Soil Metal Contamination, Microflora And Enzyme Activities Of Different Land Use Types In The Lead/Zinc Mine Tailing Dam Collapse Area(Sidi Village,in Yangsuo, Of Guangxi, China)

Mining activity is a chief source of metals entering into the environment. In the process of mining exploitation and ore concentrating, mine tailing and wastewaters are created. This results in the surrounding environment being severely polluted. The most serious problem is that of spilled mine tailing. In1970s, the collapse of the tailing dam in Sidi village lead/zinc mine (Yangshuo, Guangxi Zhuang Autonomous Region, SW China) led to the spread of mining waste spills on the farmland.The objectives of this study are to:(1) understand the relationship between heavy metal contamination and soil properties in different land use types around the pollution area.(2) reveal the effect of heavy metal contamination on soil microbial community and enzyme activities.In this paper, the impact of lead/zinc mine tailing dam incident on the degree of environmental response to soil properties, soil microbial ecological characteristics and enzyme activities in different land use types were investigated using field investigations.12,12and9soil samples for paddy fields, maize fields and citrus orchards were respectively taken from surface layer (0-20cm). In the laboratory, a part of the soil samples after air-drying at room temperature, were sieved with nylon mesh(0.15mm) for some soil characteristics parameters, heavy metals such as Pb、Zn、Cu、Cd analysis; a part of the fresh soil samples (the moisture content is about40%) for some sensitive microbial ecological indexes and kinetic enzyme activities measured. The main results of this study are presented:Canonical correspondence analysis (CCA) was applied to reveal the relationships between soil properties and heavy metal pollution in different land use types. The results show that the DTPA-Pb, DTPA-Cd, DTPA-Zn and total Zn are the main pollution in the first axis and second axis in CCA analysis, which prove that the Pb/Zn/Cd mine of the tailing sand is a multi-mineral orebody. Moreover, from the arrow distribution of heavy metals, it can be seen the maximum content of heavy metal pollutant appeared in the paddy fields. The mean value of total Pb, total Zn, total Cu and total Cd in paddy fields are1132.31mg/kg,1829.17mg/kg,130.21mg/kg and45.47mg/kg respectively and have the14.16、9.15、2.61、151.57times more than the environmental quality evaluation standards for farmland of edible agricultural products of China (HJ/T332-2006), which indicates this area should not be as rice-land anymore.The point of SOC, TN and heavy metal arrows in the same quadrant of CCA bioplot shows that they have the positive correlation relationship. Moreover, the SOC content in paddy fields, maize fields and citrus orchards are13.72g/kg,14.43g/kg and18.14g/kg respectively; the TN content in paddy fields, maize fields and citrus orchards are0.70g/kg,0.65g/kg and0.86g/kg respectively. The SOC and TN content are relatively high in paddy fields which has the significant statistical differences with maize fields and citrus orchards. Furthermore, CCA shows that AN and C/N have high correlation, and good correlation exists among heavy metals, AN, C/N and CEC. In comparison with other soil characteristic parameters, AP, AK should be given more consideration to the fertilization and human active intensity. The pH value is mainly related to the karst area soil parent material.By adopting Biolog method combining with principal component analysis, it was found that as compared with the maize fields and citrus orchards, the average well color development(AWCD), diversity index, eveness index and dominance index of microbial community were all significantly lower in the paddy fields. The metabolic characteristics of different soil microbial communities varied significantly among different land use type, and the variation was mainly manifested in the metabolic patterns of carbon sources such as carbohydrates, carboxylic acid and amino acids. Long term heavy metal pollution may adversely affect the structure of communities, the number of soil bacteria, actinomyce and fungi in paddy fields decreased greatly compared with maize fields and citrus orchards, but the fungi/bacteria was on the contrary. In heavily polluted paddy soils, the ability of soil microbes in utilizing the carbon sources was inhibited, which appeared to increase the accumulation of organic matter and total nitrogen. Total soil enzyme activity index (Et) was proposed which is a dimensionless parameter and could be calculated from monitoring enzyme activity in soil samples. Et in paddy fields, maize fields and citrus orchards are4.345,5.153and5.502respectively. The result showed that the enzyme activity is largest in the maize fields and is smallest in the paddy fields. It is not only because of the paddy fields are polluted by heavy metals seriously, but also related with the maize cultivation, maize can effectively alleviated toxicity of soil heavy metal pollutants.Path analysis showed that soil available Pb, Zn and Cd directly inhibited the activity of soil saccharase, acid phosphatase and urease and the soil available Zn directly stimulated activity of soil protease. Soil AN directly affected the soil activity of soil urease and cellulase, soil AK directly affected the soil activity of saccharase and protease. The above results demonstrated that because of the complicated ad uncertain relationships between the contents of soil Pb, Zn, Cu and Cd and the activities of the test enzyme activities, it shouled be cautious to use the indicate soil heavy metals pollution.