北京城区绿地土壤重金属污染评价与空间分析

Pollution Assessment and Spatial Structure Analysis of Heavy Metals of Greenbelt Soil in Beijing Urban Area

为了揭示北京城区绿地土壤重金属污染状况、影响因素和空间结构特征,从而为北京市环境保护和绿地土壤重金属污染防治提供理论依据,采集北京地区公园绿地、道旁绿地、附属绿地和居住绿地等多个绿地类型中的151个表层土壤(0~20 cm)样品,测定了样品中的重金属(Pb、Cd、Ni、Hg、As)含量,综合运用内梅罗污染指数法及地统计分析方法对5种重金属污染状况、影响因素及空间分布特征进行研究。结果表明:北京城区绿地土壤重金属Pb、Cd、Ni、Hg、As质量分数分别为29.89、0.33、23.89、1.42和7.54 mg?kg^(-1)。5种重金属内梅罗综合污染指数为1.19,属于轻度污染,其中Hg单项污染指数为1.54,污染等级为轻度污染,其余4种重金属单项污染指数均在0.7以下,污染等级为安全级。公园绿地土壤重金属污染内梅罗指数为1.81,属于轻度污染,并且存在轻度的Hg污染,污染指数为1.37,道旁绿地、居住绿地和附属绿地均未受到重金属污染。半变异函数拟合结果表明,5种重金属均存在中等强度的空间自相关性,其中Pb和Cd拟合于球状模型,块基比值分别为65.03%和43.12%;Hg拟合于高斯模型,块金比值为41.3%;Ni和As拟合于指数模型,块金比值分别为44.35%和49.96%。另外,Pb、Cd和As表现为各向异性,Hg和Ni表现为各向同性。Ni和As高值区主要分布在北部地区;Pb和Hg高值区分布主要集中在中部,呈现出从中部向外围递减的趋势;Cd高值区分布比较零散,呈不规则斑块状分布。5种重金属污染及空间结构受到随机因素和结构因素的共同影响,受随机因素影响的程度为Pb>As>Ni>Cd>Hg。

In order to reveal the pollution degrees, influence factors and spatial structure characteristics of greenbelt soils heavy metals in Beijing urban area, as well as provide a theoretical basis for Beijing to protect the environment and prevent greenbelt soil polluted by heavy metals. The concentrations of Pb, Cd, Ni, Hg and As in 151 greenbelt surface（0~20 cm） soil samples, which were collected from Park green area, Street green area, Residential green area and Affiliate green area, were detected. Then the influence factors and degrees of pollution and spatial structure characteristics of heavy metals in the soils were analyzed by applying the Nemerow integrated pollution index and Geo-statistics. The results showed that average values of total Pb, Cd, Ni, Hg and As were 29.89, 0.33, 23.89, 1.42 and 7.54 mg？kg^（-1）, respectively. The greenbelt soil was polluted slightly, and the Nemerow integrated pollution index of the four heavy metals was 1.19. Single-factor pollution index of Hg was 1.54, which indicated low pollution level, while all of other four heavy metals posed no pollution and the single-factor pollution index of was all less than 0.7. Park green area was polluted slightly, and the Nemerow integrated pollution index of the four heavy metals was 1.81. Single-factor pollution index of Hg was 1.37, which indicated low pollution level, while none of other three green area had been polluted by heavy metals. According to the semivariogram fitting, the spatial autocorrelation of these four heavy metals was moderate. Pb and Cd fit the spherical model and the ratios of nugget and still were 65.03% and 43.12%, respectively. Hg fit to Gaussian model and the ratios of nugget and still was 41.3%. Ni and As fit the exponential model and the ratios of nugget and still were about 44.35% and 49.96%, Pb, Cd and As were isotropy, Hg and Ni were anisotropy. High-value areas of Ni and As were in the north region, high-value areas of Pb Hg was in the central region, and showed a trend of decreasing in the area, and distribution of Cd was fragmented and looked irregular. The pollution and spatial structure of these five heavy metals were both influenced by structural and random factors, and the degrees of being influenced by random factors were in the order of Pb〉As〉Ni〉Cd〉Hg.