| In the process of rapid urbanization development,a series of ecological and environmental problems have been highlighted.In order to solve the contradiction between“economic-social-environment”,targeted urban management strategies have been proposed all over the world.As far as mountainous cities are concerned,the unique slope,underlying surface and land use conditions lead to higher non-point source pollution load,which makes the water environment quality decline sharply and affects the city's sustainable development capability.In order to solve this problem,this paper took the atmospheric environment and typical underlying surface?mountain urban roads,parks,public buildings and residential quarters?in the non-point source pollution control area of Chongqing Yuelai New City as the research object,researched the monitoring area and monitoring points,and divided the urban surface source water collection unit according to the topography and drainage system status.Then automatic and manual sampling monitoring and indoor analysis combined methods were used to determine pollutant parameters and dry and wet deposition of urban non-point source pollution in mountainous cities.Furthermore,the runoff and pollutant migration and transformation laws of the“production-sink-flow-stagnation-discharge”process in mountainous cities were studied.It aimed to provide data support and theoretical basis for the development of technical solutions for non-point source pollution control and stormwater control projects.The main conclusions are as follows:?1?The air quality of Chongqing Yuelai New City was significantly seasonally affected by factors such as temperature and wind speed,and it had a strong correlation with atmospheric dry and wet deposition pollutant flux.From the perspective of air quality,PM10 and PM2.5 daily average concentration pollution dominated,followed by NO2.From the influencing factors,the concentrations of atmospheric pollutants were significantly negatively correlated with temperature and ambient wind speed.The influence of atmospheric pressure on the concentration of atmospheric pollutants outside the spring season was negligible.In addition,the main component of nitrogen in the atmospheric particle suspension of Yuelai New City was inorganic nitrogen?NO3-+NH4+?;the concentration of TP was two orders of magnitude lower than the concentration of TN.Atmospheric nitrogen deposition was dominated by wet deposition,accounting for 61.24%of total sedimentation flux;phosphorus deposition was dominated by dry deposition,accounting for 52.25%of total sedimentation flux.The sedimentation fluxes of NO3--N,NH4+-N,TN,TP and ON in atmospheric wet deposition are 7.55,11.88,21.85,0.81,2.42 kg/?hm2·a?,and the sedimentation fluxes of NO3--N,NH4+-N,TN,TP and ON in atmospheric dry deposition are 4.26,6.39,13.83,0.88,3.17 kg/?hm2·a?,respectively.?2?Rainfall runoff pollutants in mountainous urban roads were affected by many factors such as rainfall intensity,slope and catchment area.Firstly,because the erosion effect of rainfall runoff in the event of small rainfall intensity was higher than the dilution effect of rainfall,the pollutant concentrations were significantly higher than that in the medium and large rainfall intensity events,but the peak of pollutants appeared at the initial time of rainfall and 1020min after the rainfall peak value.It was seen that NH4+-N was the main form of TN in the channel flow water,while the concentration of NO3--N was low.Secondly,the greater the slope of mountainous urban roads,the more obvious the initial flushing effect,the worse the soil permeability of the bioretention zone along the roadside,and the overall first flush effects were characterized by TN>TSS>COD>TP,so it was recommended to control 30%40%FF value.In addition,when the rainfall intensity was constant,the channel flow rate was not only related to the slope,but also had a strong correlation with the catchment area.?3?The trend of pollutants such as TSS,COD and TP in the runoff of the Exhibition Park?typical mountain park?was similar to that of mountainous urban roads,but the volatility of TN and chlorophyll a were strong,among which NO3--N was the main form of TN in park runoff rainwater,accounting for 42%65%,while the concentration of NH4+-N was relatively low.The rainfall runoff in the park was greatly affected by the rainfall intensity,but the peak flow had a significant hysteresis compared with the peak rainfall.In addition,the rainfall runoff in the park only had a flush effect when the rainfall intensity was high,and it was basically consistent with the first flush effect of road pollutants.?4?Rainwater runoff organization in public buildings and residential communities in mountainous cities is particularly important.The water quality of the 6 rainwater storage tanks of the International Expo Center?typical public buildings?and the 5rainwater storage tanks of the residential quarters all met the road cleaning and urban greening water standards in?Urban Wastewater Recycling Urban Miscellaneous Water Quality??GB/T 18920-2002?.There were different sources of nitrogen and phosphorus pollutants in International Expo Center and residential quarters,among which residential areas were mainly granular nitrogen and phosphorus,while the sources of nitrogen and phosphorus in International Expo Center were more complicated.At the same time,due to the difference in catchment area of rainwater storage tanks and the difference in the proportion of impervious catchment area,the reuse rate of Yubo Center's rainwater storage tanks were significantly higher than that of residential quarters.?5?The pollution load flux and annual average load level of the underlying surface?urban roads,parks,public buildings and residential areas?of the three typical mountain cities were quite different.The pollution load fluxes of TSS,COD,NO3--N,NH4+-N,ON,TN and TP in mountainous city roads were 3120.31,567.35,9.94,10.04,5.27,25.28and 5.54 kg/?hm2.a?,respectively.The pollution load fluxes of TSS,COD,NO3--N,NH4+-N,ON,TN,TP and chlorophyll A in mountain city park were 456.15,226.95,3.37,4.13,1.06,8.56,1.10 and 0.06 kg/?hm2.a?,respectivel.The pollution load fluxes of TSS,COD,NH4+-N,TN and TP in public buildings were 576.63,37.12,8.55,26.33 and0.68 kg/?hm2.a?,respectively.The pollution load fluxes of TSS,COD,NH4+-N,TN and TP in residential area were 559.82,21.05,1.17,17.74 and 1.13 kg/?hm2.a?,respectively.?6?The total amount of non-point source pollution in Chongqing Yuelai New City was mainly atmospheric dry deposition,but the main direct input source of non-point source pollution was rainfall runoff.Although the surface water environment of Yuelai New City had reached the water function zoning requirements approved by Chongqing Municipality.As an important factor affecting the quality of water environment,non-point source pollution still needs to adopt corresponding technical measures and policy guidance to deal with this threat. |
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