Study On The Characteristics Of Redox And Transformation Of Heavy Metals And Nitrogen In The Surface Sediments Of BaiyangdianLake

Generally speaking,After the external source input of the water in the basin is effectively controlled,the internal source may become the main source of pollution input,threatening the environmental quality of the water.As a typical inland shallow lake in northern China,Baiyangdian Lake?BYDL?is facing important environmental problems currently such as sediment nitrogen pollution and heavy metal pollution due to the discharge of untreated domestic and industrial wastewater before.With the continuous in-depth understanding of the water pollution process and its internal mechanism,the treatment of contaminated water has been greatly improved.Nowadays,it is mostly treated by ecological restoration methods,of which the restoration of aquatic vegetation is the main measure.This article takes surface sediments of BYDL as the research object,and studies the redox characteristics and influencing factors of BYDL surface sediment by measuring the content of Eh and its influencing factors OM and AVS of surface sediment in BYDL.Then analyze the heavy metal morphology of sediments at 40 sampling points in BYDL,through the laboratory simulation of the oxidative state of the rhizosphere of the aquatic plant during the vigorous growth period as well as the anoxic state of the rhizosphere after the aquatic plant stopped growing,to study the heavy metals pollution status and risk degree in the surface sediments of BYDL,and the effects of different redox conditions on the occurrence forms of heavy metals Cd,Cr,Cu,Ni,Pb and Zn in the sediments.In order to reveal the environmental effects of aquatic vegetation on heavy metals in surface sediments,and to provide a scientific basis for the ecological restoration and management of BYDL.This article also studies the nitrogen content and spatial distribution characteristics of which during the dry season and wet season,providing a basis for further water quality control and improvement in BYDL.The main research results are as follows:?1?The sediments of BYDL are weakly reducing sediments.In the surface sediments of BYDL,AVS and Eh showed a significant correlation,and OM and Eh showed a negative correlation.The content of AVS and OM in BYDL sediment will directly affect the level of Eh.The spatial distribution of OM and AVS content in the sediment of BYDL is quite different,and the distribution trend of the two is similar,which may be mainly related to the pollution degree in different areas of the lake.The OM content in the sediment during dry season was higher than that during the wet season,but the AVS content in the sediment during the wet season was slightly higher than that during the dry season.?2?The secondary phase content of Cd and Pb in the surface sediments of BYDL exceeds 50%of the total,and there is a high possibility of secondary release.The difference of heavy metal content in BYDL area is more caused by the change of secondary phase content.Analysis of pollution sources based on the risk of heavy metal forms shows that heavy metals Cd,Cu,Pb and Ni are more affected by human factors,while Cr and Zn are more affected by natural factors.?3?By simulating different redox conditions,the effect of aquatic plant remediation methods on the occurrence of heavy metals in the surface sediments of BYDL was studied.The results show that for the N4 point sediment with the highest heavy metal pollution in BYDL,anaerobic reduction conditions can increase the F3state ratio of heavy metals Cu and Ni,effectively reduce the proportion of F1 state of heavy metal Cd,and promote the transition from F2 state of Fb to F3 state.The aerobic environment can increase the ratio of Cd in F1 and available states,and reduce the ratio of Ni in available states.The risk assessment results show that anaerobic and extremely anaerobic environments could help to reduce the ecological risks of heavy metals Cd and Cu.For the D1 point sediment with the lowest heavy metal content in BYDL,the heavy metal content at this point is very low,and does not reach the local soil standard value.The influence of redox conditions is not exactly the same as that of point N4,and the overall change is small.The risk assessment results show that the risk of Cd is high at this point while the total amount of it is low that cannot pose a threat,and continuous oxygenation may increase the ecological risk of heavy metal Ni.?4?The concentration of NH₄⁺-N and TN in surface sediment samples of BYDL is higher than that of other lakes in China,indicating that endogenous nitrogen pollution in BYDL is more harmful to water quality than other lakes,and the release of endogenous nitrogen may become an important factor leading to the risk of eutrophication in BYDL.