A Preliminary Study On The Available Iron Abundance In Relation To The Formation Of Blue Algae Bloom In Taihu Lake

Lake water eutrophication in China has become one of the most serious water-pollution problems. In recent years, the frequent blue algae bloom during summer season in the eutrophication Taihu, the third largest lake in China has been disrupting the water supply for millions of people. The blue algae bloom in Taihu has not been effectively controlled as the mechanism for the formation of the blue algae bloom has not been fully understood.Iron is an essential element for all the living organisms, and has been proven to be a limit factor for algae growth in some ocean waters and fresh waters. In this study, we investigated the background level of iron in Taihu waters and the response of the algae to iron limitation and addition in a pot incubation experiment using sampled Taihu waters in a glass house. The results are summarized as follows:1). The Taihu Lake water was high in the dissolved Fe level-2024ppb, indicating that Taihu Lake had a large size of Fe pool for phytoplankton growth.2). The blue algae growth was significantly (P=0.05) inhibited as the water pH elevated in the glasshouse pot incubation experiment. The blue algae populations (cells.mL^-1) decreased with the pH increasing in the treatments of pH 10, 11, 11.5 and 12. Addition of 3mg.L^-1 EDTA-Fe after the water pH was adjusted to 12 promoted significantly the algae growth in comparison with the pH 12 treatment as the algae cell populations were 13386 and 5023cells.mL^-1, respectively in the Fe addition treatment and the pH 12 treatment.3). The blue algae growth was also significantly (P=0.05) inhibited by addition of activated carbon, especially when the activated carbon was treated with Ca(OH)₂. In the last day of the incubation experiment, the cell number per mL of the water was about 7170cells.mL^-1 when the water was added with 3g.L^-1 Ca(OH)₂-treated activated carbon while that in the control was 21934cells.mL^-1.4). The microscopy analysis results showed that the dominant algae species of the water sample of Taihu Lake was Gloeocapsa sp. In the water sample which was added with 3g.L^-1 activated carbon, the dominant algae specie had changed from Gloeocapsa sp to A. acicularis.5). The content of Fe²⁺ of the water sample was determined in the eighth day and the last day of the incubation experiment. The pH 12 treatment had the lowest content of Fe²⁺, and the water sample treated with 3g.L^-1 Ca(OH)₂-treated activated carbon had the second lowest Fe²⁺ content.These preliminary results indicated that the formation of the blue algae bloom in Taihu Lake was associated with the high available Fe abundance.