基于标识指数与敏感性分析的洞庭湖滨湖区地下水重金属污染评价

以洞庭湖滨湖区城西垸为例,采用基于熵权的综合标识指数模型,探讨了滨湖区地下水中各重金属污染现状,分析了综合评价结果对各评价因子的敏感性程度,并针对不同评价方法的评价结果进行了对比. 结果表明:基于GB/T 14848—1993《地下水水环境质量标准》Ⅲ类水质标准,研究区ρ(Pb)、ρ(Fe)、ρ(Mn)的超标率均达到67%,最差水质类别分别为劣Ⅴ类、Ⅳ类和Ⅴ类；地下水重金属污染空间变异明显,其中湘江西支地下水污染最为严重,综合标识指数(4.126)最大,属于Ⅳ类水质,洞庭湖区次之,湘江东支地下水污染程度最轻(3.515),并且两支流地下水由上游至下游呈污染逐渐减轻的趋势；敏感性分析表明,综合评价结果对ρ(Pb)和ρ(Mn)的敏感性较强,敏感性系数分别为0.0539和0.0479,说明Pb、Mn是影响城西垸地下水水质变化的主要重金属污染物. 

Assessments for Heavy Metals Pollution of Groundwater at Lakeside of the Dongting Lake Based on Identification Index and Sensitivity Analysis

The west embankment of Xiangyin county in the lakeside of Dongting Lake was taken to study the pollution level of heavy metals in the groundwater. The pollution status of various heavy metals in the groundwater was studied with the comprehensive identification index based on entropy weight model system and the sensitivity analysis of the comprehensive evaluation results to each evaluation factor. A comparative study was carried out according to the results from different evaluation methods. According to class Ⅲ level of GB/T 14848-1993Water Environment Quality Standards of Groundwater, the contamination rate of the heavy metals in this area reached 67%, and the worst levels of water quality were class Ⅴ, class Ⅳ and inferior class Ⅴ, respectively. The pollution levels of heavy metals showed a remarkable spatial heterogeneity. The west tributary was the most seriously contaminated (pollution index was 4.126, belonging to class Ⅳ), followed by the Dongting lake district, and the east tributary lightest (pollution index was 3.515). In addition, polluted conditions gradually aggravated from the upstream to the downstream in the two tributaries. Sensitivity analysis suggested that comprehensive evaluation was sensitive to Pb and Mn, and their sensitive coefficients were 0.0539and 0.0479respectively. This result indicated that Pb and Mn are the major metal pollutants to influence the groundwater quality of the west embankment.