城市不同下垫面的降雨径流污染

当点源污染被有效控制后,面源污染成为城市水质恶化的主要原因之一。屋面和路面等不透水面以及绿地是城市的3种主要下垫面形式。当暴雨产生时,各种下垫面特别是屋面和路面上汇聚大量污染物质产生径流,对城市生态环境造成严重的污染。以文教区为例,对屋面、路面、草坪的径流水质进行了监测,指标包括pH、悬浮固体(SS)、化学需氧量(COD)、总氮(TN)、总磷(TP)和生化需氧量(BOD5)等。比较分析发现,3种下垫面类型的径流水质均较差,COD、TN、TP、BOD5平均浓度超过地表水环境质量Ⅴ级标准。COD、TN和TP浓度与SS含量之间相关性较好,相关系数可达0.85以上。径流中污染物浓度受多个因素的影响,其中降雨量和降雨强度是两个重要因素,雨强越大,雨水对城市下垫面的冲刷就越强;在相同的污染物累积量条件下,降雨量越大,径流中污染物浓度越低。

Chemical analysis on stormwater-runoffpollution of different underlying urban surfaces

Diffuse pollution is one of the main sources that cause the deterioration of urban water quality after the point pollution is controlled effectively.Underlying surfaces such as roofs,roads,and lawns are the main types of surfaces found in city.During storm events,large amounts of pollutants deposited on the surfaces,especially roofs and roads,adding significant pollution to urban ecological environments.For this study,the quality of the three kinds of runoff was monitored in Beijing's university district,where indices included pH,suspended solids,chemical oxygen demand,total nitrogen,total phosphorus,biochemical oxygen demand,and so on.The pollution of the runoff is serious on all three of the underlying surfaces.COD,TN,TP and BOD_5 concentrations all exceed the fifth level of the environmental quality standards for China.In a correlation analysis,the correlation coefficients between COD,TN,TP concentration and SS content are all larger than 0.85.Findings suggest that there are many factors influencing the quality of runoff,with rainfall amount and intensity being two important factors.In addition,higher intensity can cause sharper flush on the surfaces,and concentration of pollutants decline in storms of larger amount of precipitation in relation to the same previous deposition of pollutants.