Abstract:

Three undisturbed sediment cores (XX02,XX06 and XX08 located at the upper,middle and lower stream of Xiangxi Bay,respectively) and one surface (XXCJ located at the main stream of the Yangtze River,near the right bank of the river)),were acquired in March,2010.The environmental factors were measured on the spot,and the analysis of grainsize,minerals and metal element content were carried out in the lab.Chlorite,illite and quartz account for~65% of all minerals in sediments.Values of pH and Eh profiles from sediment cores are decrease with increasing depth.Contents of heavy metal elements are in the order of Zn>Cu>Pb>Ni>As>Cd at XX02 and CJXX,but Zn>Cu>Ni>Pb>As>Cd at XX06 and XX08, which shows a relatively reducing contents of Pb and Cu.Factor analysis shows that contents of metal element increase with the smaller grainsize and higher contents of chlorite and illite,and decrease with higher contents of quartz and dolomite.Contents of heavy metal elements in sediment samples have a close relation to the responding pH values,which may indicate metal elements are released into the environment under the situation of a lowering pH value. Contents of the heavy metal elements in the sediments at lower stream of Xiangxi Bay are much higher than those at middle and upper stream.The samples from XX02 and CJXX have better relationship according to the clustering analysis.Sediments are free from contamination or lightly contaminated by heavy metals,and the latter appears in the lower river and the main river.The contents of heavy metal in sediments from Xiangxi Bay follow Zn>Pb>Cu >As>Cd before the impoundment of Three Gorges Reservoir.However,contents of Cu in sediments from both Xiangxi Bay and the mainstream of the Yangtze River are higher than those of Pb after the impoundment of Three Gorges Reservoir