Release Of Heavy Metals From The Water-sediment Interface Of Chaohu Lake Under Resuspension Disturbance

Heavy metal pollution has long been the focus of research by scholars at home and abroad.Lake sediments,as the enrichment center of various pollutants settling in water environment,are play an important role in material exchange and biogeochemical cycle in the lake.Sediment is not only the "gather" of heavy metals,but it is also an important internal pollution source of water.Resuspended sediments disturbed by external disturbances may cause some unstable heavy metals to be released again and re-enter the overlying water.In recent years,exogenous pollution input into the water environment of the Chaohu Lake has been effectively controlled,but the heavy metals are still important pollutants for the deterioration of the water environment in the lake area.This study took the surface sediments of the three sampling points at the entrance of the Nanfei River,the center of the West Lake and the center of the East Lake in the Chaohu Lake as the research object,investigated the water quality and the physical and chemical characteristics of the sediments in the typical waters of Chaohu Lake.Analyzed the distribution characteristics and hydrodynamic characteristics of heavy metals(Zn,Ni,Hg,As,Pb,Cu,Cr)in the water environment and sediments.The Y-type resuspension device was used to explore the content of heavy metal in the overlying water under the conditions of different disturbance intensity and duration.Based on the characteristics of the content changes during the disturbance,it is more in-depth to understand the increase in the concentration of heavy metals due to sediment resuspension.In order to prevent and control the internal secondary pollution in the lake more effectively and scientifically.(1)The contents of ammonia nitrogen,COD,TN and organic matter at the three typical sampling points in the lake area are all high.Affected by the outbreak of cyanobacteria in summer and the increase of water temperature,the eutrophication situation of the lake area is still severe.The heavy metal pollution in the western half lake was more serious,especially the mercury element pollution,which was higher than the heavy metal content in the center of the East Lake.The content of heavy metals in the sediments exceeded the background value,Cr and Ni were mainly in the residue state,while Zn and Pb accounted for a high proportion of available states.Zn was mainly in the extraction state and oxidation state of weak acid,while Pb mainly existed in the oxidation state and reduction state.(2)In the process of resuspension,the content of suspended particulate matter,p H,and DO were all related to the intensity and duration of physical disturbance.The content of heavy metals in the overlying water at the entrance to the lake increased gradually with the disturbance time and frequency,and the concentration increased with the depth of the water in the vertical distribution.The content of Zn,Ni,Hg,As,Pb and Cr in the overlying water of West Lake rose rapidly to the peak at the initial stage of disturbance experiment,then the subsequent content gradually decreased and stabilized,and distributed uniformly in the vertical direction.The soluble heavy metals in the center of East Lake was increase significantly in the middle of the disturbance process,but did not continue to increase,and the change trend of the heavy metals distributed on the particle phase was quite different.(3)By analyzing the release flux and distribution coefficient of heavy metals during resuspension,it was found that the release amount and release rate of dissolved heavy metals will slow down gradually with the passage of time,but small range of short-term disturbance can still cause a large increase in the concentration of Zn,Pb,Hg,Ni and other elements.Because of the difference properties of sediments and the form of heavy metals in the lake,the particles suspended in the water have different release degrees and speeds of the heavy metals.However,it is still inferred that the sediment resuspension can bring more heavy metal pollutants to the upper water,especially the water-sediment interface.