| In recent years,pilot construction of sponge cities has been actively carried out across the country.As the overall construction of my country’s sponge city is still in the exploration stage,lack of theoretical support and technical guidance,the actual effectiveness of some sponge facilities is lower than expected.Therefore,this study selected the backwater section of the Longbao River in the Wanzhou District of Chongqing City(Sluobao Community to Yinheshi Bridge Section)as the object.The length of the section is 3.6km,according to the dry season(March-May)and rainy season(May-October),backwater period(October-December),study the spatio-temporal variation characteristics and influencing factors of river water quality,use the comprehensive pollution index method and principal component analysis method to evaluate water quality,and analyze different river courses The pollution degree of the region and its main pollution factors are used to explore the source of pollutants through the analysis of sediment characteristics and the correlation analysis of river water quality and sediment composition;the MIKE21 model is used to analyze the transport and diffusion laws of river pollutants,and to study the river water environment and rainwater quality Relationship,identify the driving factors of river water pollution and the source of pollutants,and provide data support for river management in mountainous cities and the stable operation of sponge city systems.The main conclusions are:(1)The p H value of each point in the river channel detection is 6.63-8.01,the average p H in the dry season,rainy season and backwater period is 7.45,7.53,7.09;the average DO in the dry season,rainy season and backwater period is 7.72,8.27,7.13 mg,respectively./L;The TN concentration at each point of the river channel is 2.33-6.44mg/l,and the average concentration in the dry season,rainy season,and backwater period is 4.53,3.12,and 4.84 mg/L respectively,all exceeding the surface water category V water standards;dry season,rainy season,The average concentration of NH3-N in the backwater period is 2.35,1.79,2.52mg/L,which has reached or exceeded the standard of surface water type V;the TP concentration at each point of the river channel is 0.19-2.97mg/L,dry season,rainy season and backwater period The average concentrations are 0.9,0.36 and 0.74 mg/l,respectively,which are above the level Ⅴof the surface water;the COD value of each point of the river varies from 17 to 109mg/L,and the dry season,rainy season,backwater period 56.03,68.07,26.67 mg /l,the pollution is more serious in the dry and rainy seasons,exceeding the level Ⅴ of the surface water,and the water quality in the backwater period has improved to the levelⅣ of the surface water.From the perspective of the overall river course,the dry season,rainy season and backwater period showed a trend of gradually decreasing pollution.(2)The evaluation results of the comprehensive index of water quality show that:(1)The 1# point in the dry season is moderately polluted,mainly because the N,P pollutants and COD are all exceeded,and the NH3-N is exceeded in the 2# point;the4#-7# point river The section is severely polluted,with N,P pollutants and COD exceeding the standard;the single factor index of p H and DO shows that the backwater section of the Longbao River in the dry season has a good self-purification ability.(2)The river section at the 6#-7# point in the rainy season is heavily polluted,and the N,P pollutants and COD all exceed the standard;the pollution degree in the upstream of the backwater area is generally lower than that in the downstream;the average of the single factor index Pi and the average value of the comprehensive pollution index show that each of the rainy seasons The pollution degree of the monitoring point: 4#<5#<6#<7#.(3)The 1st point in the return water period is moderate pollution,mainly because the N and P pollutants exceed the standard,and the 2# point is TN exceeding the standard;the downstream is heavy pollution,mainly the N and P pollutants exceed the standard;the single factor index Pi It shows that the p H,DO,and COD indicators of the channel did not exceed the standard during the backwater period,and the channel maintained a certain self-purification capacity during the backwater period.Principal component analysis showed that:(1)The points 1#,4# and 5# in the dry season were seriously polluted by N element;the points 1#,4#,5# and 7# were seriously polluted by COD.(2)COD and N elements are more seriously polluted at the1#,6# and 7 points in the rainy season;the 2#,4#,6# and 7# points are significantly affected by P element and p H.(3)The 2#-4# points in the backwater period are more polluted.The 2#,4#,5# and 7# points are greatly affected by the N and P elements.(3)The pollutant components of the water body of the Longbao River in the dry season have a significant correlation with the sediment pollution source.The correlations are as follows: the correlation coefficients of COD in the water and the organic matter and total phosphorus in the sediment are: 0.82 and 0.62;TP and the bottom in the water Correlation coefficients of total phosphorus and total nitrogen in mud are 0.64 and 0.57respectively;correlation coefficients of TN and organic matter,total phosphorus and total nitrogen in sediment are 0.78,0.73 and 0.62 respectively.The TP in the rainy season water has a significant correlation with the release of total phosphorus in the sediment.The correlation is: the correlation coefficients of TP in the water and total phosphorus and total nitrogen are: 0.62 and 0.63,respectively.During the backwater period,each pollutant component of the water body has a significant correlation with the sediment pollution source.The correlation is as follows: the correlation coefficient of COD in the water and total nitrogen in the sediment is 0.84;the correlation between TP in the water and the organic matter,total phosphorus,and total nitrogen in the sediment The correlations are: 0.86,0.88,and 0.80;the correlations between TN and sediment organic matter,total phosphorus,and total nitrogen are 0.56,0.79,and0.73,respectively.Therefore,river pollutants come from the release of internal pollution and the import of external pollution.(3)The pollutant components of the Longbao River water body have a significant correlation with sediment pollution sources.The correlations are as follows:(1)The correlation coefficients between COD and organic matter and total phosphorus in sediment in the dry season are: 0.82 and 0.62;TP and bottom in water Correlation coefficients of total phosphorus and total nitrogen in mud are: 0.64,0.57;Correlation coefficients of TN and sediment organic matter,total phosphorus,and total nitrogen in water are: 0.78,0.73,0.62,respectively.(2)The correlation coefficients of TP,total phosphorus and total nitrogen in rainy season water are: 0.62 and 0.63 respectively.(3)The correlation coefficient between COD and total nitrogen in sediment during backwater period is 0.84;the correlation coefficient between TP and organic matter,total phosphorus and total nitrogen in sediment is 0.86,0.88 and 0.80;TN and organic matter and total phosphorus in sediment are respectively,The correlation coefficients of total nitrogen are: 0.56,0.79,0.73.Therefore,river pollutants come from the release of internal pollution and the import of external pollution.(4)The results of the MIKE21 hydrodynamic-convection-diffusion coupled water quality model show that the pollution of the Longbao River backwater area is less affected by the inflow of the screw package branch,and it is affected by three residential areas in Xujia Garden,the Three Gorges Vocational College,the commercial area,and the intersection of Longducha.The influence of the soluble pollutants brought by the rainwater discharge of the plot is small.The pollution sources of the water environment of the Longbao River return section are mainly endogenous pollution,rain overflow overflow pollution,buried river sewage pipeline leakage pollution,SS-based non-point source pollution caused by construction waste,and nitrogen and phosphorus elements.Agricultural non-point source pollution.(5)The management of sponge city and urban water environment in the backwater section of Longbao River has three main aspects:(1)Controlling endogenous pollutants by means of dredging,running water drainage,aeration and oxygenation,etc.,and improving the self-purification ability of river water bodies;(2)The sewage interception and control pipe controls the input of external pollutants and reduces the external pollution load of the water body;(3)Improve the "river length system" system and implement the monitoring and management of changes in the water environment.The objects that need to be monitored and managed in the Longbao River research section are: a,1# and 2# near the river channel,focusing on the water quality index of nitrogen and phosphorus element pollutants;b,2# point entrance 100 m to 5#downstream of the river Section,combined with the accumulation of sediment,focus on COD and N,P element pollutant indicators;c,5#-7# section,focus on N,P pollutants and COD indicators.Through the above three ways,we can better control the dynamic and self-purification ability of the Longbao River water environment,and can promptly warn and take emergency measures for sudden conditions and water deterioration. |
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