| This paper is based on the heavy metal geo-chemical characteristic of surface sediment of Baoji Wangjiaya reservoir. By experiment shows the physical and chemical characteristics of surface sediment in this area(pH, conductivity, ignition loss quantity, calcium carbonate, magnetic susceptibility and partical size); Using X-Ray fluorescence spectrometer analysed the levels of main heavy metals in sediments;Revealing the chemical speciation of heavy metals through the BCR four-step sequential extraction method which was modified by the European Economic Community; The sediment partical size composition as well as the heavy metals distribution situation in different partical size sediment was discussed through the screening experiment; Determined the urease of sediment by the phenol-sodium hypochlorite colorimetric method; At last,evaluated the pollution of heavy metals in the sediment of Baoji Wangjiaya reservoir by using the method of geoaccumulation index,nemerow index and potential ecological risk index, these provide a scientific reference for making reasonable use prevention of reservoir resources. The main conclusion of this study are as follows:(1) The average value of pH,conductivity,low-frequencey magnetic susceptibility, high-frequency magnetic susceptibility, frequencey magnetic susceptibility, loss on ignition and calcium carbonate are8.1,315us/cm,87.13×10-8m3/kg,79.32×10-8m3/kg,8.80%,9.39%and140.87g/kg.(2) The average value of As, Co, Cr, Cu, Mn, Ni, Pb, V and Zn of surface sediment in Wangjiaya reservoir is14.73mg/kg,17.98mg/kg,96.15mg/kg,37.81mg/kg,950.5mg/kg,46.65mg/kg,35.01mg/kg,115.3mg/kg,101.9mg/kg. The content of the9kinds of elements were higher than the average values of shaanxi soil background, of which Co, Cu, Mn and V are the highest respectively higher than shaanxi soil background value of1.70,1.77,1.71and1.72times; The Ni and Pb are second respectively higher than shaanxi soil background value of1.62and1.64times; the content of As, Cr and Zn are respectively higher than shaanxi soil background value of1.33,1.54and1.47times; which shows that the heavy metals in sediment of Wangjiaya reservoir have enriched in different degrees. (3) The content distribution characteristics situation of heavy metal in the middle reservoir space is:the middle of the reservoir>the lower of the reservoir> the upper of the reservoir; he distribution situation in the edge of reservoir is:the content of As, Cr, Co, Cu, Mn, Ni and V in left side are more than the right side, Pb and Zn is right side more than the left(4) The morphological of heavy metal in the surface sediment:The element Mn in sediment is given priority to the acid extractable fractionation, the liable state is far greater than its stable state, it illustrate that element Mn is easily released from the sediment, as well as removal and transformed in the water whic effect on water quality largely; Pb, Zn, Ni, Cu, Cr and Co are mainly exist by residual condition, among them the element Cu is very stable, highly reached81.86%.The element Cu and Ni are exist in stable form all over the reservoir by residual state which is not easily released to harm water environment; However the Zn is stable in the middle of the reservoir and liable in the edge of the reservoir relatively; And the Cr is in very contrast compare to Zn; On the whole reservoir the Mn is extremely liable in the acid extractable fractionation, which is very easily released to harm water environment(5) The content distribution of heavy metal in different particle size of Baoji Wangjiaya reservoirsediment roughly divided into three categories:the first kind is the elements of As, Cr, Mn, Pb and V, their characteristic is the mean level in the range of0.063-0.2mm size is the highest and in the small particle size is low; The second kind is Cu, Ni and Zn, their feature is the content in the range of<0.0308mm size is the highest, with the reduction of particle size, the content is gradually increasing; The third kind is Co, their feature is the content in the range of<0.2mm size is the highest, with the decrease of the size, t the content is also gradually reduced.The mean enrichment factor of As, Co, Cr, Mn, Pb and V in each particle size are smaller than2, belong to the mild pollutions level; The element Cu in the range of>0.05mm size are smaller than2, belong to the mild pollution, in the range of<0.05mm size are more than2, belong to the moderate pollution; Ni and Zn in the range of>0.0308mm size are smaller than2, belong to the mild pollutions, in the range of<0.0308mm size are more than2, belong to the moderate pollution(6) The range of urease activity in sediment are between1481.8and8004.2mg/100g.24h, the average is4909.71mg/100g.24h, the minimum appeared in the K1 place, maximum appeared in K8place, the variation coefficient was0.467, The urease activity and Pb, Zn, Cu, As, Co, Cr, Mn, Ni are of positive correlation relationship, and with the Cu, Pb, Co and Cr are reached significantly (P<0.05).Therefore, the heavy metal in the reservoir sediment show a certain stimulation to the urea urease activity, for the content of heavy metal increased in one certain concentration range promoting the urease activity of sediment(7) The evaluation of Accumulation Index shows that:the minimum of As, Co, Cr, Cu, Mn, Ni, Pb, V and Zn are in zero pollution level, and the maximum are in light pollution level, on the whole, As and Zn are in zero pollution level and other elements are in light pollution level, The Accumulation Index order of the heavy metal is:Cu> V> Mn> Co> Pb> Ni> Cr>Zn> As.The evaluation of Nemerow Index shows that:there are certain degree pollution exsit in Baoji Wangjiaya reservoir on the whole, the comprehensive Nemerow Index is2.88, in the moderate pollution condition, among them, the single pollution index of Cu is the highest, and As is the opposite, The Nemerow Index order of the heavy metal is:Cu>V>Mn>Co>Pb>Ni>Cr>Zn>As, this are consistent with the accumulation index evaluation results.The evaluation of Potential Ecological Risk Index shows that:the range of comprehensive Risk Index is between38.4and74.26, the average is58.27, in the moderate pollution degree; Among them, the Potential Eecological Risk of As is the biggest and Zn is the opposite; The Potential Ecological Risk Index order of the heavy metal is:As>Cu>Co>Pb>Ni>V>Mn>Cr>Zn. |
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