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

我们研究了沿海水域铁的行为和有毒蓝藻（Lyngba majuscula）对铁的吸收机制，并建立了预测沿海水域生物可利用铁动态的数值模型。以下是本研究的主要结果：通过室内实验和实地考察，了解了近岸水体中铁的形态和腐殖质铁络合物的平衡、混凝等行为。研究发现，河流水体中以腐殖质（HS）络合铁为主，但沿海水体中90%的络合铁由于与二价海水阳离子（Ca^<2+>和Mg^<2+>）的竞争而游离。色谱分析结果表明，具有低分子量和疏水性的HS的混凝作用最小，表明具有这些特性的HS是将溶解铁从河流输送到沿海水域的最重要因素。考虑到腐殖质铁络合物的平衡、混凝和扩散等物理化学行为，建立了腐殖质铁络合物性能预测的数值模型。平衡模型是在Debye-Huckel理论的基础上建立的，该理论能够考虑HS表面周围铁的势能。混凝模型是通过将HS分子间的强引力——疏水相互作用纳入到完善的DLVO理论中来建立的。将平衡和混凝模型与扩散模型（Navier-Stokes方程和扩散方程）相结合，对近岸水体腐殖质铁络合物的时空分布进行了数值计算。研究了通过超氧化物介导反应产生生物可利用铁的动力学，建立了L. majuscula铁摄取模型。虽然腐殖质铁络合物的来源不同，其超氧化物介导产生生物可利用性铁（即铁的生物利用度）的速率也不同，但酸性官能团含量较高的腐殖质铁络合物的生物利用度一般较低。通过确定铁（II）生成的动力学速率常数，制定了铁摄取的反应方案。该模型计算出强腐殖质铁配合物通过非解离还原途径产生Fe(II)，其中HS配合的Fe（III）在配合物解离之前被超氧化物还原。结果表明，流域的管理和环境，如土地利用和植被（即HS的来源）对沿海水域铁的生物利用度有显著影响。综上所述，本文建立了腐殖质铁络合物平衡、混凝、扩散和生物利用度的数值模型。该模型使我们能够综合评价和预测马氏l.a majuscula在沿海水域的铁吸收过程。少

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