Simulation of black bloom in Moon Bay of Lake Taihu and physical and chemical responses of water and sediment

Black bloom in Lake Taihu has become a matter of considerable concern in recent years. However, it is difficult to monitor the bloom timely and effectively, because the bloom may move from place to place and from time to time. The algae-originated black bloom in the Moon Bay of Lake Taihu was reproduced under indoor laboratory conditions in this study. The experiment used a Y-shape apparatus to simulate the sediment resuspension process. Quantitative changes in primary parameters both in overlying water and surface sediments were monitored during black bloom. The experimental data were analyzed. The result shows that the overlying water has undergone an oxic-hypoxic-anoxic period during the bloom. The dissolved oxygen (DO) level decreases from >6 mg/L at the beginning of the experiment to <0.5 mg/L after the black bloom. The water continues to darken until turned into black accompanying with a sudden burst of black bloom. The nutrient concentration in overlying water also increases steadily, which causes a heavy nitrogen and phosphorous pollution. Reduction of ferric iron (Fe(Ⅲ)) to ferrous iron (Fe(Ⅱ)) in surface sediments is greatly affected by the redox environment of water bloom, which creates a reducing environment (Fe(Ⅲ)/ Fe(Ⅱ) < 1) on the surface. At the same time, a sharp increase in acid volatile sulfides (AVS) in surface sediments is observable, and the maximum value of AVS (135.80 μmol/g) is found on the surface.