Investigation on the Growth Mechanism of the Toxic Cyanobacterium (Lyngbya majuscula) in Moreton Bay, Queensland, Austraria

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We have investigated on the behavior of iron in coastal waters and iron uptake mechanism of toxic cyanobacterium, Lyngba majuscula, and developed a numerical model to predict the dynamics of bioavailable iron in coastal waters. Follows are major outcomes from this study.1.Laboratory experiment and field work were conducted to understand forms of iron in coastal water and behavior of humic iron complex such as equilibrium and coagulation. It was found that ferric iron complexed by humic substances (HS) is predominant iron species in river water, however, 90 % of the complex dissociates in coastal water due to the competition with divalent seawater cations (i.e.,Ca^<2+> and Mg^<2+>). Chromatography analysis revealed that coagulation was least for HS which has low molecular weight and hydrophobicity, indicating that HS having these properties are the most important contributor to transport dissolved iron from river to coastal waters.2.The numerical model to predict behavior of humic iron … More complex was developed, considering the physicochemical behavior of humic iron complex such as equilibrium, coagulation and diffusion. The equilibrium model was developed on the basis of Debye-Huckel theory that is able to take account of the potential energy of iron around the surface of HS. The coagulation model was developed by involving hydrophobolic interaction, a strong attractive force working among HS molecules, into the well established DLVO theory. The equilibrium and coagulation model was then combined with diffusion model (Navier-Stokes and diffusion equations), allowing us to numerically calculate the spatial and temporal distributions of humic iron complex in coastal water.3.The kinetics of bioavailable iron production via superoxide-mediated reactions was investigated to develop a model for the iron uptake by L. majuscula. Although the rate of superoxide-mediated production of bioavailable Fe(II) (i.e., bioavailability of iron) varies due to the different origin of humic iron complex, the humic iron complex with higher content of acid functional groups generally shows lower bioavailability. By determining the kinetic rate constants involved in Fe(II) production, reaction scheme in terms of iron uptake was developed. The model calculated that the strong humic iron complex produces Fe(II) via non-dissociative reduction pathway in which the Fe(III) complexed by HS is reduced by superoxide prior to the complex dissociation. The results indicated that management and environment of catchments such as land use and vegetation (i.e.,origin of HS) significantly affect the bioavailability of iron in coastal waters..In summary, the numerical model which involves the equilibrium, coagulation, diffusion and bioavailability of humic iron complex was developed in this work. The model allows us to comprehensively assess and predict the process of iron uptake by L.majuscula in coastal waters. Less