乌鲁木齐不同功能区林带土壤重金属污染特征分析

Characteristics of Heavy-metal Pollution in Forest Belt Soil of Different Functional Zones in Urumqi, Xinjiang

为了揭示乌鲁木齐市林带土壤重金属污染状况,在乌鲁木齐市选取工业区(IZ)林带、道路(RZ)林带、生活区(RZ)林带和公园(PZ)林带等4种功能区林带类型,测定了林带土壤中5种重金属(Zn、Pb、Hg、As、Cr)的质量分数,利用单因子污染指数法和内梅罗综合污染指数法分析了不同功能区林带土壤重金属污染特征。结果表明,乌鲁木齐市林带土壤锌和汞质量分数普遍超过背景值,其超标率分别为92.86%和95.71%,超标倍数为1.58倍和12.79倍;土壤铅、砷和铬质量分数超标率分别为41.43%、7.14%和40%,但总体显示平均质量分数未超过背景值;单项污染指数大小为汞>锌>铅>铬>砷。4种功能区林带土壤锌和砷质量分数为道路林带>工业区林带>生活区林带>公园林带;土壤铅和汞平均质量分数为工业区林带>道路林带>生活区林带>公园林带;土壤铬平均质量分数为工业区林带>道路林带>公园林带>生活区林带。土壤重金属污染综合程度为工业区林带>道路林带>生活区林带>公园林带。从各污染等级样地出现相对频次看,无污染等级的样地仅出现在生活区;重度污染等级的样地在工业区林带、道路林带、生活区林带和公园林带出现的相对频次分别为70.83%、20.83%、35.29%和26.31%;中度污染等级的样地出现的相对频次分别为12.5%、50%、11.76%和42.10%;轻度污染等级的样地出现的频次分别为8.33%、16.67%、35.29%和31.57%;尚清洁等级的样地在工业区林带、道路林带和生活区林带出现的相对频次分别为8.33%、12.5%和11.76%,在公园林带未出现。乌鲁木齐绿化树种组成丰富和植被盖度高的公园林带和生活区林带土壤重金属污染程度较轻,建议在城市化发展的过程中,合理优化布局。选择净化环境功能强的树种是城市林业建设的发展趋势之一。

In this study, we analysed the characteristics of heavy-metal pollution in forest belt soil of different functional zones (industrial, road park and residential) using the single-factor pollution index method and the Nemerow comprehensive pollution index method. The results showed that Zn and Hg contents in the forest belt soil of the city of Urumqi generally exceeded their respective background values, with over-standard rates of 92.86% and 95.71%, respectively, which were 1.58-fold and 12.79-fold larger than the standard values, respectively;the over-standard rates of Pb, As, and Cr contents in the sampled soil were 41.43%, 7.14% and 40%, respectively, although their average contents did not exceed their respective background values. The single-factor pollution index exhibited the following order: mercury>zinc>lead>chromium>arsenic. In the forest belt soil of the four functional zones, the Zn and As contents exhibited the following order: road zone>industrial zone>residential zone>park zone, and the average Pb and Hg contents followed a descending order of industrial zone>road zone>residential zone>park zone. The average chromium content exhibited a descending order of industrial zone>road zone>park zone>residential zone, and the comprehensive level of heavy-metal pollution had a descending order of industrial zone>road zone>residential zone>park zone. In terms of the relative frequency of the sample plots with each pollution level, the plots with a safe level of pollution were only present in the residential zone. The relative frequencies of plots with a heavy level of pollution in the forest belts of the industrial zone, road zone, residential zone, and park zone were 70.83%, 20.83%, 35.29% and 26.31%, respectively, and those with a moderate level of pollution were 12.5%, 50%, 11.76% and 42.10%, respectively;moreover, the plots with a mild level of pollution were 8.33%, 16.67%, 35.29% and 31.57%, respectively, and those with a warning level of pollution were 8.33%, 12.5%, 11.76% and 0%, respectively. We suggested the trees that with strong purifying environmental functions should be priority selection.