Study On Effect Of Submerged Plant On Sediment Suspension Under Different Flow Velocity Conditions

The stabilization of aquatic ecosystems was influenced by sediment resuspension,and the extent of the sediment resuspension was influenced by water velocity. Submerged plants have the ability to fix sediment resuspension and settlement. On one hand, the roots of submerged plant have the ability to fix sediment resuspension, on the other hand, the stems and leaves of submerged plants can reduce the water flow velocity so that the suspended particles in water can be resettled on the sediment or attached to leaf surface of submerged plant. Vallisneria natans, Potamogeton crispus, Hydrilla verticillata and Myriophyllum spicatum were used as the test material in imitative experimental device, aiming to reveal the action mechanism of submerged vegetation on sediment resuspension at different velocities. The results showed that:(1)when the water flow velocity were 0, 10, 20, 40, 60, 80 cm/s and the biomass of submerged plant was 1 kg/m2, both of the submerged plants could restrain the rising of water turbidity at different velocities. The Potamogeton crispus group had more apparent effect than Vallisneria natans group; at the same velocity, the underwater illumination of Potamogeton crispus group was stronger than Vallisneria natans group; both of the submerged plants could restrain the rising of Water nutrient at different velocities, the Potamogeton crispus group had apparent effect than Vallisneria natans group. For the turbidity, the inhibition rate was 57%~93%,47%~60%; For the total nitrogen,the inhibition rate was 31%~47.1%, 23%~35.8%; For the total phosphorus, the inhibition rate was 19.8%~43%,19.3%~30.6%. The control group, Potamogeton crispus group and Vallisneria natans group Corresponded the water flow velocity of individual movement were 20 cm/s, 20 cm/s, 10 cm/s; Corresponded the water flow velocity of ounce movement were 40 cm/s, 40 cm/s, 20 cm/s; Corresponded the water flow velocity of universal movement were 60 cm/s, 60 cm/s, 60 cm/s. Although the planting of Potamogeton crispus and Vallisneria natans changed the incipent standards and has a little effect on water turbidity of each incipent standards. Therefore, the planting of Potamogeton crispus and Vallisneria natans can effectively reduce the influence of sediment resuspension on water, effectively fix the sediment and maintain the stability of the lake ecological environment.(2)when the water flow velocity were 0, 10, 20, 40, 60, 80 cm/s and the biomass of submerged plant was 2 kg/m2, both of the submerged plants could restrain the rising of water turbidity at different velocities. The Hydrilla verticillata group had more apparent effect than Myriophyllum spicatum group; at the same velocity, the underwater illumination of Hydrilla verticillata group was stronger than Myriophyllum spicatum group; both of the submerged plants could restrain the rising of Water nutrient at different velocities, the Hydrilla verticillata group had apparent effect than Myriophyllum spicatum group.For the total suspended solid, the inhibition rate was 68% ~ 85%, 33% ~ 50%; For the turbidity, the inhibition rate was 71%~83%, 30%~52%; For the total nitrogen,the inhibition rate was 53%~57%,26%~31%; For the total phosphorus, the inhibition rate was 53%~57%,26%~31%. The control group, Hydrilla verticillata group and Myriophyllum spicatum group Corresponded the water flow velocity of individual movement were 20 cm/s, 20 cm/s, 10 cm/s; Corresponded the water flow velocity of ounce movement were 40 cm/s, 40 cm/s, 20 cm/s; Corresponded the water flow velocity of universal movement were 60 cm/s, 60 cm/s, 60 cm/s. Although the planting of Hydrilla verticillata and Myriophyllum spicatum changed the incipent standards and has a little effect on water turbidity of each incipent standards. Therefore, the planting of Hydrilla verticillata and Myriophyllum spicatum can effectively reduce the influence of sediment resuspension on water, effectively fix the sediment and maintain the stability of the lake ecological environment.