Soil Quality And Its Assessment In Green Areas Of Chongwen District Of Beijing

The urban green area functions exertive can not be separated from the soil. The urban residential environmental suitability, environment quality and people's life quality are closely related to urban soil functions. In this study, soil samples from four types of urban green areas in Chongwen District of Beijing, including park green area, settlement green area, roadside green area and street tree greenbelt, were collected. And soil physical and chemical properties, heavy metal pollution level, as well as microorganism quantity and activeness were determined. The main problems of green areas soil of Chongwen District were revealed. Fertility quality, environment quality and biological quality of green areas soil were evaluated. The research demonstrated:(1) Soil physical and chemical properties of urban green areas in Chongwen districtFour types of urban green areas soil in Chongwen District are sandy soils. The amplitude of Chongwen District green areas soil bulk density is 1.12~1.69 g/cm3, and average value is 1.35 g/cm3.The bulk density of street tree greenbelt is significantly higher than the other three types of green areas, but the compaction degree not yet reached the level of impact on plant growth. The average value of Chongwen District green areas soil total porosity is 49.14%; Soil total porosity of park green area, settlement green area, and roadside green area is in suitable scope (generally, suitable scope of soil total porosity for plant growth is 50~56%). Only soil total porosity of street tree greenbelt is low (40.95%), which is possibly has certain influence on growth of plant root. The compaction of Chongwen District green areas soil is lower than 2.5Mpa; In general case, growth of plant root will be limited when the soil compaction reaching 2.5Mpa. Therefore, the result of soil compaction shows that there is no obvious soil compaction problem.The amplitude of Chongwen District green areas soil pH is 7.73~8.58. Almost all the soil samples are alkaline. The average value of organic matter, total nitrogen, total phosphorus, and total potassium content is 18.79 g/kg, 0.91 g/kg, 0.96 g/kg and 17.07 g/kg, respectively. The average content of available nitrogen, available phosphorus and available potassium is 50.66 mg/kg, 29.91mg/kg and 44.16mg/kg, respectively. The soil C/N of Chongwen District green areas is 13.03. According to soil fertility standard of the second national soil survey, the soil organic matter content of Chongwen District green areas is in the medium level. Some of street tree greenbelt soil samples'organic matter content is low. The soil total nitrogen content of Chongwen District green areas is in lower-middle level. But the soil available nitrogen content is in low or very low level. The Chongwen District green areas soil does not lack the phosphorus grossly, moreover the total phosphorus content is generally high, and available phosphorus is not the main limited factor in Chongwen District green areas soil. Among the four types green areas soil, settlement green area soil total phosphorus and available phosphorus content is highest. About one-third street tree greenbelt soil samples lack total potassium. The other three types green areas soil do not have the problem. But available potassium has the varying degree lacking in four type of green areas soil. The street tree greenbelt soil available potassium is the most serious lacking.The result of soil fertility comprehensive index shows that the park green area soil nutrient reaches the medium level. The settlement green area, roadside green area and street tree greenbelt soil nutrient is in low level. It is maybe because that available nitrogen and available potassium are low.(2) Soil envioronmental quality of urban green areas in Chongwen districtThe average concentration of Zn, Cu, Pb, Cr, Ni and As in the green areas of Chongwen District is 63.78, 53.72, 46.53, 25.80, 15.76 and 11.74 mg/kg, respectively. According to BVB, BVC, NSEQS-Ⅰo r NSEQS-Ⅱ, the green area soil of Chongwen District is unpolluted by As and Ni, but As, Cu, Pb, Zn is over standard in different degree.Among the four types of green areas, the average concentrations of Zn, Pb and Cr in the soils of the street tree greenbelts are the highest. Cu concentrations in the soils of the settlement green area are the highest, and its Pb concentrations are the lowest. In general, the concentrations of heavy metals in the soils of park green area are lower than those of the other types of green areas.(3) Soil biological quality of urban green areas in Chongwen districtThe average enzyme activity of urease (UA), dehydrogenase (DHA), catalase (CA), acid phosphatase (acid-Pa) and alkaline phosphatase (alk-Pa) in the green areas of Chongwen District is 0.63 mg NH3-N·g-1·24h-1, 92.06 mg TPF·kg-1·h-1, 10.48 ml KMnO4·g-120min-1, 29.02 mg C6H5NO3·kg-1·h-1, and 30.28 mg C6H5NO3·kg-1·h-1, respectively. There are varying degrees of relevance among different soil enzymes as well as soil enzyme activities with soil physico-chemical properties. On the whole, soil enzyme activities in park green areas are the highest, soil enzyme activities in street tree greenbelts are the lowest. No significant differences are found in soil enzyme activities between settlement and roadside green areas. Among the five kinds of soil enzymes, catalase, urease and alkalinity phosphatase are suitable for soil quality enzymatic assessment in urban green areas.The average concentration of soil microbial biomass carbon and soil microbial biomass nitrogen of green areas in Chongwen District is 417.14 mg/kg and 62.86 mg/kg, respectively. The soil basal respiration rate is 0.480 mg CO2-C·kg-1·h-1 in average. The average values of soil microbial quotient and metabolic quotient is 4.09 % and 1.53 mg·g-1·h-1. The total number of microbes (bacteria, fungi and actinomycete) is 4.69×106 CFU·g-1, among which, the proportion of bacteria reached 88.87%. A poor correlation between BR (soil basal respiration), Cmic: Nmic (soil microbial biomass carbon nitrogen ratio) and other soil microbial indicators are demonstrated in this study. In addition, almost anyone microbial indicator is significantly related with another microbial indicator. Soil microbial indicators are significantly with most physical indicator and are significantly correlated with a portion of chemical parameters and heavy metal elements. In all microbial indicators, the number of soil micrbes, Cmic (soil microbial biomass carbon) and Nmic (soil microbial biomass nitrogen) are best suitable for evaluating soil quality.(4) The results of variance analysis and multiple comparisons of all parameters are compared, but significant difference of overall quality condition among four kind of green area soil does been determined, only a general trend can be summed up as follows: the soil quality of park green area is superior to roadside and settlement green area and they all are better than the street tree green area. However, we can get the comprehensive principal component values of all sampling points through the principal component analyzes (PCA), thus having a quantitatively and comprehensively soil quality evaluation to all sampling points. This method not only may carry on sorting to soil quality of all investigation sampling point, but also clearly explain that the quality decrease in order of park green area>roadside green area>settlement green area>street tree greenbelt. And there is significant difference between every two types. In addition, this article applied"digital globe"the software to the urban green area soil sampling program, may be used for reference to the study of urban soil sampling survey.At present, soil quality evaluation system (such as the evaluation principles, methods, indicators, quality standards) of the urban green areas as well as the green areas management system which is closely related with this not yet been established, this article has also conducted the exploring research on the synthetic evaluation of urban green areas soil quality, and above-mentioned related issues were discussed with a clear viewpoint of the author. The author believed that the suitable scale of green area soil quality assessment study should be block-scale level, this research criterion not only matched with afforested construction, green areas management practice criterion, also avoided high degree of heterogeneity problem of urban soil in larger-scale studies on urban soil quality. Therefore, development trend of urban green areas soil research are soil quality monitoring and evaluation which facing urban soil management and healthy living environment. And research-scale will be reduced to the plots level which matching with the building or land management activities.