Research And Application Of The Maximum Diffusion Flux Method For Typical Pollutants At The Sediment-Water Interface

The ecological hazards caused by eutrophication heavy metal pollution have become major environmental problems.The sediment-water interface is a necessary way for pollutants to exchange materials between sediment and overlying water.Generally,the diffusion flux of pollutants at the interface is used to characterize the migration rate and direction of pollutants,which can be used to predict the risk of pollutant release.Therefore,obtaining in-situ data on the diffusion flux of pollutants at the sediment-water interface is critical to controlling the release of pollutants.This study established a new method?MFSI method?which is different from the traditional method,it can be used to obtain the maximum diffusion flux of pollutants?including potential release?in situ.The effectiveness and applicability of the method are tested and optimized.It was put into use in the laboratory and Xuanwu Lake with a view to evaluating the release of pollutants.The main results obtained are listed below.?1?By comparing the results of this method with the concentration gradient method and the mass balance method,it can be proved that the results of this method are consistent with the traditional methods.The results of this method can be referred to as the maximum diffusion flux of pollutants over a period of time and are used to estimate the potential release risk of pollutants.By fitting the linear relationship between the concentration of dissolved pollutants in the overlying water and the maximum diffusion flux of the pollutants,it is concluded that the MFSI method is effective for elements such as PO₄^3-,NH₄⁺-N,NO₃^—-N,Zn,As,etc.The results of elements such as Cd,Ni and Mn are poor.?2?It can be seen by simulating different temperatures and redox conditions in the laboratory,the release of Cr and Zn are strong under low temperature and aerobic conditions.The release of PO₄^3-,As and V is strong under high temperature and anaerobic conditions.There is no significant difference in the release of Cu under different temperatures and redox conditions.?3?The devices of MFSI method were placed in Xuanwu lake to obtain the release risk of different elements in winter,it can be proved that all of other elements show a tendency to diffuse and release from sediments to overlying water except Zn,NH4⁺-N,Cu,V in the North Lake.In the southwestern lake area,all elements show a tendency to diffuse and release from sediments to overlying water except V.All elements show a tendency to diffuse and release from sediments to overlying water in southeast lake.The potential release risks of NH4⁺-N,NO₃^--N,PO₄^3-,As and Cr in the three lake areas are high.