Speciation And Distribution Of Heavy Metals And Diffusion Fluxes Of P And Fe At Micro-Interface In Chaiwopu Lake Sediments

Water sediment is an important repository of heavy metals.When the water environment changes(such as lower pH or higher redox potential,etc.),sediments become a potential source of heavy metals pollution.Chaiwopu Lake,as a national wetland park,is characterized by strong Xinjiang customs and rich tourism resources.In recent years,Chaiwopu Lake is facing the risk of water quality decline,water quantity reduction and degradation of aquatic ecosystems due to human activities.It poses a serious threat to people's life and health,agriculture and industry.Twenty-four sediment samples and seven DGT samples were collected from Chaiwopu Lake in southeastern Urumqi,Xinjiang.The contents of Zn,Cu,Cr,Ni and Pb in sediments were determined by atomic absorption spectrophotometer.The occurrence forms of heavy metals in sediments were analyzed by BCR three-step continuous extraction method.The pollution of heavy metals in lake sediments was evaluated by ground accumulation index method and potential ecological risk index method.The in-situ high-resolution distribution information of P and Fe at sediment-water micro-interface can be obtained by using diffusion gradient technique.Based on the accurate spatial distribution information of P and Fe at water-sediment interface,the synchronous change of P and Fe at sediment-water micro-interface and the release flux can be studied,which will be helpful to further explore the mechanism of phosphorus pollution in water.It can provide reference for Urumqi to realize water resources protection,reasonable exploitation and utilization of Chaiwopu Lake resources,environmental monitoring and water environment protection.Through the research,the following conclusions are drawn:(1)The content of heavy metals in all sampling sites of Chaiwopu Lake sediments did not exceed the national environmental quality standards,only the average content of Cr did not exceed the background value of Xinjiang soil.The results of spatial distribution analysis of heavy metal content in sediments show that the total heavy metal content of S6 and S7 is high,while that of s9,S8 and s 22 is low.The occurrence forms of Zn,Cu,Cr,Ni and Pb all take the largest proportion of residue forms.The results of correlation analysis show that Cu,Zn,Ni and PB are of the same origin,while Cr is of different origin.(2)The evaluation results of the geoaccumulative index show that the sediments of Chaiwopu Lake have been moderately polluted by Zn,Pb and slightly polluted by Cr and Ni.The results of the potential ecological risk index level show that the ecological risk grade of heavy metal pollution in Chaiwopu Lake sediment was A,and the ecological hazard degree was relatively weak.The order of hazard degree of each element was Pb > Ni > Cu > Cr > Zn.The contribution rate of Pb to the comprehensive potential ecological risk is 40 %.Lead pollution must be paid attention to.(3)The spatial distribution trends of available P and Fe in sediments from different sampling sites are basically similar.There is a significant correlation between available P and available Fe,which confirms that the release of available P and available Fe in Chaiwopu Lake sediments is synchronous.The diffusion fluxes of phosphorus and iron at the sediment-water interface are mostly negative,showing that P and Fe diffuse from overlying water to sediment.The sediments of W3 ~ W6 sample points have been used as sinks of available phosphorus in overlying water,which has played a role in buffer phosphorus pollution to a certain extent.There was no significant correlation between P release flux and pH,ORP,conductivity,TDS of overlying water and pH,salinity(Ca,Mg),nutrient(organic matter)of sediments.The release flux of Fe is affected by the sediment pH.