Study On Pollution Assessment And The Accumulation Law Of Heavy Metalsin The Sediments Of Harbin Section Of Songhua River

In this study, the sediments of Songhua River were selected as the main research object, we analyzed the heavy metals in the sediments on the spatial distribution, pollution characteristic, potential ecological risk based on total content and active component content, the adsorption law of heavy metals and nutrients under single-factor experiments and multi-factor orthogonal experiments. This study provides some theory reference for heavy metal pollution control and water ecological environment restoration in the Harbin section of Songhua River.From the heavy metal content of the sediments detection, Cadmium is seriously overweight compared to the heavy metal background values, zinc slightly overweight and others are much less than the background values. The result of comparison for hte concentration all the heavy metals is Zn> Cr> Pb> Cu> Cd. Among the four sampling sites, the one near Hejiagou outfall is the most seriously polluted, and the other sampling sits show an upward trend from the upstream to downstream. Multivariate analysis result that Cd and Pb has significant positive correlation and there are positive correlations between heavy metals Zn, Cu and Cr. Cd and Pb elements of the sediments are mainly from industrial waste water and municipal sewage pollution emissions. Zn, Cu and Cr elements are from natural rock, probably also affected by some human activities. Accumulation index evaluation results show that the pollution levels are from 2 to 3, and cadmium is the main pollution element. Potential ecological risk index evaluation results show that all of the four sampling are moderate intensive pollution, and the contribution of cadmium to the RI value is morn than 95%. In the analysis of exist status of heavy metals, the content of exchangeable Cd and Pb is higher, Cr and Cu mainly exist in organic matter-sulfide bounded form while Zn and Pb mainly exist in Fe-Mn oxides bounded form. Potential ecological risk assessment based on active component content showed that the values of RAC: Cd>Pb>Cr>Zn>Cu.The adsorption experiments of heavy metals under single factor results show that higher temperature is in favor of heavy metals’ adsorption to sediments in the early stage of the experiment, and the adsorption content would increase when temperature decrease later. The adsorption content of Zn, Cd and Pb are lower with lower p H, and the influence of p H on the three elements: Cd>Zn>Cr. The adsorption speed under turbulent flow is faster than that under laminar flow and stewing, the adsorption content of Zn and Cr: laminar flow>stewing>turbulent flow, while turbulent flow>laminar flow>stewing for Cd, the difference may come from two aspects: the influence of flow velocity to the concentration gradient mass transfer driving force and the influence of flow velocity to the thickness of effective adsorption layer. The results of enrichment experiment under different concentration of heavy metals show that the sediments still have large adsorption capacity for Cd and Zn, and the adsorption capacity for Cr is small. The enrichment experiment under multi-factor orthogonal condition show that the adsorption law under multi-factor orthogonal condition is similar to that under single factor condition, but the significance of difference of the results is reduced. The adsorption experiments of nitrogen and phosphorus under single factor results show that the adsorption content of TP and TN is higher under low temperature. The adsorption content of TN and TP under different flow velocity: laminar flow>stewing>turbulent flow. p H affect the enrichment of TN through affect physico-chemical adsorption process and ion exchange process, and affect the enrichment of TP by change junction state between phosphorus and metal elements and the ion exchange process of phosphate radical and hydrogen phosphate, overly both acidic and alkaline environment is not conducive to the enrichment of TN and TP.