Characteristics And Ecological Risk Evaluation Of Heavy Metal Pollution In The Upper And Middle Reaches Of Heihe River

Rivers are an important channel of global material circulation,and healthy material transportation and river ecosystem are the basis for ensuring the persistent progress of social economy in the basin.In last several years,in a row of China’s industrialization and urbanization,the trouble of heavy metal increase is becoming more and more sticking out.Heihe River,as the second largest inland river in China,attracted much attention because of the illegal exploitation of mineral resources in Qilian Mountain area,which causes water quality pollution and ecological environment damage.In this paper,the soil along the river and the studied of the Heihe River,this paper orderly investigated the spatial change characteristics of heavy metals in the river,compared and discussed the contact about heavy metals in water and sediment,in order to identify the dominant factors affecting heavy metal pollution in different regions,to explore the index of geoaccumulation and potential natural risk of heavy metal pollution in the Heihe River,and show a theory for the northwest inland river basin It provides theoretical basis for the effective and scientific management.The main conclusions are as follows:（1）According to the analysis of sediment physical and chemical indexes in Heihe River,the content of nitrogen and phosphorus nutrients in river sediments is low,and the spatial distribution is different,the order of physical and chemical indexes in different areas is main stream reach>whole reach>tributary reach,and the maximum and minimum values appear in the main stream.From the measure of heavy metals in the sediment of the upper and middle reaches of Heihe River,it can be concluded that eight kinds of heavy metals are basically higher than the background value of the sediment,and the order of different regions is tributary river>whole river>reservoir sediment,in which the pollution of heavy metals Cd,Pb and Zn is the most serious,mainly from human pollution,and there are serious point source pollution in individual points,and the non reservoir sediment is affected by human activities Bigger.The coefficient of variation of the eight heavy metals showed strong variability and obvious spatial difference,which may be related to the long-term intensive industrial and mining activities in some areas and the damming and interception of relevant river sections.（2）On the basis of physical and chemical indexes of Heihe River,the water quality of Heihe River is fine,mainly in categories II and III,in which the main pollutants are TP and TN.The spatial distribution is uneven,which is manifested as:main stream reach>whole reach>tributary reach.Heavy metal analysis show that heavy metals in the Heihe River is low,which contents the class I water quality standard,and the main matter is Mn that is 0.3127 mg·L-1.The main heavy metals in Heihe River is different,which is manifested as:the main stream reach>the whole reach>the tributary reach.The main reason for the spatial distribution difference of heavy metals in the upper and middle reaches is that the point source pollution caused by the industrial park near the main stream reach and the dam interception changed the cumulative trend.（3）In the upper and middle reaches of Heihe River,the relevance analysis shows that As,Cd,Cu,Zn and Pb as well as Cr and Ni have the same or alike pollution sources,and Mn is in a relatively natural distribution;the heavy metals in water Ni,Cu,Zn and Cd have similar or similar release sources,and the heavy metals Cr⁶⁺and Mn,Pb interact in the same remove and conversion.Principal Component Analysis showed that the major pollution justification of heavy metals in the Heihe River was industry,mining,agricultural and other human activities,and the principal components of water and sediment were basically the same.（4）Ecological risk assessment of Heihe River show that is basically non-polluting,and there is strong pollution in the main stream agricultural irrigation area.Heavy metal Cd、Cu、Pb are strong ecological risk;the main pollutants in water are Mn、Zn、Ni.