郑州市城市化进程中土壤环境质量评价

Soil environmental quality evaluation of Zhengzhou City on the way towards urbanization

以郑州市为例,揭示城市化过程对土壤环境质量的影响。对距市中心不同距离的表层土样的重金属(Pb、Cr、Cd、Hg和As)含量进行分析。根据土壤环境背景值标准对土样进行污染评价,同时采用克里格插值方法分析土壤环境质量指数分布的空间特征。结果表明,城市扩张对土壤中重金属Cr含量的影响最大,对As有一定影响,而对其他重金属含量的影响较小。样点表层土壤中各重金属含量均有超过背景值现象,其中Cr平均含量远高于背景值,为主要污染因子;Pb为轻污染;Cd、Hg和As平均含量小于背景值。各重金属单因子污染指数的空间分布特点不同,其中Cd在郑州市西部为轻污染;Hg在北郊为轻污染;Pb为较普遍的轻污染;As存在点源污染;Cr在绝大部分地区属重度污染。因此,郑州市在城市化进程中应把Cr作为严控指标。

The paper is aimed at reporting our investigation of the strong impact of urbanization process on the soil environmental quality changes in the suburbs of Zhengzhou City.Our investigation is mainly focused on the changes of concentrations of the samples collected from the topsoil in the suburbs in different distances from the city center,such heavy metals,as Cd,Hg,Pb,As and Cr.Our evaluation is done on the basis of the environmental background criteria by means of single factor index method.In addition,we have also paid close attention to the spatial varieties of the soil pollution in terms of heavy metals with the Kriging interpolation method.The results of our investigation indicate that the expansion of the urban areas has had strong impact of Cr on the soil quality, along with a certain influence of some other heavy metals.The average content of heavy metals（Cr,Pb） in the soil has statistically exceeded the background value,with the concentrations of Cr far beyond its background criterion.The content of Pb is considered to be slightly polluted,whereas that of other heavy metals remains below the state-stipulated pollution standards.More accurately speaking,in terms of the single factor index spatial distribution,it is highly noticeable that the pollution of heavy metals have very different features,in which,the single factor index of Cd beyond grade Ⅱ in the western suburb of Zhengzhou,Hg beyond Ⅱ in the northern suburb while the pollution of Pb belongs in class Ⅲ in all the research areas on the whole,and the pollution index of Cr belongs to grade Ⅴ in most parts of the city＇s suburbs.Literally speaking,the pollution of Cr reaches severe level,which can be considered as a dominant element leading to the deterioration of soil quality.Therefore,the paper considers that heavy metals have presented some accumulative effect in degrading the soil quality with the development of industrialization and fast speed of urbanization in our country.Perhaps,in some sense,it can be said that urbanization has become the main impacting factors of heavy metals on the qualities of the arable land resources and soil environment.Therefore,urgent measures should be taken to protect the existing cultivated land and soil environmental quality.While in the city of Zhengzhou,the process of urbanization should be taken as chromium and control indicators of the soil quality degradation.