Effect Of Aquatic Ecosystem Restoration Engineering On The Phosphorus Content In Surface Sediments Of Lake Taihu, China

The aquatic ecosystem is undergoing changes with the implement of Meiliang Bay aquatic ecosystem restoration engineering. In order to evaluate the effect of the aquatic ecosystem restoration engineering on the surface sediments, we carried out three aspects of experiment: 1) Effect of macrophytes restoration on the nutrient content in surface sediments of Lake Taihu, China. 2) Effect of wave dissipation engineering on sediments resuspension and nutrient release in Lake Taihu. 3) Simulated study on concentration changes of different forms of phosphorus caused by wind-wave disturbance in shallow lake.The whole-year investigation results showed that TP concentration, TN concentration were declining with time and LOI of sediments had a little change. Concentrations of chlorophyll a(chl a) in the overlying water showed similar seasonal change with TP, TN concentration reached the highest value in summer and the lowest in spring. The decline of the particulate nutrients in the water and the uptake of aquatic macrophytes might decrease the nutrient load of surface sediments. All of these results indicated that the aquatic ecological restoration engineering in Lake Taihu is of significance in reducing the internal pollution of the lake.Resuspension flux in and out of the engineering area showed that wave dissipation engineering could weak wind-wave disturbance to sediments, restrain sediments resuspension and lower nutrient resuspension flux. They also stated that organic matter in suspended solid was reducing with the increasing of suspended solid. Accoringly, phosphorus in per suspended solid would reduce too. Dissolved phosphorus did not increase in the observation, though sustained wind-wave disturbance might bring much dissolved phosphorus of the sediments into overlying water. Suspended solids could absorb dissolved phosphorus in the water. As a result, dissolved phosphorus will not increase dramatically with drastic sediments resuspension, even decrease.The simulated disturbance experiment results showed that at the beginning of disturbance, suspended solids (SS), total phosphorus (TP), particle phosphorus (PP) and dissolved total phosphorus (DTP) in water increased remarkably. SS, TP and PP would reach their maximum value when the disturbance lasted half a day. SS, TP and PP needed at least 10 days to drop to undisturbed level. During the disturbance period, DTP kept high value, but it dropped immediately when the disturbance stopped, while SRP had no big change during the whole process. Dissolved phosphorus in anaerobic sediments would release easily at the beginning of disturbance, then they sunk to the bottom of water with SS for the increasing of oxygen in water. During the period of disturbance and a day after calm wind, the particle size of SS decreased constantly, which means SS would be able to adsorb more and more phosphorus. Long time after calm wind, particle size became bigger and bigger for flocculation and SS brought by disturbance settled almost completely. The study states that increasing of oxygen in water, percent growth of organic matter in SS and decreasing of particle size with the disturbance lasting can enhance adsorption ability of SS to phosphorus, though wind-wave disturbance can bring much PP and DTP into water, which can be used directly or indirectly by algae. Active phosphorus concentration in water has no big change as a result of the two processes interaction.