Distribution And Pollution Assessment Of Heavy Metals In Surface Sediments From Dianchi Lake

Under the effective control of exogenous pollution sources in Dianchi Lake,endogenous pollution sources are increasingly becoming the main risk of pollution in Dianchi Lake.When the environment of the lake body changes,various metal ions in the sediments at the bottom of the lake will be released into the water body,causing secondary pollution.Therefore,the comprehensive analysis and evaluation of the pollution of heavy metals in the sediments of Dianchi Lake is significance for preventing the secondary pollution and fighting against the fundamental pollution of Dianchi Lake.At present,there is no authoritative and unified standard for sediment environmental quality in China.In the process of evaluating sediment pollution,the relevant provisions of the soil environmental quality standard(GB15618-1995)are often adopted,because there is a great difference between the formation process,the existence of the environment and the way of pollution in the sediment and soil.Using soil quality standards to evaluate sediments,the evaluation results are often inconsistent with the actual situation.In addition,there are many kinds of evaluation methods for heavy metal pollution in sediment,The commonly used the index of geoaccumulation,the potential ecological risk index and Nemero index have different targets,and there are corresponding deficiencies.In view of this,the environmental quality standard of sediment was established according to the Control standards for pollutants from agricultural use issued by the Ministry of agriculture.Using the analytical hierarchy process(AHP)model,combined with the calculation method of air pollution index(ATP),a new method for evaluating the pollution of heavy metals in sediments was proposed,considering the fuzziness,graduality and biological toxicity of metal elements.This method is used to evaluate the pollution of heavy metals in the surface sediments of Dianchi Lake from2010 to 2017.The results are compared with the index of geoaccumulation,The potential ecological risk index and the Nemero index,and the pollution status and change trend of heavy metals in the surface sediments of Dianchi Lake arecomprehensive analysed and evaluated.The results are as follows:(1)From 2010 to 2017,the contents of Pb?Cu?Cr?Zn?Hg?Cd?As in the surface sediments of Caohai section exceeded the maximum contents of heavy metals in the normal grain sediments before modern industrialization,and showed obvious geographical differences: the contents of seven metal elements in the sediments near one side of the Entrance of river into Caohai section were significantly higher than those on the other side,and the overall pollution level was grade v,which was serious pollution.The potential ecological risk index reached 1441,indicating that heavy metals in the surface sediments of Caohai section have a strong risk of ecological harm;For the surface sediments of Waihai section,Nemerow index is used to evaluate and the pollution level was grade ?,which was light pollution.According to the new evaluation method,the pollution grade is grade ? and the quality is described as basic cleanliness.As a whole,the pollution degree of heavy metals in caohai section sediment is much higher than Waihai section,which is the largest endogenous pollution source in Dianchi lake.(2)The pollution status of each metal element was evaluated by the index of geoaccumulation: the heavy metal pollution of caohai section sediment was more serious than Waihai section.except Cr,the pollution degree of Pb?Cu?Zn?Hg?Cd?As was between moderate pollution and strong pollution,and the pollution order was Cd > As > Cu > Hg > Zn > Pb > Cr.The pollution degree of the sediments in Waihai section is relatively light,which is only polluted by Cu and As,and the pollution degree ranges from no pollution to moderate pollution.(3)From 2010 to 2017,the potential ecological risk index,Nemerow index and Composite pollution index of caohai surface sediment showed the same trend.For the sediments of Waihai section,the variation trend of Nemerow index and Composite pollution index is completely consistent,but somewhat different from the variation trend of the potential ecological risk index,which is caused by the different emphases of the three evaluation methods.The results showed that the higher the concentration of pollutants,the more consistent the changes of the three indexes were.The above results reflect the distribution and pollution situation of heavy metals in surface sediments of Dianchi lake,and provide scientific basis for the treatment and protection of Dianchi lake.In the process of research,the assessment methods of lake sediment pollution were explored preliminarily,which made the assessment results of sediment pollution more scientific,comprehensive and reasonable.