirs. Four M. aeruginosa strains (=isolates) (one colony-forming, three single-celled morphology) and eight C. raciborskii isolates (five with straight trichomes, three with coiled trichomes) were cultured individually in a factorial designed experiment with four light intensities (L: 10, 30, 50 and 100μmol photons m−2 s−1) and two temperatures (T: 20 and 28°C). The specific growth rate (μ), cell volume, and final cell concentration was measured. The light attenuation coefficient (kj), a measure of self-shading, was calculated. The results showed that the intraspecific variation was greater than the interspecific variation. The μ of all isolates of M. aeruginosa and C. raciborskii ranged from 0.16 to 0.55d−1 and 0.15 to 0.70d−1, respectively. However, at a specific light and temperature the mean μ of all M. aeruginosa isolates and C. raciborskii isolates were similar. At the species level, M. aeruginosa had higher growth rates at higher light intensity but lower temperature (L100T20), while straight C. raciborskii had higher growth rates at lower light intensity but higher temperature (L50T28), and coiled C. raciborskii had higher growth rates at higher light intensity and higher temperature (L100T28). The final cell concentrations of M. aeruginosa were higher than C. raciborskii. However, C. raciborskii isolates had greater variation in μ, kj and cell volume than M. aeruginosa. kj varied with light and temperature, and decreased with surface-to-volume ratio within each species. kj was lower for M. aeruginosa compared to C. raciborskii as expected based on cell size, but interestingly, C. raciborskii coiled isolates had lower kj than the straight isolates suggesting lower effect of self-shading. This study highlights the extent of strain variation to environmental conditions and to species variability.
Pub.: 08 Jan '17, Pinned: 28 Jul '17