| Yangling-Xingping Section of Wei River Located the Middle reaches of Shaanxi, which is an important industrial and agricultural town . In recent years, With the development of economic, resources and geographical advantages about Wei River are shown more and more prominent. Because of increasing the degree of environmental protection, many high-polluting and high energy-consuming enterprises move from the bigger cities to the smaller ones, such as Yangling,Wugong,Xingping and increase the environment pressure of these Region. This article collected 9 Sampling profile of surface mixed sediments, By experiment shows the physical and chemical characteristics of surface sediments, using X-Ray Fluorescence Spectrometer analyse the levels of main heavy metals in the sediments, making use of a modified four-step BCR sequential extraction method reveals the chemical speciation of heavy metals, adopting mechanical sieving experiments study the size component and the diversity of heavy metals enrichment and morphological characteristics in different size sediments. Discussing the relationship about the physical and chemical indicators, heavy metal concentration levels and the chemical speciation.These provided a scientific basis for making use of resources and targeted treatment pollution about Wei River. The main conclusions of this study are as follows:(1) Physical and chemical indicators of Yangling-Xingping section in the surface sediments are that, the average of pH value, conductivity, loss on ignition,_low-frequency magnetic susceptibility, high-frequency magnetic susceptibility and frequency magnetic susceptibility are 7.972,404μs/cm, 60.7×10-8m3/kg,59.3×10-8m3/kg and 2.45%. The results of size analysis show that the main compositions of sediments are silt and sand. Constant element is consistent with crustal abundance. This shows that the river sediments are derived from the weathering of crustal rocks and reflects the original mineral composition of the crust.(2) The average content of heavy metals, such as Cu, Pb, Zn,Cr, Ni,Co and Mn are 17.7 mg/kg, 18.9 mg/kg,72.7 mg/kg,100.2 mg/kg,21.1 mg/kg,,33.9 mg/kg and 484 mg/kg. Where Cr, Co and Zn were significantly exceed the mean soil background value in Shaanxi Province. From the view of the spatial distribution about heavy metals, the high content of heavy metals are found in Industrial concentration areas, the heavy metals content of sediments from Urban area were higher than those in remote rural areas, Industrial areas were higher than high-tech agricultural zone.(3) The heavy metals mainly exist by residual speciation in the surface sediments from Yangling-Xingping section in Wei River. The direct harmful of heavy metals(Weak acid extraction speciation) are in the following order:Co(42.47%)> Mn (36.09%)>Pb (24.40%)>Ni(11.69%)>Zn(9.35%)>Cu(6.13%)>Cr(2.85%)>Fe(2.25%);The potentially harmful of heavy metals(reducible and oxidable speciation) are in the following order: Fe (39.37%) >Pb(38.60%)>Cu(28.66%)>Zn(22.49%)>Ni(21.73%)>Mn(17.66%)>Co(14.57%)>Cr(9.66%); Environmental and ecological risks of heavy metals(Weak acid, reducible and oxidable speciation) are in the following order: Pb(62.99%)> Co(57.04%)>Mn(53.75%)> Fe(41.62%)>Cu(34.79%)> Ni(33.41%)>Zn(31.84%)>Cr(12.51%).(4) Sediments are mainly concentrated in the range of<75μm._pH value and loss on ignition with decreasing particle size has a slightly increasing trend. Higher levels of the conductivity Concentrate in the bigger size. Higher magnetic susceptibility values appear in the small particle size of< 50μm and the large size of>900μm. The total content of heavy metals in sediments concentrate in the size range of< 75μm. High density of Cr focus on the small size, The larger values of Pb, Mn, Ni, Cu, As and Fe are distributed in the size range of<50μm,150-300μm and>900μm.The higher density of Co concentrate on the smaller and larger size range, but the lower density of Co concentrate on the medium size range.(5) Heavy metals chemical speciation are no significant difference in different size.The same speciation of Cu, Pb, Cr, Ni and Mn appear the same scale in the different size range. With the increasing size of sediments, the "Non-steady speciation "of Zn becomes decrease. Co mainly exists by "steady speciation"in the size of<75μm, but the "Non-steady speciation " mainly exists in the size range of 75-150μm and>150μm.(6) The correlation of heavy metals in the surface sediments show that Fe, Mn and other heavy metals have a good correlation, Pb, Cu, Zn and Ni have a higher correlation, the correlation of Cr, Co and other elements are not only week, but the trend shows a negative correlation. Pb, Cu, Zn, Ni, Mn, Fe, As show a significant correlation with CaO, K2O, MgO, Al2O3 and show a negative correlation with Na2O, SiO2 and pH value. Cluster analysis showed that Cu, Pb, Cr and Ni have a nearest clustering relations in the speciation of B1,B2 and B3. Mn and Zn are different with other heavy metals in the speciation of B4.(7) By comparing Environmental geochemistry with different city sections in the surface sediments of Wei River, the results show that there are the same spatial distribution rule with Cu, Pb, Ni and Mn, that means The lowest concentration appear in Yangling- Xingping section while the higher concentration appear in the city of Xi'an, Xianyang and Baoji. There are the same distribution rule with Cr and Zn, that means the maximum level appears in the Yangling-Xingping section and the other sections keep the same level. The Harmful of heavy metals in the different sections of Wei River are in the following order: Baoji> Xi'an> Xianyang>Yangling-Xingping._Overall, high levels of heavy metals always appear in the big cities where the industry is concentrated and the population are numerous. However, the unusual content of individual heavy metals in the remote areas should be high regarded. |
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