摘要
为掌握红碱淖重金属污染水平及其生态风险,我们对红碱淖表层沉积物开展了重金属分析,采用元素富集因子法和潜在生态风险指数法对沉积物重金属进行生态风险评价。结果表明:(1)湖心样品的重金属元素丰度比湖岸样品略高;(2)红碱淖各采样点重金属均处于轻度污染状态,仅Cd存在一定程度的富集;(3)沉积物重金属潜在生态风险指数处于较低水平。
Background, aim and scope As the biggest desert freshwater lake in China, Hongjiannao Lake, located in the southern margin of Mu Us Desert, plays an important role in the regional ecosystem. It is the habitats of Larus relictus which is classifi ed as ＂vulnerable＂ on the Red List of International Union for the Conservation of Nature（IUCN）. However, the degradation of aquatic ecosystem in this region was found to be accelerating in recent years under the context of global warming and the intensifi ed human activities. The ecological risk of heavy metals in the surface sediment of Hongjiannao Lake remains unknown so far. Therefore, the aim of this study is to provide the basic data for protecting the lake ecosystem by assessing the potential ecological risk of heavy metals in the surface sediment of the lake. Materials and methodsTwelve samples of surface sediment in the lake was taken by the Van veen grab sampler. The distribution of sampling sites in the lake were designed to be even to ensure the representativeness of the samples. Cr, Cd, Cu, Pb and Zn were analyzed by ICP-MS. The relative error of this method was controlled within 15% for Cr, 30% for Cd, 10% for Cu, 10% for Pb, and 12% for Zn. As, Hg were analyzed by atomic fl uorescence spectrometry. The relative error of this method was controlled within 10% for As and 25% for Hg. Cr6＋ was measured by diphenylcarbonydraide-spectrophotometer method with the relative error controlled within 15%. Three approaches were used in the assessment of the ecological risk of heavy metals in the surface sediment of Hongjiannao Lake：（1） the comparison of samples in Hongjiannao Lake with the Environmental Quality Standard for Soils in China（GB 15618—1995）（EQSS）.（2） The enrichment factor（EF） to show the state of the enrichment for each element relative to the reference system. The reference system is selected respectively as soils in Shaanxi Province to show the enrichment relative to the local environment, and the upper continental crust（UCC） to show the enrichment relative to the global mean content of upper continental crust. And（3） the potential ecological risk index（RI） to assess the potential risk of the toxicity of heavy metals to the lake ecosystem. Results The result shows that the heavy metals in the surface sediment of Hongjiannao Lake are generally at a low level. The order of content from higher to lower is Cr Zn Pb Hg Cu As Cd. Except for Pb, As and Cr, the coeffi cient variations（CV） of other four metals（Cd, Cu, Zn and Hg） among twelve sites are higher than 0.55 with Cd to be the highest in 0.68. Obviously, the contents of heavy metals of the surface sediments in the center of the lake（sites 7 to 12） are higher than those near the lakeshore（sites 1 to 6）. Discussion Compared with the EQSS, the mean value of each heavy metal is within the upper limit value of the fi rst class soil in EQSS, indicating that the risk of heavy metals to this lake is at a lighter degree. Even for the maximum value of each element among the twelve samples, most of them are within the upper limit value of the fi rst class soil in EQSS, except for Cd. There are only two samples with the maximum value of Cd extend the upper limit value of the second class soil in EQSS. For most elements in the surface sediment of Hongjiannao Lake, the values of enrichment factor are lower than 1, indicating that there is no obvious enrichment for most elements, except for Cd and As. Cd assumes obvious enrichment both relative to soils in Shaanxi Province and to UCC at sites 1, 7, 8, 9, 10, 11. For As, it assumes enrichment only relative to UCC, but there is no enrichment relative to soils in Shaanxi Province, implying that the background content of As in soils in Shaanxi Province is higher than that in UCC. The Cfi value of heavy metals for each sampling site varies from 2.06 to 9.97, with the mean value of 6.04. The RI value of heavy metals for each sampling site varies from 22.52 to 179.18, with the mean value of 93.50. There are six sites（1, 7, 8, 9, 10, 11） where the RI value are higher than 110, indicating that the risk of heavy metals in the center of the lake is light higher than that near the lakeshore. Generally, both the Cfi value and the RI value show that the potential risk of heavy metals in the lake is at a low level. Conclusions The above results show that：（1） the contents of heavy metals of the surface sediments in the center of the lake are higher than those near the lakeshore;（2） generally, the pollution of heavy metals in the lake is at a very low level, with the mild enrichment of Cd; and（3） the potential ecological risk of heavy metals in the surface sediment of Hongjiannao Lake is at a low level. Recommendations and perspectives The assessment provides the basic data for protecting the aquatic ecosystem in Hongjiannao Lake. Although the current risk of heavy metals in the surface sediment is not severe, the strict measures should be taken in the future to forbid the discharge of polluted water into the lake.
出处
《地球环境学报》
2016年第2期173-182,共10页
Journal of Earth Environment
基金
环境保护部"良好湖泊生态环境保护专项"
黄土与第四纪地质国家重点实验室自主部署课题~~
