Characteristics and Driving Forces of Spatial Expansion of Oasis Cities and Towns in Hexi Corridor, Gansu Province, China

This paper presents an integrated study of urban spatial expansion in the Hexi Corridor, Gansu Province, China based on TM, ETM remote sensing data in 1987, 1990, 1995, 2000, 2006 and 2011. The study explores the characteristics of urban spatial expansion and dynamic mechanism by using expansion speed index, expansion intensity index, compact index, fractal dimension, and extended flexibility index. We built the index system of influencing factors of urban spatial expansion by using the grey incidence model. The results showed that urban spatial expansion rate in the Hexi Corridor has been on the upward trend since 1987. Expansion intensity showed an obvious upward trend, however, the upward trend varied in different urban areas. In addition, the urban structure was loose relatively, but the urban compactness was more obvious. The urban spatial form tended to be simple, and the urban land use tended to become more intensive. Urban spatial expansion experienced several stages: padding internally, external expansion and padding internally. The main driving factors of urban spatial expansion are not the urban water resources and the oasis scale, but one or several factors such as economy, traffic, population, resource and national policy.

荒漠绿洲过渡带自然沙地开垦为灌溉农田后土壤硝化、反硝化速率及其影响因素

为阐明干旱区绿洲不同开垦年限农田土壤硝化、反硝化活性及其影响机制,选取河西走廊典型荒漠绿洲边缘不同开垦年限(15、30、50、80、100、150年)农田及未开垦沙地(开垦年限为0年)为研究对象,对比分析表层(0-20 cm)土壤硝化反硝化过程差异及其与环境因子的关系.结果表明,土壤硝化潜势和反硝化潜势均随开垦年限的增加呈先增加后降低的趋势,土壤硝化潜势和反硝化潜势最大值分别出现在开垦80年农田(101.4μg g^(-1) d^(-1))和开垦100年农田(0.93μg g^(-1) d^(-1)),且未开垦沙地土壤硝化潜势和反硝化潜势均显著低于开垦农田(P<0.05).相关分析表明土壤硝化潜势和反硝化潜势均与土壤养分、土壤含水量及土壤粒径组成呈显著相关(P<0.05).土壤硝化反硝化潜势与环境因子间的回归分析表明,环境变量分别解释了硝化潜势和反硝化潜势变化的69.7%和75.7%.其中总氮(TN)、氨氮(NH_(4)^(+)-N)、pH、土壤含水量(SM)和砂粒含量是土壤硝化潜势变化的关键,而有机质含量(SOM)、硝氮(NO_(3)^(-)-N)、pH和黏粒含量是土壤反硝化潜势变化的关键.可见,耕种可显著改善土壤性状,提高土壤水分及养分含量,提高土壤硝化、反硝化能力.(图8参30)