Mitigation of CyanoHABs Using Phoslock (R) 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 (R), a phosphorus adsorbent. The results showed that the addition of Phoslock (R) lowered the soluble reactive phosphate (SRP) concentrations in water due to efficient adsorption and mitigated the blooms. Once settled on the sediments, Phoslock (R) serves as a barrier to reduce P diffusion from sediments into the overlying waters. In short-term (1 day) incubation experiments, Phoslock (R) 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 N-2 release, suggesting the inhibition of nitrification and denitrification. In a long-term (28 days) experiment, Phoslock (R) 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 (R) can be used as an effective control technology to reduce cyanobacteria blooms common to many freshwater systems.