Pollution Characteristics Of The Sediment Of The Hangzhou Section Of The Grand Canal,China, And Its Pollution Releasing Mechanism And Ecological Effects

In this paper, pollution characteristics of the sediment of the Hangzhou section of the Grand Canal was investigated, the ecological risk of the sediment was evaluated with potential ecological index, and the releasing mechanism of pollutants from the sediment was studied with modeling experiments. Moreover, the ecological toxicology of the land application of the sediment from the Hangzhou section of the Grand Canal and the downward movement of the pollutants in soil system were studied by pot experiments and soil column leaching experiments. Investigation of the pollution of the sediment showed that, the sediment had been polluted by heavy metals, mean values of Cd, Zn, Cu, Pb, Hg, As and Cr were 6.50, 6.46, 4.60, 2.81, 2.32, 1.29, and 1.17 times higher than the background values, respectively. The sediment also contained plenty of nutrients. Concentrations of organic carbon (0.0.), available phosphorus, available potassium and total nitrogen were 11.3, 5.4, 3.3 and 1.4 times higher than the paddy soil near the canal, respectively. Owing to the complex pollution sources, accumulating extents of the pollutants in the sediment varied drastically in different section of the canal. Although the connecting section between the canal and Qiantang River was newly dug section, its sediment also been polluted owing to the back-flux of the polluted water from the downstream. Concentration of 0.0. in the sediment of the downtown section of the canal was significantly high, and the concentration of Zn in industrial section of the canal was also remarkably high. Concentration of 0.0. was significantly higher than that investigated at 15 years ago, showed that the pollution abatement engineering which taken on in the last fifteen year hadn抰 effectively decreased the organic pollution sources. However, compared with the investigation of 15 years ago, the concentration of Zn in the sediment significantly decreased. Organic pollution in the top layer sediment had seriously affected the bottom layer, and the downward movement of Hg in the sediment was also remarkable. Ecological risk evaluation with potential ecological risk index showed that, the most dangerous ecological risk factor of the sediment was Cd, followed with Hg and Cu. Ecological risk of different section of the canal was also drastically varied. The most ecologically dangerous sediment was that from the industrial section of the canal. Fractionation of the Cu and Zn in the sediment showed that, Cu in the sediment mainly presented in residual fraction, more than 50 percent of the total Cu in the sediment presented in residual fraction. Reducible fraction was another major fraction of Cu. More than 60 percent of Zn in the sediment was presented in acid extractable fraction. Principal factor analysis of the pollutants showed that, most of the pollutants in connecting section between the canal and Qiantang River and in the countryside section of the canal were homologous, while those in the urban section sediment were complex, reflecting the complex pollution sources. In the releasing experiment, releasing-adsorption balance of Cu was arrived in 2 days, which was significantly quicker than that of Zn. Equilibrating concentrations of Cu in overlying water (OW) releasing from the sediment sampled from different section of the canal were quite different. Concentration of Cu in OW releasing from the sediment of industrial section of the canal was significantly higher than that releasing from the sediment of downtown section, so did the Zn. Owing to the rel...