Migration Of Heavy Metals In Ning Section Of The Yellow River Simulation Studies

In nature, rivers are usually the sink for most of the pollutants. And sediment and water flow are the main carriers of them, especially for heavy metals, which is a kind of heavy toxic and hardly degradable pollutants. As heavy metal pollution soaring to be severe, the study on the transport and fate behavior of heavy metals in aquatic environment is becoming significant and intense day by day. Overall, heavy metals change into two main states when they are discharged into water bodies, they are absorpted state and water soluble state. Although the later state is extraordinarily less than the former, the water soluble form can transport a long distance, and then, directly threat the health of humans through drinking water and aquatic products and so on. According to the results of many researches, in most cases, the heavy metals can be strongly absorbed onto the surface of suspended particles to be the main form of heavy metals in waters. And this process is impacted by many factors, including adsorbent and adsorbate characteristics and environment conditions. When one or more of the factors change, heavy metals will transform between these two states. Thus, quantitively study the relationship between the factors and the absorption rate K will make contribution to clearly understanding the transport and fate of heavy metals in the river. Otherwise, simulation and prediction of the transport behavior of the water soluble heavy metals will supply effective references for decision making when response to the River Pollution Emergencies.This thesis1) analysed the spatial distribution of the absorpted and water soluble states of heavy metals from Bayangaole to Toudaoguai cross section using the measured data in July2011, and specially assessing the ecological risk of the seven metals in suspended and sediment phases using the potential ecological risk assessment method.2) set up a comprehensive effect model to describe the co-function among the factors and the absorption rate K in the reach from Bayangaole to Toudaoguai basing on the data from references and the measured data.3) simulated the hydrodynamics and the transportation of the water soluble heavy metals in the reach of Yellow River from Bayangaole to Toudaoguai using EFDC (Environmental Fluid Dynamics Code).The conclusions of these researches are listed as follow:(1) The results of the ecological risk assessment show that the risks of the heavy metals contamination in the suspended and sediment phases are severe. The main contributor is Hg, followed by Cd and As.(2) K decreases with the initial concentration Co, particle size D and ionic strength I. And the curves exhibit flat trends. K increases with the sediment concentration CN, and exists an optimum value. The curve of K increasing with pH exhibits quick, slow and quick three stages. K appeared linear growth with temperature.(3) According to the analysis above, a comprehensive effect model is set up based on the relationship of K and the factors. Then, a comprehensive effect model, which suitable for the part of Yellow River from Bayangaole to Toudaoguai, is set up using the measured data. The values of K on the cross section of Bayangaole are0.621,0.628,0.786,0.744,0.663,0.645,0.644,0.812,0.753,0.723,0.792,0.753from January to December. And K increases with the sediment concentration in the range.(4) The outcomes of the EFDC hydrodynamics simulation prove that this model is reliable and effective because of the high consistency between the calculated value and measured value of the water level.(5) In the part of water quality simulation, this thesis chose three attenuation coefficients,1.0×l0-7s-1,1.0×10-6s-1and1.0×10-5s-1, to simulate the transport behavior of water soluble heavy metals in the part of Yellow River from Bayangaole to Toudaoguai. The degradation of1.0×10-5s-1is the highest. And for the same attenuation coefficient, as the contaminants transport to downstream, the degree of degradation begins to decrease from the15th day. At the same time, the contaminated zone is growing because of the water flow diffusion function. Otherwise, the transportation speed is higher in the part of which the river width is smaller, for the reason that water flow rate in this part is larger.(5) The analysis on the Sanhuhekou cross section shows that in the three time periods,106-140d,197-231d and289-323d, the incipient five days accumulative volume of the second time period is lowest, which leading to the latest arriving time, the lowest pollutant concentration, and the longest retention time.(6) According to the computational results of EFDC, the time when the pollutants arrive at the target cross section, the location and length of the contaminated zone can be judged; thereby, coping measures can be decided before the pollutants arrive.