南宁市老城区降雨径流溯源及污染特征分析

Analysis on the Source Tracing and Pollution Characteristics of Rainfall Runoff in the Old Urban Area of Nanning City

降雨径流是城市河道污染的重要来源之一.为了解降雨径流的污染特征,对南宁市老城区进行降雨径流同步采样监测,分析不同降雨条件下不同下垫面污染状况、初期冲刷效应及污染贡献比等特征,探讨了径流污染初期冲刷计算方法及影响因素分析,并根据老城区菜市场下垫面讨论降雨径流下垫面选取标准与必要性.结果表明,南宁市老城区径流污染中,道路及菜市场的COD和TSS场次降雨径流平均浓度(EMC)大于绿地和屋顶,营养盐污染物EMC值由大到小依次是菜市场、绿地、屋顶和道路.大雨条件下各下垫面均有较为明显的初期冲刷效应,初期冲刷系数(b)均值为0.67,道路和绿地初期输送污染物较多;小雨和中雨条件下总体未产生明显的初期冲刷效应,b均值分别为0.83和0.94,评价冲刷效应更倾向于选取采用全过程计算的b值.基于多元统计分析表明,道路径流TSS的EMC值与总降雨历时之间呈显著正相关,绿地径流TN的EMC值与平均降雨强度间呈显著负相关.是否考虑菜市场作为下垫面的一类对营养盐污染负荷计算结果影响较大,对COD和TSS负荷计算结果几乎无影响,大雨下营养盐污染负荷差值百分比达80%,此时道路和菜市场污染物EMC差值百分比达到1012%.

Rainfall runoff is one of the important sources of urban river pollution.In order to understand the pollution characteristics of rainfall runoff,the synchronous sampling and monitoring of rainfall runoff in the old urban area of Nanning were carried out;the pollution condition,initial scouring effect,and pollution contribution ratio of different underlying surfaces under different rainfall conditions were analyzed;and the calculation method and influence factor analysis of initial scouring of runoff pollution were discussed.According to the underlying surface of the vegetable market in the old urban area,the selection standard and necessity of the underlying surface of rainfall runoff were discussed.The results showed that the average concentration(EMC)of COD and TSS in roads and vegetable markets were greater than those in green spaces and roofs in the runoff pollution of the old urban area of Nanning,and the EMC values of nutrient pollutants in field rainfall runoff were ranked in decreasing order as vegetable markets,green spaces,roofs,and roads.Under the condition of heavy rain,each underlying surface had an obvious initial scouring effect,the average value of initial scouring coefficient(b)was 0.67,and there were many pollutants transported by roads and green spaces at the initial stage.Under light rain and moderate rain conditions,there was no obvious initial scouring effect,and the average b values were 0.83 and 0.94,respectively.The b value calculated by the whole process was preferred for evaluating the scouring effect.Based on multivariate statistical analysis,the EMC value of TSS in road runoff was significantly positively correlated with the total rainfall duration(RD),and the EMC value of TN in green land runoff was significantly negatively correlated with the average rainfall intensity(ARI).Whether the vegetable market was considered as the underlying surface had a great impact on the calculation results of nutrient pollution load but had little impact on the calculation results of COD and TSS load.The difference percentage of nutrient pollution load under heavy rain reached 80%.Under this condition,the difference percentage of pollutant EMC between the road and vegetable market reached 1012%.