[Release of colloidal N and P from sediment of lake caused by continuing hydrodynamic disturbance]

The course of continuing hydrodynamic disturbance and succeeding long time settlement of lake water was simulated to study the release of nitrogen (N) and phosphorus (P) from lake sediment. It was showed in the experiment that the hydrodynamic disturbance caused abundant release of particulate and colloidal phosphorus and nitrogen. The concentration of total nitrogen (TN) and total phosphorus (TP) in water reached the highest values of 2.106 mg/L and 0.272 mg/L, respectively, when the water was disturbed for 0.5 d, and the concentration of colloidal nitrogen (CN) and colloidal phosphorus (CP) in water reached the highest values of 0.452 mg/L and 0.052 mg/L, respectively, when the water was disturbed for 1 day. Then, the concentration of TN, TP, CN and CP turned to decrease despite the continuing disturbance, for the particles and colloid deposited exceeded that suspended. During the settling phase after disturbance, the bigger suspended particles deposited quickly while the tiny colloid deposited much slower, and the concentration of CN and CP did not decrease until the water was settled for 1 day. The concentration of ultra-filtrated dissolved nitrogen (UDN) and ultra-filtrated dissolved phosphorus (UDP) increased much more in the settling phase than in the disturbing phase. It can be drawn that the adsorption of colloid limited the increase of dissolved N and P in lake water in the disturbing phase and prolonged the time of suspended N and P stayed in water. And the N and P adsorbed by colloid could also be released into water in the settling phase after disturbance, which delayed the elimination of nutrition and improvement of water quality.