Determination of iron speciation in lake and its effects through iron availability on algal blooming

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Analytical methods were developed to determine the concentration of total dissolved iron and its chemical speciation in freshwater using cathodic stripping voltammetry (CSV) with 1-nitroso-2-naphthol (NN) at pH 8.1.The horizontal distribution and temporal variation of dissolved iron and its chemical speciation in Lake Kasumigaura and its inflowing rivers were investigated. Concentrations of dissolved iron and its organic ligands clearly decreased as lake water flowed from the river entry points toward the center of the lake, indicating their riverine origin. The fraction of iron occurring in organic complexes tended to increase with the water -flow. Most of the dissolved iron was present as organic complexes (882% 99.9%).Effects of iron complexation with DOM on algal growth in the eutrophic Lake Kasumigaura were assessed using 2 species of cyanobacteria, Microcystis aeruginosa and Planktothrix agardhii, by combining the algal growth potential (AGP) test and pretreatment of DOM decomposition by UV irradiation. Iron limited the 2 species, as did nitrogen and phosphorus in Lake Kasumigaura. Moreover, the growth of the 2 species was inhibited by iron complexation with DOM.The growth characteristics of two species of cyanobacteria, Microcystis aeruginosa and Planktothrix agardhii, in iron-limited continuous cultures were investigated. The relationships between dissolved iron concentration, cell quota of iron, and population growth rate were determined applying two equations, Monod's and Droop's equations. A kinetic model under iron limitation was developed based on the growth characteristics determined in this study. The model simulation suggested that Microcystis is a superior competitor under iron limitation.