太湖近代沉积物中重金属元素的累积

Accumulation Characteristics of Heavy Metals in the Sediments of Lake Taihu, China

利用210Pb、137Cs定年技术,对来自太湖不同生态和沉积特征的三个湖区的沉积物柱状样品进行了定年,用ICP—AES分析了沉积物中重金属等元素的含量,分析了太湖沉积物中重金属的累积特征及其成因.污染较重、蓝藻水华暴发频繁的梅梁湾沉积物中的重金属含量在近25年来逐年增加;太湖上游风浪较大的夹浦湖区表层10cm沉积速率大、粒度粗,除表层1cm外,1—10cm沉积物中各种重金属含量都较低,且层间变化剧烈;下游湖区正逐渐草型化的胥口湾除表层3cm外,沉积物中重金属的含量自底层向表层大致呈不断下降的趋势.研究表明,不同年代的太湖沉积物中重金属含量差异很大,明显大于不同湖区间沉积物重金属平均含量间的差异.水动力作用引起的沉积物粒度分异很可能是影响沉积物中重金属积累的一个重要因素.总体上太湖沉积物中重金属的污染比较轻微,但已经有一定程度的Cd污染,梅梁湾沉积物中自上世纪70年代开始明显积累Cd,其他重金属元素的积累也逐渐增加,值得关注.

Accumulation characteristics of heavy metals in sediment cores from three lake areas of Lake Taihu, a typical large-shallow freshwater lake in China, were studied with 210 Pb and 137 Cs isotope dating method. Meiliang Bay of Lake Taihu, a eutrophic shallow bay with a deepest depth of less than 2.6m, occurred cyanobacterium algae-bloom every year and received large amount of municipal sewage and industrial wastewater since the middle of 1980s, has a significant increas trend of the contents of Cd, Cr, Cu, Ni, Pb, and Zn in sediment since the recent 25 years. Jiapu District of Lake Taihu, located in the upper reach of Lake Taihu with a disturbed and yellow water, have a significantly low but also drastically varied contents of heavy metals in sediments of 1 -10cm layer from top to bottom, and a largest sedimentation rate and a largest median particle size at the same layer. Xukou Bay of Lake Taihu, a shallow bay located in the lower reaches of Lake Taihu and gradually become macrophyte-dominant lake in recent 10 years, have a decreasing trend of the contents of heavy metals in sediment from bottom to top except the top 3 cm layer, which the contents of heavy metals abruptly increased. The difference of the content of heavy metals among different sediment time was significant higher than the difference of the mean value of the contents of heavy metals among different sediment cores, which resulted in the different evaluating conclusion of heavy metal pollution in different periods. For example, in the middle of 1980s, it was concluded that no Cd pollution of sediment in Meiliang Bay but there was Cd pollution of sediment in Xukou Bay. However, in 2000, it was concluded that Meiliang Bay was the most serious Cd polluted area in Lake Taihu by sediment quality evaluation. Hydrodynamics also could drastically affect the heavy metals sediment in the large-shallow and frequently wind-induced wave disturbing lake by dynamical size differentiation.