Aquatic vegetation has a significant impact on water currents. To evaluate the effects of changes in the aquatic vegetation on water currents of different velocity, a 3-D hydrodynamic model was then developed by taking into consideration of the additional hydraulic resistance of the aquatic plants. The Navier-Stokes equations were then solved using the SIMPLE method and the k-ε turbulence model. Calculations using the established models were used to forecast the vertical distribution of the horizontal velocity and horizontal flow under the transmission conditions of the South-North Water Diversion in the Nansi Lake. And comparative calculation for the flow velocity was also performed using the simplified method of assigning a high roughness coefficient to the lake bed in the same area. Results suggest that adding additional hydraulic resistance of the aquatic plants is feasible. The calculation errors between simulation result and the field observed data are smaller than 15%, while, those errors are up to 35% if the influence of aquatic vegetation is dealt with the simplified method.
The potential effects of nanoscale CuO(nCuO),nanoscale ZnO(nZnO) and their mixtures on Daphnia magna were investigated,including 48-h acute toxicity and 21-d chronic toxicity tests as well as a feeding experiment.The results of acute toxicity show that nCuO/nZnO mixture was the most toxic followed by nCuO and nZnO.The nanoparticles(NPs) inhibited both the growth and reproduction of Daphnia magna during the testing period.Concentration dependence was apparent in all the cases and the intrinsic rate of natural increase was confirmed to be a very sensitive parameter to NPs exposure.Binary mixture appeared to be more toxic than the corresponding individual exposures at most cases except for the feeding behavior.
This paper reviews the removal of contaminants including nutrients,metals and organic pollutants by vegetations in aquatic environments.The removal efficiencies are considered with respect to 16,19 and 14 kinds of different aquatic plants,respectively in three tables.Due to different characteristics,the removal effects of plants on contaminants from the overlying water differ greatly.The vegetation can improve the water quality mainly through two ways:(1)to adsorb and absorb pollutants from water,(2)to prevent pollutants from releasing from sediment.The contaminant removal mechanisms of vegetations and related physical,chemical and biological effects are discussed.The effects of vegetations on the contaminant removal are found to depend on the environmental conditions,the number and the type of plants,the nature and the chemical structure of the pollutants.In addition,the contaminant release and removal by vegetations under hydrodynamic conditions is specially addressed.Further research directions are suggested.
With the current rapid economic growth, heavy metal pollution has become one of the key issues in the Taihu Lake. Although heavy metal pollution levels and distributions of the Taihu Lake have previously been described, an effective model to describe the transport process of heavy metals between the water column and sediment bed for this lake is not available. It is known that heavy metals in the water column can be related to the resuspension of sediment in the lake bed. In this study, we set up a coupled model of relating hydrodynamics, sediment and heavy metals based on Environmental Fluid Dynamics Code (EFDC), and applied it to Taihu Lake, China. For calibration and validation of the model, we employed two series of field sampling data taken all over Taihu Lake during April and July of 2009. The results show that the hydrodynamics simulations of the coupled model agree with the observations reasonably well and the sediment and heavy metal model shows similar variation trends during the simulation. Our results indicate that the model can be used for simulating the sediment and heavy metal transport process in the Taihu Lake and here we provide an effective tool for water quality management at small time scales.
