植被对绿色屋顶径流量和水质影响

植被是绿色屋顶的关键组成部分,也是影响绿色屋顶径流量和水质的重要因素之一.本文基于大花马齿苋(Portulaca grandiflora)、佛甲草(Sedum lineare)、高羊茅(Festuca elata)和无植被(对照组)这4种植被覆盖类型绿色屋顶2017年植物生长特征、降雨和径流过程的监测,及对雨水和各绿色屋顶径流中营养元素(NH_4~+-N、NO_3~--N、NO_2~--N和PO_4~(3-)-P)与重金属(Cr、Cd、Cu和Ni)的浓度检测,定量分析了不同植被覆盖类型对绿色屋顶径流量和污染负荷的影响.结果表明:①大花马齿苋、佛甲草、高羊茅和对照组绿色屋顶的平均径流削减率分别为51. 3%、41. 5%、36. 3%和33. 0%,大花马齿苋绿色屋顶径流削减率显著高于高羊茅和对照组绿色屋顶(P 0. 05);②大花马齿苋和佛甲草绿色屋顶是NH_4~+-N、NO_3~--N、NO_2~--N和PO_4~(3-)-P的汇,且地上生物量更大的大花马齿苋绿色屋顶对营养元素的污染负荷削减率(分别为59. 6%、99. 9%、82. 5%和25. 7%)均高于佛甲草绿色屋顶(分别为52. 5%、89. 3%、75. 3%和7. 8%),而高羊茅和对照组绿色屋顶是NH_4~+-N和NO_2~--N的汇,是NO_3~--N和PO_4~(3-)-P的源;③大花马齿苋、佛甲草、高羊茅和对照组绿色屋顶均是DCd的汇,污染负荷削减率分别为19. 2%、41. 5%、38. 4%和31. 1%,但4组绿色屋顶均是DCr、DCu和DNi的源.

Impacts of Vegetation on Quantity and Quality of Runoff from Green Roofs

As a key component of green roofs, vegetation may have significant impacts on both the quantity and quality of runoff. In this study, the effects of vegetation on both the quantity and quality of runoff from green roofs are investigated through monitoring the rainfall and runoff processes of green roofs with four different types of vegetation cover (Portulaca grandiflora, Sedum lineare, Festuca elata, and a non-vegetated bed as control) during 2017. The growth characteristics of the vegetation were also monitored, and the nutrients (NH₄⁺-N, NO₃^--N, NO₂^--N, and PO₄^3--P) and heavy metals (Cr, Cd, Cu, and Ni) in the rainwater and runoff were measured. The results show that the average rainfall event-based runoff reduction rates for the four green roof types were 51.3%, 41.5%, 36.3%, and 33.0%, respectively. Furthermore, the runoff reduction rates of the green roof planted with Portulaca grandiflora were significantly higher than both the Festuca elata green roof and the non-vegetated bed (P<0.05). The green roofs planted with Portulaca grandiflora and Sedum lineare both acted as sinks for the nutrients. The Portulaca grandiflora green roof, which had a higher biomass, provides higher nutrient load reduction rates (59.6%, 99.9%, 82.5%, and 25.7% for NH₄⁺-N, NO₃^--N, NO₂^--N, and PO₄^3--P, respectively) than the Sedum lineare green roof (52.5%, 89.3%, 75.3%, and 7.8%, respectively). The Festuca elata green roof and the non-vegetation bed acted as sinks for NH₄⁺-N and NO₂^--N but were sources of NO₃^--N and PO₄^3--P. All four of the green roofs were sinks for DCd, with pollution load reduction rates of 19.2%, 41.5%, 38.4%, and 31.1%, respectively. However, all the green roofs acted as the sources of DCr, DCu, and DNi.