Heavy Metal Contamination,distribution And Source Identification In Lake Sediments From The Badain Jaran Desert,NW China

In recent years,high concentrations of heavy metals in different natural systems have become a global problem.Heavy metals can be deposited or even transported away from sources of heavy metal emissions by long-distance transportation,thereby causing complex and extensive heavy metal pollution in the environment.Still and all,evidence of heavy metal pollution in remote areas far from the emission sources is slightly insufficient.Desert hinterland with less human activity is more sensitive to changes in heavy metal content.It is an ideal area to study the impact of human activities on remote areas.About 110 runoff-free lakes in the Badain Jaran Desert and its surface sediment is a good carrier for studying the concentration of heavy metals in the desert hinterland.Discussing the heavy metal pollution in the surface sediments of lakes in the Badain Jaran Desert not only helps us to assess the impact of human activities on the ecological environment,but also provides new evidence for the study of the earth surface system element migration and transformation laws and geochemical cycles.In this study,171 samples and 24 water samples were collected in the Badain Jaran Desert.Among them,sediment samples include 67 desert eolian sand samples,a total of 99 surface sediment samples from 5 lakes,and 5 atmospheric dust samples.And 4eolian sand samples and 8 lake surface sediment samples were divided into samples with different particle size ranges,includ>250?m,250-125?m,<125?m,>125?m,125-63?m and 63?m,Water samples include 11 lake waters,12 groundwater and 1 rainwater sample.Firstly,test the content of Cr,Cd,Ni,Zn,Pb,Cu in the above samples by ICP-MS.Secondly,the background values of heavy metal content in the aeolian sand soil of Badain Jaran Desert were determined by the cumulative distribution frequency function?CDF?.Then,the content characteristics and spatial distribution of heavy metals in the surface sediments of these five lakes were analyzed,and the pollution load index?PLI?and the geoaccumulation index(I_geo)were used as evaluation criteria to identify polluted heavy metals and evaluate the lake of pollution.Finally,heavy metal elements in the samples of lake surface sediments and were compared with it in the samples of eolian sand,atmospheric dust,water body and the soil of the adjacent desert.Then,combining with correlation analysis and spatial distribution of the content revealed that the relationship between the content of heavy metal elements in lake surface sediments with total organic carbon?TOC?and grain size.We have initially clarified the status of heavy metal pollution and sources of heavy metal in the surface sediments of lakes in Badain Jaran Desert.The results suggsered that:?1?The background values of the heavy metal contents of Cr,Cd,Ni,Cu,Zn,and Pb in the eolian sand of the Badain Jaran Desert were 42.74ppm,0.21 ppm,28.62 ppm,21.78 ppm,45.29 ppm,and 17.54 ppm,respectively.The background value of Cr was less than the world average Cr content.The background value of Cd was greater than the soil background value of the Mengxin Plateau Lake District of China and the mountain lake region of Northeast China Plain,and was close to the world average element concentration.The background values of Ni,Cu,and Zn elements were much smaller than the world average element concentration;the Pb element content was relatively close to the world average element concentration.?2?The concentration of Cr and Cd in surface sediments of lakes in the Badain Jaran Desert was higher than the corresponding background value,while the content of Ni,Cu,Zn and Pb were lower than the background value of heavy metals in this area.The content of heavy metal elements in desert lake water was higher than that in groundwater.?3?The I_geo index indicated that the pollution degree of Cr was mainly unpolluted-moderately polluted,Cd was moderately polluted,and that of Ni,Cu,Zn and Pb were not polluted.As far as 5 lakes were concerned,the PLI indexs of the Baoritaolegai Lake and Sumubarunjaran Lake in the southeast of this desert hinterland were 1.30 and 1.23,respectively.And the PLI indexs of the Yindeer Lake,Zhunsangenjaran Lake and Tosenjaran Lake in the desert hinterland were 1.22,1.05 and 0.97,respectively.?4?The spatial distribution of contaminated heavy metals in the lakes showed the following characteristics:the contaminated heavy metals were in the same lake,and the spatial distribution of the element content characteristics of Cr and Cd was consistent,in addition,the particle size component was in the component content of 250-125?m It also had consistency with the heavy metal element content of both.In different lakes,the distribution characteristics of heavy metal content and different particle size components were different.The Cr and Cd characteristics in the spatial distribution of the desert showed the following:The Cr element content in the southwest of the desert was significantly higher than the element concentration in the desert hinterland,and the southwest area of the desert was adjacent to the Hexi Corridor area.In addition,the spatial distribution of the content of particle size components less than 125?m was more consistent with the spatial distribution of Cr content;the element content of Cd was more uniformly distributed in the desert,and there was no obvious high value area,but the Cd content was in the desert lake It was relatively low in the range of about 3-8km.We reached these conclusions in our study:?1?The higher background values of heavy metals such as Cd and Cr occurred in the Badain Jaran desert,moreover,the background value of Cd was closed to average element concentration of the world.?2?In the Badain Jaran desert,surface sediments in lakes were mainly polluted by heavy metals of Cr and Cd.The pollution degrees of Cr and Cd were unpolluted to medium pollution and medium pollution relatively,while Ni,Zn,Cu and Pb have little pollution in this area.?3?The eolian sand surrounded in the desert could be carried into the surface sediment of lakes,which had a great contribution for the heavy metal pollution in this desert.Moreover,heavy metals of Cr in the eolian sand was affected by nearby human activities and remote pollutions,whereas Cd was mainly transported to the Badain Jaran Desert through atmospheric circulation and deposited in the eolian sands.?4?The fine particles in the desert could be carried by the wind.The Badain Jaran Desert with a higher background values could serve as a source of dust and result in a heavy pollution in other regions.Which was related that the heavy metals elements adsorbed in the fine particles could be transported to other regions by atmospheric circulation.