The Heavy Metal Pollution And Risk Assesment Of Soil In Manas Lake Wetland

In this paper,the wetland area of Manas Lake was divided into three functional zones:Zone A（entrance to lake）,Zone B（cultivation returned zone）and Zone C（restoration zone）.Eight kinds of heavy metals in soil,such as Zn,Cu,Mn,Ni,Cr,Hg,As and Pb,were studied.A total of 60 samples were selected to collect soil samples and 120 soil samples were collected for determination.The soil physical and chemical properties and the pollution status of heavy metals in the study area were preliminarily understood by Land Statistics Method.The soil pollution status and spatial differentiation law in the study area were further analyzed by GIS and other related means.The correlation between heavy metals was studied by Pearson Correlation Analysis Method,and the soil in the study area was explored by a variety of Relevant Pollution Assessment Method.Soil Pollution and Potential Ecological Hazard Level,and Principal Component Analysis and Cluster Analysis methods were used to determine the main pollution sources in the region.The following conclusions are drawn:（1）The soil of manas lake is alkaline,and the average p H value of the soil is>in zone A,>in zone B,and>in zone C.On the whole,the content of organic matter in area C was the highest and most concentrated,and its content also increased with the deepening of soil layer.Area B is concentrated in 0～20cm,and its variation coefficient increases with the deepening of soil layer.The difference of salt content between 0～20cm and 20～40cm is very significant,and the surface layer is more than20～40cm.Under different soil layers,the salt content is shown as>in zone A,>in zone B,and>in zone A,respectively.The soil water content in some areas shows A high accumulation state,which is sequentially arranged as>zone A,>zone B in zone C.The two regions A and C are not only larger in content than zone B,but also have A greater coefficient of variation than zone B.（2）The extreme values of heavy metals in three zones of A,B and C are quite different,and the contents of different heavy metals are also quite different,and the range of variation is also quite different.The content ranges of Cr,Cu,Mn,Ni,Pb,Zn,As and Hg are 29.10 mg/kg to 33.02 mg/kg,68.84 to 91.87 mg/kg,340.82 to 413.19mg/kg,10.49 to 14.29 mg/kg,5.22 to 7.42 mg/kg,30.82 to 52.47 mg/kg,114.22 to128.14 mg/kg and 0.05 to 0.07 mg/kg,respectively.Among them,the variation range of Mn content is the largest and the mean value is the highest,and the mean value of Hg is the smallest but the variation range is larger.The order of heavy metal content is Mn>As>Cu>Zn>Cr>Ni>Pb>Hg.The correlation analysis between heavy metals and physical and chemical properties shows that the elements of Cr,Cu,Mn,Pb has significant negative correlation with total salt（p<0.05）,which shows that with the increase of total salt,Mn shows a downward trend.The negative correlation between Ni and Zn without total salt is significant（p<0.01）.（3）According to the distribution characteristics of heavy metals in Manas Lake,the high values of Zn,Cr,Pb,Ni and Hg in Zone A are mainly distributed near the salt field,while the low values are near the entrance to lake,showing a decreasing-to-increasing trend from southeast to northwest.The elements of Mn,Pb,Zn and Hg elements in Zone B show an increasing trend from southwest to northwest and northeast.It is considered that the pollution sources of these four elements are related to natural environment and industrial production.On the whole,Zone C shows a trend of increasing gradually from north to south.The high value mainly distributes near the industrial oil extraction base,and then gradually weakens outward.It can be concluded that the pollution of these five elements is affected by human factors at the same time,but the influence of natural factors is not obvious.（4）Pearson correlation coefficient shows that there is a very significant positive correlation between Pb and other heavy metal elements（p<0.01）.The highest correlation coefficient is found between Pb and Zn（r=0.801,P<0.01）.There is a significant positive correlation between Cr,Zn,Mn and Ni（p<0.01）.There is a significant correlation between Cr and Mn,Ni and AS（p<0.05）.There is a significant correlation between elements.Through principal component analysis,it is concluded that Cr,Cu,Mn,Ni and Zn have the largest load value,which does not exceed the background value of Xinjiang,and their sources are similar,so it is clear that they are polluted by natural factors;The second principal component shows that the load value of As element is the largest,while the third principal component shows that the load value of Zn element is the largest,indicating that the pollution source of Zn is different from other seven heavy metal elements.（5）According to the results of pollution assessment of Manas Lake,the pollution degree of different heavy metals is quite different,especially for As,Hg and Cu.The average values of As and Hg are between 10.19-11.44 and 2.5-3.5,respectively,while that of Cu is between 3-3.44,which is moderately and severely pollution.The pollution of Zn,Ni and Pb in the three zones is slight.The total pollution levels of Cr and Mn are relatively low,their values are 0.87～1.08 and 0.65～1.01,respectively.It is considered that they are affected by natural factors such as precipitation and atmosphere.Pollution load index grading shows that the order of pollution in A,B and C zones is Zone C>Zone B>Zone A,and belong to moderate pollution.The reason is that zone C is near the oil extraction base.Because the oil extraction and refine processes pollute the soil of the study area to a certain extent,the discharge of industrial wastewater also leads to the accumulation of heavy metals in the soil,resulting in the pollution load of Zone C far higher than that of Zone A and Zone B.H_RI is 161.67,273.68 and 238.36 in A,B and C,respectively,reaching moderate strength level.