Factors related to aggravated (cyanobacteria) bloom following sediment dredging in an eutrophic shallow lake.

In recent years, blooms have been widely found worldwide. Topics dealing with the mitigation of bloom is of great importance for toxins produced could threaten public health. The paper first investigated dynamics over three years following sediment dredging in a shallow eutrophic Lake Dongqian (China). Based on gene copies, bloom formed with average density of 1.30 × 10 cells/L on July 2009. One year later after sediment dredging, cell density decreased below 1.17 × 10 cells/L or under detected limits during summer days on 2010. While two years later, the bloom period was returned with markedly increased cell density reaching up to 4.15 × 10 cells/L on October 2011, and the maximum peak density was shown at 20.3 °C that was much lower than reported optimal growth temperature. Inferred from Spearman correlation analysis, linear regression showed density was significant and positive with pH and SD, whereas they were significant and negative with TP and DO. Multiple regression analysis further demonstrated that TN, TP, SRP, pH and DO provided the best model and explained 53.1% of the variance in dynamics. The approaches managing nutrients reduction might not control bloom as extremely low TN (avg. 0.18 mg/L) and TP concentrations (avg. 0.05 mg/L) resulted in the highest cell density after sediment dredging.