| With the rapid progress of society and economy,human activities have caused the destruction of aquatic ecological environment and human health problems,among which the pollution of heavy metals in river sediments has become increasingly serious.So research on heavy metal pollution in river sediments has become particularly important.This paper mainly describes the characteristics of heavy metals in river sediments and pollution risk assessment.The characteristics analysis mainly includes three parts: content level,distribution characteristics and pollution source analysis.Combined with heavy metal content levels and distribution characteristics,principal component analysis and correlation analysis and R-type cluster analysis were used to analyze pollution sources.In the pollution risk assessment,by constructing a pollution assessment method based on combined weighting and gray cloud model,the evaluation results of heavy metal pollution of river sediments are obtained.More importantly,the combination of weights is used to determine the heavy metals by analytic hierarchy process and entropy weight method.The subjective and objective weights of the indicators are combined,and then brought into the normal gray cloud whitening weight function model,and the pollution level determined by the integrated gray cloud clustering coefficient is obtained.Finally,the fuzzy entropy is introduced as the second auxiliary quantity,and the river pollution evaluation grades together constitute a two-dimensional evaluation system.This paper comprehensively analyzes and evaluates the heavy metal pollution of sediments in the rivers of the Biliuhe Reservoir Protection Planning Area.The main analysis and evaluation results are as follows,characteristic analysis shows that the average values of eight heavy metals such as Cr,Cu,Ni,Pb,Zn,As,Cd and Hg are generally low,the content of heavy metals in some points is relatively high,but there is no obvious regularity in the water period sequence;Source analysis shows that the sources of heavy metal pollution may mainly come from the enterprise emissions in the upper reaches of the river and the unreasonable application of chemical fertilizers and pesticides.The traditional weighting method is replaced by combination weighting,which shows that heavy metals such as Pb and As account for a relatively large proportion in each basin,and the pollution is the most serious;Pb is the largest in flood season and peaceful season,Among them,the heavy metal Pb weights in the wet season and the flat water period are 0.19 and 0.16 respectively,and the As weight in the dry season is 0.20,which has a certain degree of pollution risk.The results of grading evaluation based on combined weighting and grey cloud model show that the pollution degree is Bajiazi River,Wolong River,Geli River and Biliu River.And the gray types of each river are all classes I and II,and the overall pollution level is relatively light.Among them,the type I sediment grey cloud coefficient of Bajiazi River is the highest,followed by Geli River,which belongs to the category I standard.The contribution rate of type II sediment of Wolong River and Biliuhe River is 52% and 72% in the plain water period,and the type III grey cloud coefficient is small,so the overall pollution situation of the rivers is good.And the fuzzy entropy of each river is between 0.5 and 1.0.It is considered that the complexity of river sediment evaluation is relatively high,and the river has high complexity.Combining with the traditional method,it can be seen that the evaluation result based on grey cloud model improves the pollution level of the traditional method.The result has higher sensitivity,better discrimination and more realistic results.According to the evaluation results of regional rivers,this paper also provides effective monitoring and management measures and suggestions for the relevant departments from three aspects: identification of key areas,source control and feedback regulation management.Through the grey cloud model,the uncertainty transformation between quantitative and qualitative concepts can be achieved,which provides a new idea for qualitative evaluation of heavy metal pollution.It can also be used for reference in other ecosystem risk assessment. |
PDF Full Text Request