Impact Of Lid On Non-point Source Pollution And Control Of Water Quality And Quantity In Spongy City Pilot Areas

Low-impact developments?LIDs?,an important component of sponge city developments,can effectively control the loads of pollutants transported in runoff during high frequency small rainfall events.Few studies have reported how diffuse pollutants contribute to water pollution in experimental sponge cities.In this study,we quantified the amount of road-deposited sediment?RDS?that accumulated during dry weather,the amount of SS that was washed off during rainfall events,the reduction in SS because of LID facilities,and the amounts discharged through LID facilities in a sponge city trial area.The polluting process and the runoff control effect were assessed preliminarily and the results are as follows:1.The RDS accumulation range in major traffic roads and factory parks in the LID construction area was within 7.82 to 33.36 g·m^-2 and 5 g·m^-2,respectively,which was significantly lower than the traditional major traffic roads and factory parks.From the state of street dust standing on the underside of the road,the mass per unit area of RDS in the free state was 4.2 to 4.7 times that of the fixed state.The pollutant load carried by the traffic road pavement and street dust in the factory park is: TN,36.23⁶9.29mg·kg^-1 and50.2²82.6mg·kg^-1;TP,328.67⁷88.65mg·kg^-1 and 289.4⁵73.4 Mg·kg^-1;2.In the LID construction area,the amount of street dusty rainy days in major traffic roads and factory parks was 0.29 to 4.90 g·m^-2 and 0.05 to 0.12 g·m^-2,respectively,and the erosion rates were 2.14% to 21.76% and 15.9% to 43.4,% respectively.%,accounting for 3.7%¹4.7% of street dust accumulation and 1.0%².4%;pollution load for scouring:TN,10.4¹6.12mg·kg^-1 and 14.9⁸9.3mg·kg^-1;TP,21.79¹62.96 mg kg^-1 and 91.1^-141.8mg kg^-1.3.LID has obvious effects on runoff pollution at the scale of plots,and no overflow occurs when the rainfall is less than 21 mm.The concentration of COD,NH₄⁺-N,TN,and TP in the effluent water passing through the LID facility during overflow was lower than the Class IV water standard in the Environmental Quality Standard for Surface Water(GB3838^-2002).TN pollution load accounted for 8.1%¹2.5% of the flushing load,1.9%³.6% of street dust cumulative load,TP pollution load accounted for0.06%⁰.46% of the flushing load,and accounted for the street dust cumulative load of0.01%⁰.03%.4.The above results quantitatively characterize the four processes of mass pollution,rainfall,runoff flushing,LID purging,and pollution output during overflow in urban areas on different scales of rainfall events,which can provide scientific basis for LID project performance evaluation.