| The lakes in Xi’an have a positive role in inheriting ancient capital culture,regulating urban climate,building urban landscape and creating suitable environment.However,the pollution of water environment quality and heavy metals are becoming more and more serious,with the development urbanization and lakes have characteristics of poor mobility and week self-purification ability.It hindered the perfection of urban function and the improvement of living standard.It has attracted extensive attention from all circles of society.Accordingly,it is significant to study water environment quality,heavy metal content distribution and pollution status of main lakes in Xi’an City.In this paper,the five lakes(Qujiang Pool,Taiye Pool,Xingqing Lake,Guangyun Pool,Weiyang Lake)in Xi’an as the research object.The content and distribution of water quality indications(pH、DO、COD、BOD5、NH3-N、TN、TP)in water and heavy metals indicators(Cu、Zn、Pb、C、Cd、Mn、Ni)in water and surface sediments were analyzed.The water environment quality of lakes in Xi’an were evaluated from 3 aspects of water quality assessment,eutrophication assessment and heavy metals assessment,and the heavy metals in lake surface sediments was evaluated.The results are as follows:(1)There were differences concentrations of hydrochemical indicators between the five lakes and sites within lake.The pH values of the five lakes ranged from 5 to 8.Transparency ranged from 5.0 to 26.3 NTU.DO ranged from 8.12 to 13.21mg/L.These indexes of the five lakes were higher than the class Ⅳ of the surface water environmental quality standard.COD ranged from 5.50 to 94.90 mg/L.Only the COD of Guangyun Pool was lower than the class Ⅳ of the surface water environmental quality standard.Its average value was 16.55 mg/L.COD5 ranged from 3.69 to 6.46 mg/L.NH3-N ranged from 0.34 to 1.10 mg/L.The two index of the five lakes was lower than the class IV of the surface water environmental quality standard.TN ranged from 0.48 to 1.92mg/L.Only the TN of Guangyun Pool was lower than the class IV of the surface water environmental quality standard.Its average value was 1.83 mg/L.TP ranged from 0.08 to 0.1 lmg/L.Only the TP of Guangyun Pool and Xingqing Hu were lower than the class Ⅳ of the surface water environmental quality standard.Its average value was 1.83 mg/L.(2)The heavy metals contents in water and surface sediments showed different distribution in different regions.The key pollutant of heavy metals in water was Pb.The coefficients of variation of Pb in five lakes were between 2.983 and 15.837,which indicated that the fluctuation is small between sampling points.The average content of Pb ranking:Weiyang Lake>Guangyun Pool>Taiye Pool>Qujiang Pool>Xingqing Lake.The contents of Cr,Cd and Ni in water were not significant difference between the five lakes.The content of Zn was quite prominent between the five lakes and the contents of Cu,Pb and Mn was extremely significant difference between the five lakes.The key pollutant of heavy metals in Surface sediments was Cd.The coefficient of variation of Cd in five lakes was between 45.935 and 255.665,which indicated that the fluctuation is large between sampling points.The average content of Cd ranking:Xingqing Lake>Guangyun Pool>Weiyang Lakel>Qujiang Pool>Taiye Pool.The contents of Zn,Pb,Cd and Ni in water were not significant difference between the five lakes.The contents of Cu,Cr and Mn were extremely significant difference between the five lakes.Overall,the correlation between heavy metals in water and sediment was not strong.(3)The results of water quality by the single factor evaluation method and synthetical index method were basically consistent.The results of analysis by the single factor evaluation method were that the water qualitys of the five lakes belong to worse than grade V.The results of analysis by the synthetical index method were that Guangyun Pool,Qujiang Pool,Xingqing Lake and Weiyang Lake belong to severe pollution,and Taiye Pool belongs to heavy pollution.These two methods all showed that the main contamination index of Qujiang Pool were pH value,COD,Pb,and Cd.The main contamination index of Taiye Pool and Xingqing Lake were COD,TP,and Pb.The main contamination index of Guangyun Pool was pH value,TN,TP,Pb.The main contamination indexes of Weiyang Lake were COD,Pb.The result of eutrophication by universal index method was that the eutrophication of the five lakes belongs to level 7 eutrophication.Eutrophication ranking:Xingqing Lake>Weiyang Lake>Guangyun Pool>Qujiang Pool>Taiye Pool.The results of single factor index showed that Cu,Zn,Cr and Cd in the five lakes were no polluted,Pb pollution was serious,and the five lakes were heavily polluted.The Nemero comprehensive pollution index showed that heavy metals in the five lakes water belong to heavy pollution,and pollution index ranking:Weiyang Lake>Guangyun Pool>Taiye Pool>Qujing Pool>Xingqing Lake.(4)The results of analysis by geoaccumulation index method,single pollution factor of potential ecological risk index method and enrichment factor method and nemerow index method were basically consistent.The results of analysis by geoaccumulation index were that the main pollution factors in surface sediments of the five lakes is Cd.Cd in Qujing Pool and Taiye Lake belong to slight pollution.Cd in Guangyutan and Weiyang Lake belong to medium pollution.Cd in Xingqing Lake belongs to heavy pollution.The results of analysis by single pollution factor were that Cu,Zn,Cr,Pb,Mn,Ni in the water of five lakes belong to no pollution,the pollution of Cd is serious,and the five lakes belong to heavy pollution.The results of enrichment factor method were that Cd pollution is the most serious in the five lakes,Cd in Qujiang Pool,Gungyuntan and Weiyang Lake belong to stronger pollution,Cd inTaiye Pool belong to strong pollution,and Cd in Xingqing Lake belong to extremely strong pollution.In addition,Cr,Ni in Qujiang Pool had slight pollution,Pb,Zn had Moderate pollution.Zn in Taiye Pool had slight pollution.Zn,Pb in Xingqing Lake and Weiyang Lake had slight pollution.Pb,Zn in Guangyun Pool had Moderate pollution.(5)The results of analysis by nemerow index method were that Taiye Pool belongs to mild contamination.Qujiang Pool,Guangyun Pool and Weiyang Lake belong to middle level pollution.Xingqing Lake belongs to heavy pollution.(6)The result of analysis by potential ecological risk index method were that Cu,Zn,Pb,Cr,Mn,Ni in the surface sediments of the five lakes belong to light ecological harm(level 1),and Cd in the surface sediments of the five lakes have ecological harm.Cd in Taiye Pool belongs to medium ecological harm(level 2).Cd in QujingPool,Guangyun Pool and Weiyang Lake belong to strong ecological harm(level 3).Cd in Xingqing Lake belongs to extremely strong ecological harm(level 5).From integrated potential ecological risk index of heavy metals,Qujiang Pool,Taiye Pool,Guangyun Pool,Weiyang Lake belong to light ecological harm(level 1),and Xingqing Lake belong to strong ecological harm(level 3).(7)Pollution sources of Cu,Cr,Mn may be source naturals and pollution sources of Pb,Zn,Ni and Cd may be anthropogenic sources in Qujiang Pool.Pollution sources of Zn and Mn may be source naturals and pollution sources of Cd,Ni,Cu,Cr and Pb may be anthropogenic sources in Qujiang Pool.Pollution source of Cu and Zn may be source natural,and pollution sources of the other heavy metals may be anthropogenic sources in Xingqing Lake.Pollution sources of Cr may be source naturals and pollution sources of the other heavy metals may be anthropogenic sources in Guangyun Pool.Pollution sources of Mn and Ni may be source naturals and pollution sources of Cu,Pb,Cd,Cr,and Zn may be anthropogenic sources in Weiyang Lake. |
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