干旱区城市化对生态系统碳库的影响——以乌鲁木齐市为例

城市化是影响区域生态系统碳循环的主要原因,也是评估生态系统碳循环的最大不确定因素。论文利用1990与2010年Landsat TM数据,基于V-I-S城市土地覆被模型和决策树分类法,获得乌鲁木齐土地变化时空格局;结合野外实测数据和文献检索得到研究区不同土地覆被类型的土壤与植被碳密度,估算了城市土地变化对生态系统碳库的影响。结果表明：1）1990—2010年间,乌鲁木齐城市不透水地表（impervious surface areas, ISA）以中部南部内部填充与北部扩张的形式约增加62%,主要占用农田（27%）与荒漠（62%）。2）乌鲁木齐市生态系统碳库主体（95%）分布在土壤中,城市土地覆被变化导致约25%的碳库损失,由农田、裸土/残存荒漠以及城市绿地转变为ISA解释了68%的土壤有机碳和63%的植被碳损失量,其空间分布与ISA的扩张相一致。城市植被及其土壤具有较高的碳密度,合理的城市规划可以抵消部分因土地变化而损失的生态系统碳。

The Impact of Urbanization on Ecosystem Carbon Storage in Arid Area

Urbanization is one of the main factors that influence the regional ecosystem. However, the paucity of observation on the soil organic carbon (SOC) beneath urban impervious surface area (ISA) limits the estimation on the implication of urban land conversion in regional carbon cycle, especially in the arid regions. In this paper, urban land covers (water, ISA, greenspace, cropland, and bare ground, remnant desert) and land cover conversion of Urumqi, Xinjiang, China was estimated using the models of Vegetation-Impervious surface-Soil for urban land covers, linear spectral mixture analysis, and decision tree classifier based on Landsat TM/ETM of 1990 and 2010. The impact of urban land conversion on the ecosystem carbon storage was estimated based on the SOC and vegetation carbon density that obtained from the field observation and literatures. The dominant land conversion was the ISA expansion, which was tripled during 1990-2010, mostly sprawling in the north, and infilling in the southwestern Urumqi. The ISA expansion mainly occupied the bare soil/remnant desert (62%) and cropland (27%). It was found that more than 95% of urban ecosystem carbon stored in the soils, and 48% of which was in the soil under ISA. Land cover conversion during 1990-2010 resulted in a total of 25% carbon loss, in which converting of bare soil/remnant desert and cropland into ISA explained 68% of the total SOC loss and 63% of the total VEGC loss, whose spatial distribution was consistent with the spatial distribution of land conversion. Urban ecosystem carbon sequestration could be improved by intensive management and reasonable planning of the proportion between urban ISA and green space, which could make up for part of carbon loss caused by land conversion.