Xi'an Park Soil Heavy Metal Concentration Levels And Physicochemical Properties

With rapid development of urbanization, Environmental quality of urban soils is becoming increasingly concerned. Urban soil that was regarded as the major factor of sustainable development of urban areas is the important part of ecosystem, site and nrtrition supplier for vegetation. The city park is the main places for the citizen to relax and to get in touch with the natural world, however, the city park soil is facing the environmental problems from urbanization process, such as quality of soils is becoming worse, its roles for production and ecology is changing or losing. At the same time, the accumulation of heavy metals in the soil will have a negative impact on human health, especially children. So the study of the physical -chemical property and heavy metal concentration levels in urban park soil, for discussion of urban soil quality and the sources of heavy metals, evaluation of soil quality and soil pollution have important practical significance.The study concentrated on 19 parks in Xi'an city. After field investigation and laboratory analysis of soil samples, systematically studied the physical-chemical property in Xi'an typical city park, such as particle size, pH, conductivity(EC), loss on ignition, magnetic susceptibility, CaCO₃ contents, available P and available K contents and constant elements of soil. The concentration of As, Cu, Mn, Pb, Zn, Co, Ni, Cr and Fe in soil was analyzed by using X-Ray fluorescence spectrometry. The integrated fertility evaluation was assessed by using the modified synthetic pollution index method. The contamination level and ecological risk of heavy metals in soils were assessed by using the synthetic pollution index method and potential ecological risk index method. Using correlation analysis to discuss the relationship between heavy metals and the relationship between soil physical - chemical property and heavy metal contents. The main conclusions of this paper is as follows:(1) Xi'an Park soil texture type is silty loam, the average particle size is composed of 22.99% clay, 74.15% silt , 2.82% sand; the LOI in every park has smaller difference, average value is 3.89%; soil in most park was alkaline, in some areas showed strong alkaline; conductivity (EC) values from 0 to 0.5 ms / cm that within the scope of garden plant safe to grow , there was no problem of salinization; calcium content in the range of 27.78～126.19g/kg ,average value is 95.96 g / kg; available phosphorus and potassium contents are enrichment in surface soils of Xi'an Park. The results of comprehensive evaluation of soil fertility show that the overall fertility status of soil at the middle level (1.0≤P <1.5). The discrepancy of fertility coefficient in different park is not evident.(2)Compared to Shaanxi Province background value of soil, As, Cu, Mn, Pb, Zn, Co, Ni, Cr, Fe elements in the soil in Xi'an park have been marked accumulation, followed by intensity of Pb> Cu> Co> Fe> Zn> Cr> Mn> Ni> As. Pb in the Revolutionary Park, Lianhu Park, Central South Park, Central west Park reach a higher level of pollution; Zn in Lianhu Park, Central South Park reach the higher the degree of pollution; Cu in Lianhu park and Laodong park highly contaminated in soil. The results of synthetic pollution index method show that all the Xi'an city park are subject to different levels of soil pollution, including four parks are heavily polluted; 9 parks are medium pollution; the rest of 6 parks are light pollution. Most of heavily polluted parks are located within the walls; parks between the walls and the second ring, which the majority belonged to the middle of pollution. Potential ecological index method shows that the parks in Xi'an ecological risk of heavy metals in soils at the middle level, the order of every elements potential ecological risk index is Pb = As> Cu> Cr> Mn> Zn.(3) The study of different depth of the soil in Xi'an city park have shown that, due to the construction of city, such as construction, road repair, etc., as well as industrial waste, solid waste, transportation and other air emissions, urban soil profile often suffer serious change, there are many different source material is mixed in soil, and ultimately lead to the natural soil was damaged, many soil profile upper and lower layers didn't have genetic contact, the distribution of heavy metals content in the profile is irregular.(4) In soil physical-chemical indicators associated with the heavy metal contents analysis, the correlation among pH, loss on ignition, low-frequency magnetic susceptibility, high-frequency magnetic susceptibility, frequency dependent susceptibility, CaCO₃ contents, clay, silt, sand and heavy metal contents is better, reflecting the above-mentioned physical-chemical indicators are the major impact factors of most heavy metal enrichment. The surface of the soil in city park has been affected by human activities. (5) Pb, Zn, Cu three elements have more significant correlation, more significant relevance between Cr and Ni, Co, Fe three elements, indicating that the sources of Cu, Zn, Pb three elements have a greater similarity, Mn and As, Ni , Co, Fe have significant correlation; Cu and Cr, Mn, As, Ni, Co, Fe less correlation coefficient, indicating the possibility of with the same source is small. At the same time it show that external contaminate source of city park soil is complex.