| Water pollution has always been an environmental problem worldwidely in the past decades.China is also a country with a lackage of fresh water resources.With the rapid economic development,the problem of water pollution has become increasingly prominent,resulting in a worsened situation of water resources in China.Because Qingshan Lake is one of the sources of Taihu Lake and Qiantang River,its water quality is closely related to the safety of the local drinking water.Therefore,it is of great significance to steadily improve the water environment quality of Qingshan Lake watershed.In this study,the Qingshan Lake small watershed in Hangzhou was selected as the research object.Based on the systematic investigation of Qingshan Lake watershed and the analysis of water samples in all periods of the watershed,the pollution characteristics of the water body was analysed and evaluated via the single factor water quality evaluation method and Nemerow comprehensive pollution score method;meanwhile the the pollution source risks of each town within the watershedwas assessed through the river entry coefficient method.The specific research results are as follows:1.Based on the analysis of the chemical characteristics of the water body in Qingshan lake basin,phosphorus was the main contributor causing water pollution in the basin.Aaccording to the National Ssurface Water Environmental Quality Standard(GB3838-2002),the parameter concentration of more than 74%of 936 samples collected exceeded the Class ? Standard Limit(13 monitoring sections including reservoir outlet and tributary sections);and that of 32%of samples exceeded the Class ?Standard Limit and therefore the water quality was classified as Class ? water.The parameters of the outlet section and tributaries entering the reservioir of Qingshanhu Reservoir exceeded the standard by 89%and 73%,respectively.According to Nemerow's comprehensive pollution index analysis,it is found that 69%of the data above the serious pollution level in each tributary of the reservoir account for the total,which is in good agreement with the over-standard rate of the parameters.Therefore,the pollution in Qingshan Reservoir Basin is mainly attributed to a single factor.Combined with the single factor index analysis,it was concluded that TP in Qingshan Reservoir Basin is the major contributor for deterioration of water quality.2.The hydrochemical characteristics in Qingshan Lake Basin showed significant temporal and spatial distribution changes:from the time distribution,TP concentration in the watershed shows a higher concentration in wet season compared with that in normal and dry seasons;From the perspective of spatial distribution,TP mainly flowed into Qingshan Lake Reservoir from Ban Qiao and Taihuyuan Town through three streams namely Lingxi,Panxi and Nantiaoxi respectively,which is the main source of TP leading to exceedance of water quality over the national standard in Qingshan Lake Reservoir.3.The main pollution sources and relevant contribution rates at each town within Qingshan Lake watershed were analyzed by using the river inflow coefficient method.There were mainly three pollution sources in the whole watershed in terms of agricultural pollution sources,domestic pollution sources and industrial pollution sources,of which agricultural pollution sources was the biggest contributor toward the concentration contribution rate of various pollution parameters,followed by domestic pollution sources and industrial pollution sources,respectively.The TP from agricultural pollution source TP has reached 90%of contribution rate,which implies that TP is the main pollutant attributed to the degradation of water qualtiy. |
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