| Rainwater is a valuable resource that can be recycled.However,with the acceleration of urbanization,the increase of hard underlying surface and human activities lead to the aggravation of air and surface pollution,resulting in serious pollution of rainfall runoff.The key to the effective control of rainfall runoff is to analyze the pollution sources and identify the influencing factors.Taking the main urban area of Xi’an as the research object,based on the literature and measured rainfall runoff data,this study explored the pollution characteristics of non landing rainwater and runoff of different underlying surfaces in different functional areas.Nemerow index method was used for comprehensive evaluation of water pollution,and principal component analysis/multiple linear regression model(PCA-MLR)was used to further analyze the causes of pollution differences,logarithmic mean divisia index(LMDI)method was used to explore the influencing factors of the interannual dynamic change of water quality.The conclusions are as follows:(1)The results show that the nitrogen pollution of non landing rainwater in Xi’an city is serious,and the runoff from roof and pavement is mainly polluted by suspended solids and organic matter.The phosphorus content of runoff from green space is generally higher than that from roof and pavement;Three dimensional fluorescence spectrum parallel factor analysis results show that dissolved organic matter(DOM)of pavement runoff was more complex than that of roof runoff.DOM of roof runoff resolved three kinds of humus(C1,C2,C4)and one kind of fulvic acid(C3).DOM of pavement runoff resolved four kinds of humus(C1,C2,C4,C5),one kind of fulvic acid(C3)and one kind of protein(C6),With the increase of rainfall duration,the content of DOM decreased;The runoff of different underlying surface in each functional area mainly contains -OH,-COOH,benzene ring and other functional groups,C=C,C=O and other unsaturated bonds;Nemerow index comprehensive evaluation results show that the pollution degree of rainwater runoff in each functional area is:traffic area>industrial area>commercial area>cultural and educational area.The road runoff in traffic area and roof and road runoff in industrial area are heavily polluted,while the roof,road runoff and green space runoff in commercial area are heavily polluted,moderately polluted and polluted,respectively,the others are relatively clean,and the rainwater not falling to the ground is relatively clean.(2)Based on PCA-MLR model and using conventional water quality indicators(COD,SS,NH3-N,TP),DOC and DOM components,roof runoff was analyzed into two types of pollution sources.The first type came from atmospheric deposition,accounting for 44.2%of the runoff pollution,and the second type came from roof material precipitation and traffic activities,accounting for 55.8%;The contribution rate of traffic activities to runoff pollution is 39.8%,that of atmospheric deposition and soil erosion pollution is 22.4%,and that of domestic pollution is 37.8%.(3)Mann-Kendall trend test showed that COD concentration of non landing rainwater,roof runoff and pavement runoff all showed an upward trend,while TP concentration showed a downward trend.In the case of non landing NH3-N decreasing,NH3-N of roof and pavement runoff showed an upward trend,SS concentration of non landing rainwater and roof runoff showed a downward trend,but pavement runoff showed a slight upward trend.The decomposition results of LMDI model show that the contribution of technology improvement,industrial structure,economic development and population size to the quality of unflooded rainwater,roof runoff and pavement runoff is basically the same.Among them,technology improvement is the leading factor affecting water quality,followed by industrial structure,and economic development and population structure have a negative contribution to the improvement of water quality.In 2017,the effect of population structure increased sharply,which needs to be vigilant. |
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