贵州草海沉积物重金属分布及其对底栖动物群落的影响

Distribution of heavy metals in sediments and its impact on zoobenthos community of Lake Caohai in Guizhou

基于原子吸收和ICP-MS,研究了贵州威宁草海4种重金属Zn、Pb、Cd、Ni的分布规律,并分析了其对底栖动物群落结构的影响.结果表明,表层沉积物中Zn、Pb、Cd 3种重金属含量已超过加拿大环境质量标准,超标样品量分别达到样品总数的82%、65%和47%,可能和周边历史上大规模的土法炼锌有关;草海表层水及孔隙水4种重金属含量均未超过国家I类地表水质量标准,表明污染的沉积物对水体重金属含量影响有限.表层沉积物中Zn、Pb、Cd均表现出湖中心及上游湖口含量更高的趋势,并和有机质呈显著正相关关系(r=0.837,P≤0.01;r=0.785,P≤0.01;r=0.780,P≤0.01),表明有机质在Zn、Pb、Cd的迁移和沉积中扮演了重要角色.在湖心沉积物柱中,Zn、Pb、Cd 3种重金属从剖面上部约10cm往上均有逐渐升高富集的趋势,与草海周边近几十年的大规模土法炼锌历史吻合.不管在表层沉积物还是在沉积物柱中Ni都呈现与其它3种重金属相反的分布规律,可能与Ni主要来源于自然背景有关.底栖动物群落结构调查表明,周边采样点比湖内采样点的底栖动物种类更为丰富,栖息密度也更大,这可能与草海湖内采样点重金属含量远高于湖周边采样点有关,具体影响及机制需要进一步深入研究.

In this study, the concentrations and distributions of Zn, Pb, Cd, Ni in sediments in Lake Caohai from Weining District of Guizhou Province were analyzed in this research based on atomic absorption and ICP-MS, and its influence on zoobenthos community was analyzed. The results indicated that, concentrations of Zn, Pb, Cd in surface sediments exceeded the Canadian Environmental Quality Guidelines The percentage of samples contaminated by Zn, Pb, Cd, were 82%, 65% and 47% respectively. This may be due to the historical zinc smelting activities. But concentrations of heavy metals in surface water and pore water of Lake Caohai were in normal range compared to the National Quality Standard for Surface Water （grade I）, which indicated the influence of heavy metals in contaminated sediments on pore water was limited. Concentrations of Zn, Pb, Cd, in the middle of the lake and at the shore were higher than those in other sampling sites. Pearson correlation coefficients between the content of Zn, Pb, Cd, and organic materials were positive in significant levels （r=0.837,P≤0.01;r=0.785,P≤0.01;r=0.780,P≤0.01, respectively）, which meant the content of organic materials played an important role in transformation and deposition of these heavy metals. Concentrations of Zn, Pb, Cd were rising and accumulating from 10cm to the top of sediment profile in the middle of Lake Caohai, which could match with the history of zinc smelting activities in recent decades. Ni had an opposite correlation with the other three studied heavy metals in both surface sediment and sediment profile, probably because Ni came from the natural background. The survey of zoobenthos community structure indicated that there were more species and higher density of zoobenthos in the surrounding sampling sites than those in the central area. This may suggest a higher concentration of heavy metals in the central area of Lake Caohai. Further studies are needed to justify this.