Assessing The Pollution Level And Spatial Characteristics Of Water And Sediments In The Haihe River Basin

The large and medium-sized reservoirs distributed in the western and northern parts of Haihe River Basin (HRB) play a key role of the drinking and agricultural water supply in the densely populated region. So the reservoirs’ water environment situation and its spatial characteristics required comprehensive evaluation and further research.25 typical reservoirs in HRB were selectd in this study, and their surface sediments and overlying water were sampled. The pollution levels of heavy metals including As, Cu, Zn, Cr, Ni, Pb, Cd were assessed by using the methods of geoaccumulation index and potential ecological risk index, the water quality was comprehensive evaluated through the method of Principal Component Analysis (PCA), and the eutrophication status of reservoirs was assessed by using the logarithmic power function. In order to study the spatial characteristics of reservoir water environment, upstream and downstream river samples were also analysed. The main conclusions were as follows:1) For the assessment of heavy metals of sediments. Seven kinds of heavy metals all exceeded the background values in 25 reservoirs sediments, Cd was the most common, as many as 22 reservoirs’ Cd was beyond its background value. The results of two evaluation methods were respectively Cd> Pb> Zn> Cu> Cr> Ni> As and Cd> As> Pb> Cu> Ni> Cr> Zn. The level of Cd pollution was the highest, The average of potential ecological risk coefficient (Ef1) of Cd in all reservoirs belonged to the moderate hazard rating, the Cd’s Ef1 of more than half of the reservoirs belonged to moderate hazard level and above. The Ef1 of As, Pb, Cu, Ni, Cr, and Zn all belonged to slight pollution levels.2) For the assessment of water quality. The content of nitrogen, phosphorus of reservoirs in HRB was generally beyond the standrads. The mean concentration of total nitrogen (TN) of 25 reservoirs was 2.26 times that of the surface water standard V class, and total phosphorus (TP) was 10 times that of surface water standard V class for lake and reservoir. The results of water quality comprehensive assessment showed that the water quality of large and important water source reservoirs was relatively better than the reservoirs with a smller capacity. However, the water quality of some water source reservoirs was not good. The water quality of reservoirs located in Luanhe River Basin was worse than the other areas of HRB. The degree of reservoir eutrophication in HRB was serious as a whole. There are 20 reservoirs belonged to "eutrophic". The reservoir capacity was relatively smaller, the eutrophication degree was higher. However, the eutrophication degree of some water source reservoirs was more serious.3) For the comparative analysis of reservoirs and rivers. The Ef1 of Cd and Cu of river sediments was higher than the reservoir sediments, the mean Ef1 of Cd belonged to "strong" pollution levels. The Ef1 of Pb, Ni of upstream river sediments was also higher than the reservoirs. There were no significant differences of Cr and Zn ecological risks among the upstream, downstream river sediments and reservoirs. From upstream rivers to reservoirs, and then to downstream rivers, the El curve respectively showed three types, namely "V", inverted "V" and "decreasing". "V" curve represented the water source reservoirs; inverted "V" curve represented the reservoirs located in Luanhe River Basin, the large-area cage aquaculture was the main reason for the formation of the reservoirs eutrophication; the reservoirs of "decreasing"curve were relatively diverse, the eutrophication of Yongding River Basin was more serious.