兰州市表层土壤中汞的生态地球化学评价

对兰州市1663km2范围内的表层土壤和大气干湿沉降空间分布模式进行了分析，认为表层土壤中Hg的含量差异较大，其中Hg的平均含量为0．14×10^-6，最高值为6．38×10^-6。对土壤中Hg的存在形式进行了研究，认为燃煤是其主要来源。大气总汞浓度年平均值为28．62×10^-9，其中采暖期为48．48×10^-9，非采暖期为9．42×10^-9。根据国家土壤环境质量标准，兰州市№环境质量达到Ⅰ级标准的土壤面积为1376．1km2，占研究区总面积的82．75％；Ⅱ级土壤面积246．8km2，占14．84％；Ⅲ级土壤面积31．7km2，占1．91％；Ⅳ级土壤面积8．4km2，占0．51％。Ⅲ、Ⅳ级区域主要分布在兰州市西固区石化厂及其附近、七里河区西关十子一城关区二热电厂。

THE EVALUATION OF Hg ECOLOGICAL GEOCHEMISTRY OF SURFACE SOIL IN LANZHOU

Based on analyzing the spatial distribution patterns of surface soil and atmospheric(dry and wet) deposition of Lanzhou covering 1 663 km2,the authors concluded that the average content of Hg in surface soil is 0.14×10-6 with the peak value being 6.38×10-6,and that burning coal is the main source of Hg in surface soil.The annual mean value of total Hg content in air of Lanzhou is 28.62×10-9,whereas the value during the heating period and non-heating period is 48.48×10-9 and 9.42×10-9,respectively.Ac-cording to the National Environmental Quality Standards for Soil,the area of Grade I Hg quality in surface soil of Lanzhou reaches 1 376.1 km2,while Grade Ⅱ,III,Ⅳ possesses 246.8 km2,31.7 km2 and 8.4 km2 respectively.The area of Grade I accounts for 82.75% of the whole study area,while the percentage for GradeⅡ,III,Ⅳ is 14.84%,1.91% and 0.51%,respectively.It is found that the areas of Grade III and Ⅳ are mainly distributed around the Petrochemical Plant of Xigu District and Lanzhou Second Heat and Power Factory in Chengguan and Qilihe districts.