三峡库区香溪河库湾沉积物重金属污染特征

2010年3月在三峡水库香溪河库湾获取了无扰动沉积物柱状样,在香溪河口的长江干流(长江右岸)获取了表层沉积物样,现场进行了环境因子测量和室内粒度分析、矿物分析、重金属元素含量分析。沉积物矿物以绿泥石、伊利石和石英为主,占到全部矿物的65%左右。柱状沉积物pH值随深度增加呈现变小的趋势,Eh值也有随深度减少的趋势,反映了环境还原性加强。R-型因子分析结果表明:重金属元素的含量随粒径变细、绿泥石和伊利石含量增加而增加,而随石英、白云石含量增加而降低;且重金属元素含量变化与pH值密切相关,当pH值下降时部分重金属容易重新释放出来而进入环境中。库湾下游具有较中上游高得多的重金属含量,沉积物中重金属的污染程度为无污染到轻度污染,且轻度污染出现于下游至干流。三峡水库蓄水前香溪河沉积物中重金属含量顺序大致为Zn>Pb>Cu>As>Cd,而蓄水后香溪河及干流沉积物均表现为Cu含量高于Pb。

CHARACTERISTICS OF HEAVY METAL POLLUTION IN SEDIMENTS AT THE XIANGXI BAY OF THREE GORGES RESERVIOR

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.