Response of internal phosphorus loading from dredged and inactivated sediment under repeated resuspension in a eutrophic shallow lake

In this study, a laboratory sediment resuspension simulation system (RSS) was used to investigate the effect of wind -induced (5.3 and 8.7 m/s) repeated sediment resuspension on internal phosphorus (P) in sediment treated by dredging and La-modified clay (LMC) based inactivation in a shallow lake. The results indicated that the dredged sediment had a better capability to resist repeated wind disturbance than the LMC-inactivated sediment. The concentration of suspended solids (SS) in the inactivated treatment (70.7 mg/L) was 1.7 times that in the dredged treatment (41.7 mg/L) under moderate wind disturbance, and was similar for the two treatments under strong wind disturbance. Nev-ertheless, dredging performed better than inactivation in reducing 44 % total phosphorus (TP) in overlying water (43 % reduction by inactivation) and 31 % mobile Pin sediment (27 % reduction by inactivation) under moderate wind disturbance (p < 0.01) compared with control treatment. Inactivation performed better in reducing 57 % P in porewater (52 % reduction by dredging) and 81 % P flux (13 % reduction by dredging) (p < 0.01) compared with con-trol treatment. Surprisingly, under strong wind disturbance, LMC inactivation could still reduce 18 % P in porewater and 75 % P flux (p < 0.01), whereas dredging increased 25 % Pin porewater and 13 % P flux compared with control treatment (p < 0.01). LMC inactivation can increase the sediment P adsorption capacity and decrease the equilibrium P concentration (EPC0) when compared with control treatment. The contrasting control effects of the two methods were probably due to the different P buffer mechanisms for the two treated sediment. The wind disturbance-induced sedi-ment P release was controlled by the inactivation of Fe and co-inactivation of Fe and La at the surface of dredged and LMC-inactivated sediments, respectively. The results of this study indicated inactivation can be a better method to con-trol sediment internal P loading with repeated strong wind disturbances in eutrophic lakes.

Automated summary

In this study, the effect of wind-induced sediment resuspension on internal phosphorus in sediment treated by dredging and La-modified clay (LMC) based inactivation was investigated using a laboratory sediment resuspension simulation system (RSS). The results showed that dredged sediment had a better resistance to repeated wind disturbance compared to LMC-inactivated sediment. Both methods were effective in reducing phosphorus in different compartments of the lake, but their performances varied depending on the wind disturbance level. Inactivation was found to be a better method for controlling sediment internal phosphorus loading with repeated strong wind disturbances in eutrophic lakes.