城市化进程中的土壤有机碳库演变趋势分析

土地利用方式变更引起的土壤碳库变化对全球温室效应、全球碳循环有重大的影响。基于1∶250000多目标地球化学调查数据,利用RS遥感影像和GIS统计技术,分析上海市的城市扩张格局及城市扩张进程中的土壤有机碳库演变趋势。根据上海地区1980、2000、2005年3期遥感影像分析,从1980年代开始,研究区城区面积快速扩张,城市生长以原市区为中心向周边扩展,1980~2005年间城市建设用地面积增加1 377 km2。研究区城区表层土壤有机碳分布呈现较大的空间变异性,城区表层土壤有机碳密度为(3.926±1.381)kg m-2,其均值是郊区的1.049倍,是乡村地区的1.255倍,随城市-郊区-乡村空间梯度演替,表层土壤有机碳密度渐趋降低,城区表层土壤呈现轻度积累;相较于第二次土壤普查农林生态系统,当前研究区城区表层土壤有机碳密度均值升高0.239 kg m-2,升幅6.48%。比较1980年前建城区、1980~2000年建城区、2000~2005年建城区与城市郊区土壤有机碳密度分布,新建城区由于土地利用方式变更强烈,土壤结构破坏,土壤有机碳密度基本上处于低值;随着城市用地年限的延长,城市生态系统的演化发展,土壤有机碳密度渐趋增大。研究提供城市化进程中的土壤有机碳库演变趋势信息,可为城市土壤固碳潜力研究提供数据支持,也为推动中国城市生态系统碳循环研究提供参考。

Analysis on Evolution Trend of Soil Organic Carbon Stock During the Course of Urbanization

Soil organic carbon stock change induced by land use changes plays an essential role in the global greenhouse effect and global carbon circulation.This paper studies the urban expanding patterns and the spatial characteristics of soil organic carbon distribution and evolution during the course of urbanization in Shanghai based on 1∶250000 geochemical survey data with the help of remote sensing images and GIS.Urbanization process in Shanghai,China has been quickened greatly since the 1980s,urban areas increased 1377 km2 in the past 25 years and the urban growth patterns circled the central city region according to the remote sensing images acquired in periods of 1980,2000,2005.The topsoil organic carbon density in urban area was(3.926±1.381) kg m-2,which meant density was 1.049 times of that in suburb,and 1.255 times of that in countryside and the topsoil organic carbon distribution showed obvious spatial variability.The topsoil organic carbon densities decreased gradually along urban-suburban-countryside in study area and the urban topsoil was slightly enriched with soil organic carbon.Comparing to the data of the second national soil survey in early 1980s,the mean topsoil organic carbon density in urban area increased 0.239 kg m-2 or 6.48%,in the past 20 years.By comparison of soil organic carbon distribution in the central urban area(-1980),urban expanding area(1980-2000 and 2000-2005) and suburban,the soils in central urban area were enriched with soil organic carbon,but the soil organic carbon density in the urban expanding area(1980-2005) declined as a whole due to drastically changing land use.This paper provides the trends of soil organic carbon distribution during the course of urbanization,which may contribute to baseline dada to evaluate regional carbon sequestration potentials precisely and to push forward carbon circulation research on urban ecosystem in China.