Assessment of Soil Quality for Urban Green Spaces in Chongqing City
|Keywords||The main city of Chongqing urban green space soil qualityassessment|
In this paper, the322different type green spaces samples in topsoil from the nine main city zones and Northern New District of Chongqing city were collected, the collected soil samples were measured, according to the18indexes including Physical and chemical properties and the heavy metal content. Based on the results, the fertility quality and environmental quality in green spaces soil of Chongqing city were assessed.(1) The soil properties and nutrient level in the Chongqing urban green spaceThe pH value in the collected soil samples ranged from4.5to8.8, in which acidic and neutral soil accounted for20.2%, compared to the pH of natural soil, the collected soil samples were characteristic of obvious basified trends; The bulk density varied from0.96g/cm3to1.74g/cm3, the average value was1.42g/cm3, indicating the soil compaction phenomenon was obvious; The organic matter content in the studied soil samples ranged16.3g/kg to44.9g/kg, the average value was14.4g/kg, the36.5%studied soil was less than10g/kg. According to the grading standards in the second national soil fertility survey, the72.4%studied soil samples were nitrogen nutritional deficiencies, the82.8%soil samples were lack of phosphorus; Potassium is a medium level in the samples. On the basis of the planting soil quality standards in Chongqing city (DBJ/T50-044-2005), the tested soil fertility is generally low.(2) The quality evaluation of soil fertility in green spaces of Chongqing cityAt present, the quality evaluation system of the urban green space soil fertility is not perfect. In this paper, using matter-element analysis based on entropy right and principal component analysis composite index, the soil fertility quality of urban green space in Chongqing were evaluated, and the two evaluation methods were studied comparatively.The results from matter-element analysis based on entropy right indicated, the fertility level in the investigated urban green space soil were divided into extreme poor (7.76%), poor (27.6%), normal(47.5%), relatively rich(7.76%) and rich(9.32%).The fertility level in different green soil showed different appropriate situation, of which100%comprehensive green parks,80.0%community park green space,78.6%industrial green,63.9%residential green,63.2%public green space，61.9%topic park green,61.1%road green space and35.7%protective green complied with the appropriate "level".The results from principal component analysis composite index indicated, soil single factor fertility in studied urban green space was in low level generally, and total potassium was relatively abundant. The results weighted composite index evaluation showed the fertility level in the studied green soil of different type was at the intermediate level, and differences in the coefficient of variation is small. The integrated soil fertility in park green space, protective green, attached green and the whole studied area were lower-level and intermediate level, the soil fertility in protective green was lowest.The comparison between the two methods of soil fertility evaluation suggested, the entropy and matter element analysis highlighted the poor quality factor impact on the consolidated quality, and the principal component analysis composite index could reduced evaluation factor effectively, but the method was lacking of highlighting the poor quality factor. The effective integration of the entropy and matter element analysis and the principal component analysis composite index maybe more suitable for evaluation of the quality of urban green space soil fertility.(3) Soil Environmental Quality Assessment in the Chongqing urban greenAccording to the results, the total Cu、Zn、Cr、Pb、As、Hg in the test soil of Chongqing city green space was1.19～116mg/kg,44.1～235mg/kg,10.9～83.2mg/kg,2.34-107mg/kg,1.76～14.5mg/kgand2.53～2639μg/kgrespectively. The spatial variability in the content of various heavy metals were higher, especially in Hg. Refer to the background value of purple soil in Chongqing, accumulation of Zn, Pb, Hg, As in green soil was obvious, and accumulation of Cu Cr was presented in a handful of soil.Refer to The National Soil environment quality specification Level II standard for the evaluation of standard value, the results from single factor pollution assessment showed that Hg pollution was presented in few green soil of the studied area, while no pollution trend was found in Cu、Zn、Cr、Pb and As.The integrated pollution evaluation based on Nemerow index indicated that97.8%urban green space soil in studied area were not polluted by heavy metal, only road green space, a small number of green parks and community parks were polluted mildly, and a handful of industrial green were heavily polluted, generally, the soil environment in urban green space was better.