基质类型及厚度对绿色屋顶径流量和水质影响

Impacts of types and depth of substrates on quantity and quality of runoff from green roofs

绿色屋顶是海绵城市建设的重要措施之一,近年来逐渐得到广泛应用。通过对比北京市3种生长基质类型(田园土、改良土和轻质基)和2种基质厚度(15和10 cm)共6个佛甲草(Sedum lineare)绿色屋顶在2017年降雨和径流过程、雨水和径流中营养元素(NH_(4)^(+)-N、NO_(3)^(-)-N、NO_(2)^(-)-N和PO_(4)^(3-)-P)与可溶性重金属(DCr、DCd、DCu和DNi)的监测数据,定量分析基质类型和厚度对绿色屋顶径流量和水质影响。结果表明:1)田园土和改良土绿色屋顶径流削减率显著高于轻质基绿色屋顶(P<0.05),基质厚度为15 cm的田园土、改良土和轻质基绿色屋顶的平均径流削减率(分别为67.8%、60.3%和46.6%)均明显高于基质厚度为10 cm对照组(分别为55.6%、53.0%和41.5%)。2)实验绿色屋顶均是NH_(4)^(+)-N、NO_(3)^(-)-N和NO_(2)^(-)-N的汇,平均污染负荷削减率分别为(86.8±15.6)%、(69.4±17.1)%和(58.5±24.1)%。基质厚度15 cm的改良土和基质厚度10 cm的轻质基绿色屋顶是PO_(4)^(3-)-P的汇,污染负荷削减率分别为21.8%和7.8%,但其他4个绿色屋顶均为PO_(4)^(3-)-P的源。3)实验绿色屋顶均是DCd的汇,平均污染负荷削减率为(52.4±8.8)%,除基质厚度为15 cm的改良土绿色屋顶是DCr的汇(污染负荷削减率为18.6%),其他5个绿色屋顶均是DCr的源,所有绿色屋顶均是DCu和DNi的释放源。研究结果可为我国北方城市绿色屋顶的径流水质评估和基质比选提供科学依据。

[Background]As an important measure of sponge city,green roofs have been wildly adopted in urban water resource management in recent years. However,few researches focus on both water quantity and quality of green roof runoff in North China. Substrate is one of the key components of green roofs,thus it is important to clarify how substrate influences runoff quantity and quality from green roof.[Methods]We set up 6 extensive green roofs with 3 types( i. e.,local planting soil,engineered soil,and light growing medium) and 2 depths( 15 cm and 10 cm) of substrates in Beijing. In order to analyze the influences of type and depth of substrates on the water quantity and quality of green roof runoff,we used a weather station( HOBO U30) and rain gauges to monitor the rainfall and runoff processes of green roofs under natural rainfall conditions during the rainy season in 2017. The nutrients( NH_(4)^(+)-N,NO_(3)^(-)-N,NO_(2)^(-)-N and PO_(4)^(3-)-P) and dissolved heavy metals( DCr,DCd,DCu,and DNi) in the rainwater and runoff were analyzed by Automatic Discrete Analyzer( SmartChem 200) and ICP-MS. [Results]1) The average runoff reduction rates of green roofs with local planting soil and engineered soil were significantly higher than the that of green roofs with light growing medium( P < 0. 05). The local planting soil,engineered soil and light growing medium green roofs with a substrate thickness of 15 cm provided higher runoff reduction rates( 67. 8%,60. 3%,and 46. 6%,respectively) than the those with a substrate thickness of 10 cm( 55. 6%,53. 0%,and 41. 5%,respectively). 2) The experimental green roofs were the sinks of NH_(4)^(+)-N,NO_(3)^(-)-N and NO_(2)^(-)-N,the mean pollution load reduction rates were( 86. 8 ±15. 6) %,( 69. 4 ± 17. 1) % and( 58. 5 ± 24. 1) %,respectively. The engineered soil green roof with a substrate thickness of 15 cm and the light growing medium green roof with a substrate thickness of 10 cm were the sinks of PO_(4)^(3-)-P,the reduction rates of pollution loads were 21. 8% and 7. 8%,respectively,but the other green roofs were all the sources of PO_(4)^(3-)-P. 3) The experimental green roofs were the sinks of DCd,and the mean reduction rate of pollution load was( 52. 4 ± 8. 8) %. Except for the engineered soil green roof with a substrate thickness of 15 cm was the sink of DCr( the reduction rate of pollution load was 18. 6%),the other 5 green roofs were all the sources of DCr,and all of the 6 experimental green roofs were the sources of DCu and DNi. [Conculsions]The runoff reduction rates of local planting soil and engineered soil green roofs are significantly higher than that of the light growing medium green roofs. Green roofs with 15 cm depth have better performance in runoff management than green roofs with10 cm depth. The substrate type and depth also affect pollution loads in runoff from green roofs,and all the 6 experimental green roofs were the sinks of NH_(4)^(+)-N,NO_(3)^(-)-N,NO_(2)^(-)-N,and DCd,but were the sources of DCu and DNi. The results of this experiment provide scientific reference for the water quality evaluation and hydrologic design of green roofs in North China.