The Limiting Factor to the Outbreak of Lake Black Bloom: Roles of Ferrous Iron and Sulfide Ions

Algae-induced black bloom, a kind of black water phenomenon in some severe eutrophic lake areas, is characterized by a black color and offensive odor and is one of the most serious environmental problems in certain eutrophic shallow freshwater lakes in China. Ferrous iron (Fe2+), soluble inorganic sulfides (sigma S2-, sigma S2-=S2-+HS-+H2S), and dissolved oxygen (DO) in the overlying water are presumed to be directly related to the formation of black blooms. In this study, the algae-induced black bloom in Lake Taihu, China, is simulated in the laboratory by using a large-scale lake process simulation apparatus. Changes in the characteristics of Fe2+, sigma S2-, DO, pH, and oxidation reduction potential (ORP) are investigated during the entire black bloom formation period. Results show that black blooms occurr in water columns with high Fe2+ and sigma S2-, but not in water columns with high Fe2+ and low sigma S2-, or low Fe2+ and sigma S2-. During the formation of black bloom, Fe2+ increases quickly as DO decreases but starts to decrease before the outbreak of black bloom. sigma S2- concentrations only increase sharply 12h before the outbreak. Both Fe2+ and sigma S2-, affected by oxic and redox conditions, respectively, contribute to the formation of black bloom. However, sigma S2- is confirmed to be the limiting factor directly controlling the outbreak of the black bloom.