淡水鱼塘中重金属Cu、Zn含量及其综合生态风险水平的年际变化趋势分析

Analysis of interannual variation of Cu,Zn contents and comprehensive ecological risk level in polycuture fish ponds

为了解淡水混养鱼塘中重金属Cu、Zn的含量变化趋势及潜在生态危害程度,连续4年采用火焰原子吸收分光光度法对混养鱼塘的水体及表层(0~5 cm)沉积物中Cu、Zn含量进行监测,并用3种不同的方法分别对监测结果进行变化趋势分析和潜在生态危害程度评价。结果表明,鱼塘水体及表层沉积物中Cu、Zn的空间分布差异不显著,但时间分布差异显著,Cu、Zn含量随着养殖时间的延长而增高;水体中Cu、Zn含量均达到国家地表水水质(GB3838-2002)Ⅱ级水标准,其中Cu质量浓度平均含量为0.0691 mg/L,最高浓度为0.1605 mg/L,超过《渔业水质标准》(GB11607-89),超标率为96.9%;Zn质量浓度平均含量为0.1535 mg/L,最高浓度为0.4850 mg/L,超标率为37.5%;表层沉积物中Cu、Zn质量浓度平均值分别为64.8722、295.1020mg/kg。地积累指数评价结果显示,Cu、Zn 4年均值地积累指数分别为0.996和1.864,污染程度Zn>Cu,Cu污染程度为轻度偏中度污染,Zn污染程度为轻度中度污染;潜在生态风险评价结果显示,Cu、Zn的潜在生态危害系数(Ei r)均低于40,综合潜在生态风险指数(RI)为13.769~26.201,平均为21.596,为低生态风险。4年中Cu、Zn的RI呈逐渐上升趋势,表现为2012年>2013年>2014年>2011年。无量纲分析结果显示,2011年和2012年养殖鱼塘水体中Cu、Zn含量均高于表层沉积物中二者含量,2013年和2014年表层沉积物中Cu、Zn含量均明显高于水体中含量。相关性分析表明,淡水养殖池塘中重金属Cu、Zn的来源相同,在水体和表层沉积物之间的迁移方向一致但迁移途径不同,水体和表层沉积物中的总磷含量可能是影响Cu、Zn迁移的主要因子。

The contents of two heavy metals （ Cu and Zn ） in water and surface sediments （ 0-5 cm ） in polycuhure fish ponds were measured by Flame Atomic Absorption Spectrophotometry for four consecutive years, in order to investigate the content change trend and their potential ecological risks, by three different methods. The results showed that the spatial distribution differences of Cu and Zn in fish pond water and surface sediments were not significant, but the time distribution differences were significantly different, the heavy metal contents increased with culture time increasing. In water, the contents of Cu and Zn were relatively lower than the national water standards of class Ⅱ （GB3838-2002） , the average concentrations of Cu and Zn were 0.0691 mg/L and 0.1535 mg/L, the highest concentrations were 0.1605 mg/L and 0.4850 mg/L, the exceeded standard rates of Cu and Zn were 96.9% and 37.5%, respectively. In surface sediments, the average contents of Cu and Zn were 64.8722 mg/kg and 295.1020 mg/kg. The average Ig^o of Cu and Zn for four years were 0.996 （ slight to partial moderate pollution ） and 1.864 （ slight to moderate pollution ） . The potential ecological risk indexes （ Eir ） of Cu and Zn were lower than 40, the comprehensive potential ecological risk indexes （ RIs ） were 13.769 to 26.201, and the average was 21.596, indicating that the potential ecological risks were slight. The RIs of Cu and Zn had gradual upward trend within four years, as follows ： 2012 〉 2013 〉 2014 〉 2011. The results of dimensionless analysis displayed that the Cu, Zn contents in water were higher than those in surface sediments in 2011 and 2012, and was lower than those in surface sediments in 2013 and 2014. Correlation analysis showed that in freshwater ponds, the sources of Cu and Zn were the same, the migration direction of Cu and Zn was consistent but the migration ways were different between water and surface sediments, the total phosphorus content would be the main factor affecting the migration of Cu and Zn.