Study On Environmental Geochemisstry Of Heavy Metals In Daihai And Dalinuoer Lake

Natural water is a complex multiphase electrolyte system that contains a variety of inorganic and organic matter. AS heavy metals are components of this system, its chemical behavior is necessarily affected by the whole system. Heavy metals pollution in lake sediment is one of the environmental problems facing the world. As one of the widely existing in the nature, heavy metals can be the indicator of water pollution, reflect condition of water-sediment system, while threaten the complex ecosystem of "nature-economy-society" directly or indirectly. So it has important practical significance to recognize the impact of heavy metals on the ecological environment using environmental risk assessment of heavy metals in lake sediment.The objects of this study are sediments of Daihai Lake and Dalinuoer Lake in northern China. Based on the speciation analysis of heavy metals in both lake sediments, the speciation of heavy metals and the contents and distribution characteristics of AVS and SEM in lake sediment which have different geological background and different types of water quality are compared systematically; the transition and transform rule of heavy metals are discussed in both lake sediments; the relationship between distribution characteristics of speciation and the biological effectiveness of heavy metals in both lake sediments are revealed; being used assessment methods such as the method that is based on the total amount and speciation of heavy metals and∑SEM/AVS ratio, potential hazards of heavy metal pollution in both lake sediments are predicted and sentenced. The major conclusions are as following:1. The water quality type of Daihai Lake and Dalinuoer Lake is different. The former is I type water of sodium chloride class group, and the latter is I type water of sodium carbonate group. The dissolve solids of both lake have gradually increased since the beginning of the late1990s. Up until2011, the Cl" and Na+of both lake have increased significantly, and the imbalance of Ca/Mg ratio of Daihai Lake especially should be paid close attention.2. Speciation analysis shows that the dominant speciation of Pb (43.56%of the total) and Cd (65.25%of the total) in the sediments of Daihai Lake is iron and manganese oxides, while the dominant speciation of Pb (36.62%of the total) and Cd (43.89%of the total) in the sediments of Dalinuoer Lake is carbonates. Overall, the bio-available speciation of heavy metals (including Cu,Pb,Zn,Cd) in Dalinuoer Lake sediments is higher than those in Daihai Lake, which reveal that potential ecological risk of those four kinds of heavy metals in Dalinuoer Lake sediments is higher. The dominant speciations of those four kinds of heavy metals in the lakes not only show the difference of the geochemical features among four kinds of heavy metals, but also reveal the difference of lake water quality types and evolution stages between two lakes.3. Study shows that the average SEM/AVS ratio in both lake sediments are greater than1. So they would have toxic effects on benthos. Although the SO42-concentration (170.30mg/L) of Daihai Lake is far less than Dalinuoer Lake (328.28mg/L), the high salinity (6759.20mg/L), high basicity (3201.20mg/L) and high pH (9.5) of Dalinuoer Lake inhibit the activity of sulfate reducing bacteria so as to make SO4-2be preserved, which leads to the AVS concentration of Dalinuoer Lake is far less than Daihai Lake. This result reveals that the AVS content of Dalinuoer Lake sediments have weak control effects to the heavy metals. In addition, a lot of SO42-in the cooling water discharged by a coal-fired power plant built on Daihai Lake south shore and lower Eh (the average Eh is-139.27mV) of Daihai Lake result in forming a lot of AVS.4. The results of speciation analysis, SEM/AVS ratio and a variety of comprehensive assessment show that Cd and Pb in both lake sediments have the highest potential ecological risks and they are priority control pollutants in heavy metal pollution of watery environment.5. Using three different evaluation method, the evaluation result of heavy metal pollution in the sediments of tow lakes is not consistent. The evaluation results based on the evaluation method of the total amount of heavy metals (except the method of sediment quality criteria) are basically identical, and the sediment pollution level of Daihai Lake is higher than Dalinuoer Lake. Using evaluation method based on forms, the sediment pollution level of Dalinuoer Lake is higher than the Daihai Lake; Using the evaluation method of. SEM/AVS, the results are similar(SEM/AVS in Dalinuoer and Daihai Lake is1.46and1.55respectively). This may be related to the characteristics of evaluation method, the application scope and their limitations. So it is necessary to use a variety of evaluation methods comprehensively in order to complement each other.