| With the development of human society and the level of world industry and agriculture,the process of urbanization continues to accelerate, the resulting water pollution problems are becoming more and more serious. Among the many pollutants, heavy metals are one of the most serious pollutants in river water quality because of their persistence in the environment,the biogeochemical cycle and the potential ecological threats. While river sediment is the main carrier of heavy metals, affects the migration of heavy metals in water in the transformation process, on the one hand, the sediment particles can adsorb many kinds of heavy metal elements in certain dynamic conditions and deposition in the river bottom or floodplain, in a certain period of time to reduce the total amount of heavy metals deposit in the water, on the other hand, when the chemical dynamic external conditions change, the adsorption of heavy metals in sediment particles may change the occurrence, transfer from the adsorbed solid to dissolved water or sediment heavy metals in the sediments with scouring water can significantly change back into the overlying water chemical composition, two times or even cause water pollution. Therefore, it is significant to study the pollution of heavy metals in sediments.In this paper, the basic physical and chemical properties of sediments in the middle and lower reaches of Weihe River and its tributaries were studied by field investigation, sample collection and detection analysis in the middle and lower reaches of Weihe River and its tributaries. At the same time, after the flood in 2014, In 2015, before the flood, flood,after the flood, Pb, Zn, Cr, Cu, Co, Ni content were determined. To explore the Weihe River downstream of heavy metals in sediments of longitudinal distribution characteristics, vertical distribution characteristics and temporal characteristics, Also through the correlation analysis discussed the relationship between the heavy metals and heavy metal elements and sediment physicochemical properties, the final analysis of the main sources of heavy metals and also based on heavy metal accumulation index and potential ecological risk index to evaluate the pollution status of heavy metals in sediments of Weihe River pollution, in order for the rational development and utilization of the Weihe River water resources, formulate measures for prevention and control of pollution and the watershed management planning to provide ascientific basis.The main conclusions of this study are as follows:1.the physical and chemical indicators of the surface sediments in the middle and lower reaches of Weihe were: The average value of p H was 7.37, the average conductivity value was364 s/cm, the low frequency magnetic susceptibility and high frequency magnetic susceptibility were 73.04 and 70.61m3/kg;The physical and chemical indexes of the surface sediments from the middle and lower reaches of Weihe are: Average p H 7.45, the conductivity value of mean value 347.34 s / cm, the low frequency magnetic susceptibility and high-frequency magnetized rate respectively 64.27, 62.75m3/kg, grain size analysis results show, the results of grain size analysis show that the sediments in the middle and lower reaches of Weihe are mainly dominated by silt and sand.2.From the content of six kinds of heavy metal elements in Weihe, The average of the six elements is compared with the soil background values of Shaanxi Province, and the average of the six elements is different than the background value. The mean values of the six elements are different than the background values.3.From the point of view of the distribution of heavy metal elements in Weihe, Six kinds of elements in the enrichment of Guo town bridge of Baoji Wolong bridge, the highest temple,followed by Xianyang. They are all the more close to the city. the Gengzhenbridge,Shawangdu, Shuyuan are at the lowest level of enrichment degree. The enrichment of Qingjiang River and Bahe River elements is very high, the content of heavy metals in the Jing River and Laoriver is very low. This shows Weihe Baoji section and Xianyang section of the Qingjiang River and Bahe, by the more serious pollution.4. The content of heavy metals in the sediments from the middle and lower reaches of Weihe in different periods, The contents of heavy metals in flood after the highest, followed by the flood, before the flood season was the lowest. The content of heavy metals in contrast to the Weihe after the flood in 2014 and 2015 after the flood, It can be found that the content of heavy metal elements Pb, Zn, Cr, Cu and Ni in 2015 is higher than that in 2014. This shows that in 2014-2015 years of the year, the heavy metal enrichment in Weihe increased, Weihe is still being sustained pollution.5. The geo-accumulation index and potential ecological risk assessment of heavy metals in sediments from the middle and lower reaches of Weihe River and its tributaries, the geo-accumulation index of all sampling sections in Weihe was less than 0, single potential pollution index and potential ecological risk index also has a low level, the potential ecological risk of Co, Zn, Cu, Pb, Ni, Cr in the middle and lower reaches of Weihe is lower. |
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