| The riparian zone is in the amphibious staggered zone of transition in Weihe River,which not only protects the water quality from pollution,but also bears the pressure of production and living in Shaanxi Province,so heavy metal pollution in its riparian soil has aroused strong concern.The study area was selected Weihe River riparian zones in Shaanxi province,and heavy metals in riparian soils were studied as the research object.The soil samples were collected from 11 sampling sections,and the distribution of each section was as the center of the river,extended to the north and south direction by different buffer zones of 100m,300m,500m,800m,1000m,2000m and 3000m.The study determined the content of heavy metals in soils(As?Cr?Cu?Ni?Pb?Zn)and other soil physical and chemical properties,including soil organic content,soil particle composition,soil pH,and analyzed the statistical characteristics of soil physical and chemical properties;then by these means of correlation analysis,cluster analysis and GIS trend analysis,the distribution characteristics,influencing factors and pollution sources of heavy metal pollution in riparian zone soils of Weihe River were studied;finally,using single factor pollution index(Pi),Nemerow index(P),geoaccumulation index(IGeo)and Hakanson Potential Ecological Risk Index(RI)comparatively evaluated for soil heavy metal pollution level in the study area soils.The main conclusions were as follows:(1)All of the elements As,Cr,Cu,Ni,Pb,Zn had a certain pollution to riparian zone soils in Weihe River,where was low organic matter content,dominated by the sand and weak alkaline in study area.The variation range of contents of the elements As,Cr,Cu,Ni,Pb,Zn in Weihe River riparian zone soils were 3.00-18.45 mg·kg-1,51.65?114.05 mg·kg-1,9.10?59.15 mg·kg-1,12.35?44.30 mg·kg-1,16.70?119.75 mg·kg-1,29.35?204.60 mg·kg-1 respectively,and the mean value were 10.90 mg·kg-1,77.33 mg·kg-1,25.79 mg·kg-1,29.07 mg·kg-1,29.85 mg·kg-1,75.89 mg·kg-1 respectively,which were higher than background values in Shaanxi Province soil.The variation range of the content of organic matter in Weihe River riparian zone soils was 1.56?80.97 g·kg-1,the mean value was 15.12 g·kg-1.From the average percent of different particle sizes,the percentage of clay is 6.26%,the silt accounting for 38.93%and the sand accounting for 54.80%.The variation range of pH in Weihe River riparian zone soils was7.06-9.18,the mean value was 7.94.(2)The spatial distribution characteristics of heavy metals in Weihe River riparian zone soils were analyzed according to different sampling methods:?From the different sampling sections,the contents of heavy metal elements Cr,Cu,Pb were higher than background values in Shaanxi Province soils in the 11 sampling sections;However,the contents of heavy metal elements As,Ni,Zn were slightly lower than background values in Shaanxi Province soils in#6?#8 sampling sections,other sampling sections were higher than the background values.As a whole,the content of heavy metals in Weihe River riparian zone soils decreased along the direction of the water flow;through detailed analysis,the content of heavy metals in soils firstly decreased and then increased,but the extent of decrease was greater than the extent of increase,in addition to the element cr almost unchanged.?From the different buffer zones,the content of heavy metals in the most recent buffer zone(0?100m)soils was lower than background values in Shaanxi Province soils,except for the elements Cr and Pb;With the increase of the distance from the riparian zone,that is,the more the buffer zone increased(100-1000m),the more the content of heavy metals in soils increased,which of all were higher than background values in soils;In some certain buffer zones(1000?3000m)of the riparian zone,the content of heavy metals in soils decreased or remained constantly with the increases of distance,which was still higher than background values in soils.?From the different buffer zones on the different sampling sections,in sections of Baoji(#1?3),the content of the six elements in soils decreased,especially the lowest content of heavy metals in near riparian zones in study area,however the highest content in the most far buffer zone(3000m),in addition to that the highest content of the elements Pb,Zn in the 1000m buffer zone.In sections of Xi Xian(#4?7),this area belonged to the region of the lowest of heavy metal content in study area,especially the sampling section#6(located in Xi'an Caotan Road eight)presented particularly low value,mainly affected by the sampling environment;and the highest content of heavy metal was in the 1000m buffer zone.In sections of Weinan(#8-11),the highest content of heavy metals was distributed in near riparian zones(500m)in study area,especially in water-level-fluctuating zone close to the river;and the content of heavy metal in other areas in soils changed little.(3)Through correlation analysis and cluster analysis for 6 kinds of heavy metals in soils and other physicochemical properties,and influence factors,As,Cr and Ni,Pb,Cu and Zn showed strong correlation,indicating these elements exist geochemical characteristics in common,if they were in the same or similar external conditions,the trend of changes was consistent;and these elements came from the same sources of pollution,and soils in study area may exhibit complex pollution.The contents of heavy metal of the six elements(As,Cr,Cu,Ni,Pb,Zn)in soils and organic matter,clay and silt in soils showed positive correlation,however,which showed a negative correlation with soil pH,sand in soils.In the selected influence factors,the elevation factor and elements As,Cu,Ni,Pb,Zn showed a strong positive correlation,but almost no correlation with the element Cr;the slope factor,vegetation coverage(represented by NDVI value)showed a weak correlation with the contents of heavy metal of the six elements(As,Cr,Cu,Ni,Pb,Zn)in soils;The proportion of different land use types in the different buffer zones on the different sampling sections showed strong correlation with the contents of heavy metal of the elements As,Cu,Ni,Pb,Zn,but showed very weak correlation with Cr.(4)By single factor pollution index(Pi),Nemerow index(P),geoaccumulation index(IGeo)and Hakanson Potential Ecological Risk Index(RI)evaluated for soil heavy metal pollution level in riparian zone soils of Weihe River,compared to which method was more valuable in study area.? evaluation of heavy metal pollution on different sampling sections:Accumulation index values of the six elements were decreased along the river flows from the#1?#11 sections,and had a fluctuation rule in a certain region,among which the elements Pb is the highest level of pollution in study area.The variation range of potential ecological risk index(RI)was 26.83?38.10,which were slightly polluted.The pollution level of heavy metals in the riparian zone soils of Weihe River showed slight pollution from upstream to downstream,and the pollution degree was reduced along the river flows.?evaluation of heavy metal pollution in different buffer zones:Accumulation index values of the six elements were increased away from the river,and had a highest peak in 100m,500m,1000m;especially accumulation index values of the element Pb with a most extent increased,presented medium pollution level in the buffer zone of 1000m,which polluted widely.The variation range of potential ecological risk index(RI)was 26.35?38.93,which were slightly polluted;the change trends of RI were:increased within buffer zones(1000m),decreased or unchanged away from buffer zones(1000m?3000m). |
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