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

Abstract

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 (ΣS2−, ΣS2− = 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+, ΣS2−, 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 ΣS2−, but not in water columns with high Fe2+ and low ΣS2−, or low Fe2+ and ΣS2−. During the formation of black bloom, Fe2+ increases quickly as DO decreases but starts to decrease before the outbreak of black bloom. ΣS2− concentrations only increase sharply 12 h before the outbreak. Both Fe2+ and ΣS2−, affected by oxic and redox conditions, respectively, contribute to the formation of black bloom. However, ΣS2− is confirmed to be the limiting factor directly controlling the outbreak of the black bloom.