Effects Of Microcystis Aeruginosa On Migration Of Heavy Metals In Sediments

Heavy metal with high toxicity and bioaccumulation effect raises people’s attention because it makes human health under risk.The migration of heavy metals in surface sediments involves a series of physicochemical processes,such as adsorption desorption,dissolution absorption,complexation dissociation,as well as biological oxidation and reduction.When nitrogen and phosprus in water environment are suplus,algae outbreak occurs and hence water environment turns to eutrophication.The active algal activity is closely related to the migration of heavy metal in sediment,so does the organics degradation and microbioactivity in eutrophication water.Therefore,it is of great significance to study the effects of Microcystis aeruginosa on the migration of heavy metals in sediments.In this paper,the sediment and overlying water in the receiving water body were taken as the research objects,and the effects of algae organic matter and algae cells on the migration of heavy metals in the sediment were compared by using the research methods of simulation experiment.The role of bacteria in the process of algae affecting the migration of heavy metals in the sediment was explored by simulating the bacterial and sterile environment,and the effect of bacteria on the migration of heavy metals in the water was analyzed.The migration behavior of heavy metals in sediments was further relvealed by distribution of metal particles and dissolved state.The main results are as follows.In the sterile and non-sterile environment,the p H value,dissolved oxygen（DO）concentration and redox potential（E_h）of overlying water were significantly varied when algal orgnic matter（AOM）and algae were added.Meanwhile,the concentrations of organic matter and nutrients（phosphate,ammonia nitrogen and nitrite nitrogen）in overlying water and interstitial water also fluctuated.In sterile environment,E_h in column with AOM and algae decreased 0.56 m V and 88.30 m V respectively,and Eh in the non-sterile column dececresed more dramatically,with the value of 200.40 m V and 277.00 m V respectively.Similarly,ammonia concentration in in column with AOM and algae in steric condition increased-3.89 mg·L^-1 and 1.47 mg·L^-1 respectively,and the values were even bigger as4.15 mg·L^-1and 11.44 mg·L^-1in non-sterile condition.The variation of these factors showed that AOM and algae activity turned the water environment to reductive condition which benefited the relase and migration of heavy metal in suspended particle and sediment.Comparing the migration of heavy metals in sterile-AOM column and sterile-algae column,it showed that both AOM and algae obviously promoted the release of Sb and As,but slightly promotes the release of Pb.The biggest observed concentration of Sb,As and Pb in overlaying water were 0.93μg·L^-1,0.00μg·L^-1 and 0.00μg·L^-1,respectively,in sterile-AOM column,and 4.51μg·L^-1,11.14μg·L^-1,0.93μg·L^-1 respectively,in sterile-algae column.During the migration of Sb,As and Pb from sediments to overlying water,it was found that algae activity benified the release of Sb from sediment to water in dissolved form in the steric condition,while As and Pb were first relased to water in particulate form and than transfer to dissolved form.When biggest release occurs in sterile-AOM column,the concentration of particulate Sb,As and Pb in water were 1.96μg·L^-1,4.04μg·L^-1 and 2.89μg·L^-1respectively,and the concentration of dissolved form were 0.80μg·L^-1,1.99μg·L^-1and1.62μg·L^-1 respectively.In sterile-algae column,the concentration of Sb,As and Pb in particulated form decreased by 0.65μg·L^-1,1.44μg·L^-1 and 0.05μg·L^-1 respectively,and increased by 4.14μg·L^-1,12.79μg·L^-1and 0.52μg·L^-1,respectively,in dissolved form.Microbioactivity promoted the release of Sb and As in dissolved form induced by AOM and algae activity.Particulate Sb,As and Pb in non-sterile-AOM column were 1.93μg·L^-1,2.55μg·L^-1 and 3.23μg·L^-1,respectively,while dissolved Sb,As and Pb were 4.51μg·L^-1,12.48μg·L^-1 and 5.51μg·L^-1.Turning AOM to algae,Particulate Sb,As and Pb in non-sterile condition increased by 0.74μg·L^-1,0.25μg·L^-1 and-1.78μg·L^-1,while dissolved concentration increased by 1.45μg·L^-1,3.41μg·L^-1 and-1.14μg·L^-1.