Heavy Metal Pollution Characteristics And Impact Mechanism Research In Sediments Of Huiji River In Kaifeng

In this study, surface sediment and vertical sediment samples were collected from Huiji River of Kaifeng region as the research object, and the concentrations of heavy metals?Cd, Cr, Cu, Ni, Pb and Zn?, its physico-chemical properties in surface samples and the speciation of heavy metals in the vertical samples were measured by standard methods. Using geo-accumulation index and potential ecological risk index to assess the potential ecological risk levels of heavy metals in river sediment. The results indicated that:?1? The average concentrations of Cd, Cr, Cu, Ni, Pb and Zn in the whole river surface sediments were 24.51, 67.86, 290. 65, 28.46, 115. 34 and 1936.95 mg?kg^-1, respectively. The concentrations of Cd, Cu, Pb and Zn were significantly higher than those in fluvo-aquic soil of China, and the coefficient of variation of heavy metals in the surface was more than 49%, which may be the point source pollution. On the tributaries of the river, the concentrations of six heavy metals in the surface samples in the order from the high to low were: Huafei River > Huiji river > Majia River > Huangbian River, the contents of heavy metals in sediments are unevenly distributed along the river.?2? In six sections, the content of Cd, Cu, Pb, Zn in the lower section of each river?H2, H4 and H6? was larger than Cu, Pb and Cd that of the upper stream?H1, H3 and H5?. Zn and Cd were mainly extracted from the residue and weak acids, and Cu and Pb were mainly dominated by residue. The content and percentage composition of different heavy metals in different sections were different, and also there was no regularity of distribution.?3? The mean value of pH in the surface sediment of the whole sample was 7.51, which was neutral to slightly alkaline. The mean of each tributary sediment pH in the surface samples were in the order: Huangbian River > Majia River > Dong hucheng River > Huafei River > Yaochang River > Huiji River; the average concentrations of sediment organic matter content was 88.87g?kg^-1, which was significantly higher than that of Kaifeng city average soil organic matter content, the mean of each tributary sediment organic matter contentin in the surface samples were in the order: Huafei River > Huiji River > Yaochang River > Dong hucheng River > Huangbian River > Majia River; the average volume fraction of clay, silt and sand in the range of particle size were 11.41%, 72.50% and 16.01% respectively, and silt was the main component of sediment granularity size, the median diameter of each tributary sediments in the surface samples were in the order: Dong hucheng River?18.16?m? > Huangbian River?16.51?m? > Huiji River?15.89?m? > the Whole river?14.88?m? > Huafei River?13.50?m? > Majia River?12.53?m?. The change of both pH value and particle size composition of each tributary surface sediments were not very different, however, the variation of sediment organic matter content was larger among the various branches.?4? The pollution sources of Pb, Cr, Zn and Cd in the whole river sediment may be the same, and the pollution sources of Cr and Pb and Zn may be similar. The distribution of pollution sources was the main factors that influence the contents of heavy metal in sediment, there was no significant correlation among the heavy metals in surface sediments from the associated with pH. Cd, Cr, Pb, Zn and organic matter was positively correlated. With the increase of particle size, the heavy metal elements and grain size between the correlation gradually from the significant correlation to not significant correlation. There was a significant positive correlation between the heavy metal and 0⁴um grain size, and the correlation was not significant between >63um grain size.?5? For the accumulation index of heavy metals in surface sediments, in terms of Chinese fluvo-aquic soil element background value as the benchmark, the mean of Cd, Cr, Cu, Ni, Pb and Zn accumulation index(I_geo) was 4.49,-0.84, 1.28,-0.72, 0.86 and 1.63 respectively, namely Cd, Cr, Cu, Ni, Pb and Zn belonged to 5?strongly to very strongly polluted?, 0?practically unpolluted?, 2?moderately polluted?, 0?practically unpolluted?, 1?unpolluted to moderately polluted? and 2?moderately polluted? level. When reference value was choosed the highest background value of heavy metals in sediments before industrialization, the mean of Cd, Cr, Cu, Ni, Pb and Zn accumulation index?Igeo? was1.21,-1.27, 0.23,-1.92,-0.82 and 0.33 respectively, namely Cd, Cr, Cu, Ni, Pb and Zn belonged to 2?moderately polluted?, 0?practically unpolluted?, 1?unpolluted to moderately polluted?, 0?practically unpolluted?, 0?practically unpolluted?, 1?unpolluted to moderately polluted? level. That indicated: Cr and Ni were mainly clean as a whole, which did not constitute a pollution hazard, Cu, Zn and Pb what was major pollution factors had already had signs of accumulation of existing pollution, Cd had been seriously polluted, which was the main pollution factor in the research area sediments.?6? The evaluation of six kinds of heavy metals in the surface sediments with the method of potential ecological risk assessment showed: reference value were choosed the highest background value of heavy metals in sediments before industrialization and Chinese fluvo-aquic soil element background value respectively, the potential ecological risk of heavy metals in sediments was in the same order as: Cd > Cu > Zn > Pb > Ni > Cr, we knew the potential ecological risk of Cd is very high, which was the most important ecological risk factors in the study river. From the sampling point RI space can be known, the comprehensive potential ecological risk of seventy-five samples were all “very strong” level. Relative to the upper reaches of Huiji river samples, potential ecological hazard level of Huiji River downstream sampling points were higher, most of the Majia River samples RI were relatively low, while the Huafei River samples RI were the highest risk level in the tributaries of research rivers. Among them, the most serious pollution river reach were Huafei River and Huiji River downstream, which need to strengthen the long-term monitoring and management of the later engineering dredging.