| Frequent outbreak of diatom bloom in eutrophicated rivers has increasing become a serious problems around world. While many studies have been focused on the blue-green algae bloom in lakes and reservoirs, knowledge on diatom bloom in rivers has lagged far behind. In order to understand the formation and the mechanism of diatom bloom in rivers, the present study investigated the dynamics of diatom bloom in Han-river, in particularly, the growth physiology of dominant diatom isolated from the river. The main results are summarized as follows:1. Seasonal dynamics of composition and the quantity of the phytoplankton in Han-jiang river was investigated and analyzed in relation to the change of physical-chemical factors in the river. It was showed that diatom was the main species in the river. The number of the dominant species in diatom bloom was increasing in the winter when the temperature was low.. The outbreak of diatom bloom in this river was closely related to the eutrophic of nitrate and phosphate, among others.2. In order to identify the dominant species in Han-jiang diatom, the micrograph and the valve picture under electron microscope of the dominant species was investigated. Morphologically, this species was similar to Cyclotella,Stephanodiscus. Based on 18S rRNA gene, the phylogenetic tree was established and this diatom was more close to Stephanodiscus.3. The dominant species was isolated and purified in laboratory. Its optimal culture conditions was also established. Thereby, effects of nitrate, phosphate, silicon, iron, temperature, illumination and initial pH on this diatom were investigated. It was found optimal growth for nitrate and phosphate was 40mg/L and 1.226mg/L, respectively. The growth was also enhanced in higher iron and silicon concentration. Besides, optimal temperature ranges from 15℃ to 20℃ ., and the illumination intensions from 5μEm-2s-1 to 50μEm-2s-1. Orthogonal test indicated that phosphate is the primary factor for growth,...
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