草海湖沉积物中重金属污染现状及生态风险评价

贵州草海湖是典型的高原天然淡水湖泊，属于长江上游金沙江支流的上源湖泊，研究其沉积物中重金属分布特征及生态风险评价对该区域及下游的水质监控与污染防治具有重要意义. 2017年7月采集贵州草海湖柱状沉积物，采用电感耦合等离子发射光谱仪法和双道原子荧光光度计法分析沉积物中Zn、Cd、Ni、Fe、V、Cr、Pb、Cu、As等9种重金属元素的质量分数，并利用地累积指数法、富集系数法和潜在生态风险指数法进行重金属污染评价.结果表明:草海湖表层沉积物各重金属质量分数平均值表现为w（Fe）（31 400.00 mg/kg）> w（Zn）（219.18 mg/kg）> w（V）（59.76 mg/kg）> w（Cr）（56.16 mg/kg）> w（Pb）（54.01 mg/kg）> w（Ni）（33.58 mg/kg）> w（Cu）（20.35 mg/kg）> w（As）（15.41 mg/kg）> w（Cd）（0.84 mg/kg）.表层（0~10 cm）沉积物中w（Fe）、w（Cr）、w（V）、w（As）、w（Cu）、w（Ni）分布较均匀，其元素主要来源于岩石风化、土壤侵蚀等自然源；w（Zn）、w（Cd）、w（Pb）分布相对离散，主要来源于农业、炼锌业和交通运输等人为源；在垂直（0~25 cm）方向上，w（Pb）、w（Cu）、w（V）、w（Ni）以波动型为主，w（Zn）、w（Cd）、w（As）主要为稳定型，w（Cr）和w（Fe）为富集型.重金属污染评价结果显示，草海湖沉积物中元素Zn、Pb均为偏中度污染、Cd为中度污染，其潜在生态风险高低表现为下游 > 上游 > 中游.研究显示，草海湖下游区域为中等潜在生态风险，Cd为主要的潜在生态风险因子，重金属的质量分数主要受土法炼锌和农业施肥等人为活动的影响. 

Pollution Status and Ecological Risk Assessment of Heavy Metals in Sediments of Caohai Lake

The Caohai lake in Guizhou Province is a typical natural freshwater lake in the plateau, which belongs to the upper source lake of Jinsha River tributary in the upper reaches of the Yangtze River. Studying the heavy metals in the sediments is important for understanding the monitoring of water quality and its pollution in the region and downstream area. In July 2017, the columnar sediment samples were collected from the Caohai Lake, and the mass fraction of Zn, Cd, Ni, Fe, V, Cr, Pb, Cu and As were analyzed by using an inductively coupled plasma emission spectrometer with dual channel atomic fluorescence photometer. The pollution of the nine heavy metals was evaluated by the cumulative index method, the enrichment coefficient method and potential ecological risk index. The results showed that the average mass fraction of the heavy metals in Caohai Lake surface sediment was w(Fe)(31,400.00 mg/kg), w(Zn)(219.18 mg/kg), w(V)(59.76 mg/kg), w(Cr)(56.16 mg/kg), w(Pb)(54.01 mg/kg), w(Ni)(33.58 mg/kg), w(Cu)(20.35 mg/kg), w(As)(15.41 mg/kg), w(Cd)(0.84 mg/kg). The distribution of w(Fe), w(Cr), w(V), w(As), w(Cu) and w(Ni) in the surface sediments (0-10 cm) was relatively uniform, and the elements mainly came from natural sources such as rock weathering and soil erosion. The distribution of w(Zn), w(Cd) and w(Pb) was relatively discrete, which mainly came from human sources such as agriculture, Zn smelting industry and transportation. As for the vertical (0-25 cm) direction, w(Pb), w(Cu), w(V) and w(Ni) were mainly undulatory type, w(Zn), w(Cd) and w(As) were mainly stable type, while w(Cr) and w(Fe) were enrichment type. The heavy metal pollution evaluation results showed that the Zn, Pb and Cd in the sediments of Caohai Lake were moderate pollutants, and the potential ecological risk was downstream, upstream and midstream from high to low. The study indicated that the downstream area of the Caohai Lake was a moderate potential ecological risk, Cd was the main potential ecological risk factor. Meanwhile, the heavy metal quality score was mainly affected by human activities, such as Zn smelting and agricultural fertilization.