The response of soil characteristics on urban land-use expansion during rapid economic development and urbanization of the city in China

At a stage of rapid economic development and urbanization in China, most cities are faced with such serious problems caused by environment deterioration as pollution, space press, afforestation degradation and disordering. Kunshan City, one of the most economically vigorous regions in China, has suffered a more prominent confliction between urbanization and environmental safety. In this paper, urban land expansion in Kunshan City in the Yangtze River Delta was measured with reference to the Landsat TM data recorded in 1982, 1991, 1995 and 2003 and change in landuse pattern in 1981, 1991, 1995 and 2004 as well as that in nutrients in soils of different purposes between the periods were analyzed to study the effect of urban land-use expansion on soil characteristics. To get a better understanding of soil nutrients, heavy metal content and pollution, on-the-spot investigation, sampling and laboratory analysis were all conducted, the geo-accumulation factors and revised Nemoro comprehensive index method were adopted for evaluation on the findings. The results show that contents of organic matters, total nitrogen, rapidly available nitrogen and available phosphorus in the soil (except available potassium) have all increased, and the average contents of As, Cd, Cr, Cu, Pb, Ni, Hg, Se and Zn prove to be 8.61, 0.12, 83.53, 32.49, 29.93, 30.45, 0.27, 0.24 and 93.3 mg kg^-1 respectively, showing degradation in soil quality.