Mitigation of CyanoHABs Using Phoslock^® to Reduce Water Column Phosphorus and Nutrient Release from Sediment

Cyanobacterial blooms can be stimulated by excessive phosphorus (P) input, especially when diazotrophs are the dominant species. A series of mesocosm experiments were conducted in a lake dominated by a cyanobacteria bloom to study the effects of Phoslock^®, a phosphorus adsorbent. The results showed that the addition of Phoslock^® lowered the soluble reactive phosphate (SRP) concentrations in water due to efficient adsorption and mitigated the blooms. Once settled on the sediments, Phoslock^® serves as a barrier to reduce P diffusion from sediments into the overlying waters. In short-term (1 day) incubation experiments, Phoslock^® diminished or reversed SRP effluxes from bottom sediments. At the same time, the upward movement of the oxic-anoxic interface through the sediment column slightly enhanced NH₄⁺ release and depressed N₂ release, suggesting the inhibition of nitrification and denitrification. In a long-term (28 days) experiment, Phoslock^® hindered the P release, reduced the cyanobacterial abundance, and alleviated the bloom-driven enhancements in the pH and oxygen. These results suggest that, through suppression of internal nutrient effluxes, Phoslock^® can be used as an effective control technology to reduce cyanobacteria blooms common to many freshwater systems.