Immobilization and Release Behavior of Phosphorus on Phoslock-Inactivated Sediment under Conditions Simulating the...

Phosphorus-inactivating agents (PIAs) have increasingly been applied and extensively investigated to control internal phosphorus loading in lakes. However, little is known about the behavior of PIA-amended sediment in terms of phosphorus immobilization and release when the sediment is resuspended in the photic layer, whose environment differs from the lake bed. Lanthanum-modified bentonite (LMB) is a popular PIA product. In this study, the 33 day core incubation experiment under dark conditions showed that capping sediment with LMB efficiently decreased the concentration of total phosphorus, total dissolved phosphorus, and dissolved inorganic phosphorus (DIP) by 90, 87, and 99%, respectively. Resuspension into overlying water under light conditions at high pH, high dissolved organic carbon, and in the presence of algae significantly impedes the performance of LMB. However, the adoption of a higher LMB dose improved the performance, including a reduction in the phosphorus level and control of algal growth. The dynamics of the phosphorus migration when the LMB-inactivated sediment was resuspended into the photic zone mainly involves the release of DIP from the sediment and the uptake of DIP by algae and LMB. In conclusion, a higher dose is needed in the PIA (particularly Phoslock) application in shallow productive lakes where sediment resuspension occurs frequently.