海绵城市试点区域内面源污染发生过程及其对水体污染负荷贡献评估

低影响开发(LID)作为我国海绵城市建设中最为重要的技术手段,能够有效解决大概率小降雨事件带来的径流污染问题,然而海绵城市试点区域内城市面源污染的发生全过程与污染输出特征规律鲜有报道.本研究选择已经建成的海绵城市建设试点区域,在地块尺度上研究多个不同降雨事件中城市面源晴天污染物累积量、降雨径流冲刷量、LID削减量、外排后对河流水体的污染输出量.结果表明,LID建设区域内街尘的累积范围为7.82~33.36 g·m-2,降雨冲刷量为0.29~4.90 g·m-2,街尘的径流冲刷率为0.9%~62.7%;LID设施对降雨冲刷的固体悬浮物(SS)削减率达90%,即占街尘累积量的13.1%~16.7%,发生溢流时SS输出量占街尘累积量的0.6%~3.8%,占径流冲刷量的3.9%~5.0%.LID径流的调蓄能力大于其设计降雨量(即在降雨量为21 mm)时径流无外排,经过LID设施外排径流水中COD、NH+4-N、TN、TP浓度均低于《地表水环境质量标准》(GB3838—2002)Ⅳ类水标准.另外,LID设施对颗粒物中小于10μm和大于250μm的细颗粒物去除率较高,且微地形和常规性清扫(人工清扫和机械清扫)均对城市面源污染物累积和迁移分布产生影响.上述发现揭示了LID建设区域内城市面源的发生规律,可为定量评估LID工程绩效提供科学依据.

The contribution of urban diffuse pollutants to water pollution in a sponge city pilot area

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 RDS that accumulated during dry weather ranged from 7.82 to 33.36 g·m^-2. The amounts of sediment washed off during rainfall events ranged from 0.29 to 4.90 g·m^-2, and accounted for between 0.9% and 62.7% of the accumulated RDS. By passing through the LID facilities, the SS in surface runoff decreased by up to 90%, which accounted for between 13.1% and 16.7% of the accumulated RDS. The SS in discharge water that passed through LID facilities accounted for between 0.6% and 3.8% of the accumulated RDS, and for between 3.9% and 5.0% of the amount washed off. The LID facilities met the standard for their design rainfall. The concentrations of COD, NH₄⁺-N, TN, and TP that passed through the LID facility were lower than the Class IV national surface water standards (GB3838-2002). The LID facility also selectively removed different SS particles from runoff water. Factors such as micro-topography and street cleaning also influenced the accumulation and flushing of RDS. The findings from this study about the transport of diffuse pollutants in a sponge city test area will support quantitative evaluations of the performance of LIDs.