Study On The Regulation Of Extensive Green Roof Plant Growth And Runoff Control Under The Climatic Characteristics Of Beijing

Under the influence of urbanization and climate change,problems such as rainfall infiltration decreasing,flood disasters,and rainfall runoff pollution frequently occur.As an important measure for low-impact development concepts,green roof has attracted wide attention due to its ecological and environmental benefits.This study focused on the three main contents:Beijing’s green roof plant growth physiology,rainfall runoff water volume control,and water quality effect from interactive research.It also evaluated and recommended the selection of materials suitable for each structural layer under the climatic characteristics of Beijing,and provided experimental basis for the construction of the development of green roofs in Beijing and the regions with similar climatic characteristics.The conclusions of this paper were as follows:（1）The growth adaptabilities of five typical sedum species manifest as:Sedum lineare Thunb.>Sedum aizoon L.>Sedum spectabile.>Sedum sarmentosum Bunge>Sedum spurium“Coccineum”.There is a strong correlation between plant height,vegetation coverage and temperature,rainfall frequency,but there is no significant correlation with rainfall depth,and there is a strong correlation between plant height and vegetation coverage.The type of substrate is the main factor affecting the growth of plants.When there are more organic fertilizers on the substrate,the plants grow better.Large-scale green roof modules can make the plants have a stable growth environment and the plants grow better.Under drought stress,according to the changes of the plant’s external morphology and physiological characteristics,and comprehensive analysis with membership function,the drought resistance of five sedum species was as follows:Sedum spectabile.>Sedum aizoon L.>Sedum lineare Thunb.>Sedum sarmentosum Bunge.>Sedum spurium“Coccineum”.（2）There are no significant differences in the retention effect of green roofs by different planting methods,planting coverage,slopes and drainage layer materials.The plant species have a significant effect on the retention capacity of green roofs.The retention effects of Sedum lineare Thunb.and Sedum spectabile.are better.The stagnation effects of Sedum aizoon L.and Sedum spurium“Coccineum”are normal.For the same green roof module,the retention effect at 1 year of operation is significantly different from the retention effect at 2and 3 years of operation.In addition,the difference in rainfall levels and seasonal months have significant differences in the retention of green roofs.According to the cluster analysis and verification,the green roof with larger installation scale and deeper substrate thickness has obvious advantages in retaining effect,while the substrate layer is ultra-lightweight substrate or the vegetation layer is Sedum spurium“Coccineum”/Sedum aizoon L.or the drainage layer is porous.The retention effect of the green roof of fiber cotton is the most common.（3）Study on the control effect of the green roofs on pollutants shows:the average reduction rate of SS for 10 types of EGR modules is 79.57%.The green roof with a short running time does not remove SS as well as the green roof with a long running time.Increasing the scale of the module can increase the stability of the SS removal effect of the green roof.And increasing the scale of the module and the thickness of the substrate can improve the removal effect of nitrogen by the green roof,but have no effect on the removal of phosphorus.The type of substrate would affect the TP concentration and load reduction effect of the green roof runoff,but it could affect the concentration and removal of nitrogen.Matrix type will affect TP concentration and load reduction effect of green roof runoff,but there is no difference in nitrogen concentration and load removal effect.The green roof with a short running time easily to become the release source of TP,and the season varion will affect the nutrient concentration of the green roof runoff.Generally,the concentrations of TN,NO₃^--N and TP in spring runoff are higher,and the concentrations in summer and autumn are higher.The NH₄⁺-N concentration is higher in autumn runoff.The green roof is a sink of heavy metal Zn.During the monitoring period,the average removal rate of Zn for 13 types of EGRs was68.23%.The removal effect of Zn from green roofs with short running time is not as good as that of green roofs with long running time.（4）Study on the control effect of the green roofs on organic pollutants shows:the green roof is a source of runoff organic pollutants.Green roofs with a short running time will emit high concentrations of COD and TOC,and the organic matter concentration is low when the matrix layer is ultra-lightweight matrix.The DOM components in green roof runoff are mainly fulvic acid-like and tryptophan-like protein substances.The peak fluorescence intensity of fulvic acid classified by DOM group has a good correlation with TOC and COD concentrations.Eight types of green roof runoff pollutant indicators can be divided into four categories after the principal component analysis.（5）Sedum spectabile.,Sedum lineare Thunb.and Sedum aizoon L.are recommended plants for the selection of vegetation layers of the green roofs.Sedum spurium“Coccineum”should not be used as a recommended species for the selection of rain-flooding green roof vegetation layers in Beijing.The green roofs are suitable for the environment with a roof slope of 12°and below,and have good running status under actual surroundings.When the extensive green roofs were used in actual engineering and when the site conditions permit,It can consider increasing the size of the green roof module scale to increase the stability of the green roofs during operation;under the condition of meeting the roof load,usually the thickness of 150 mm substrate is suitable;under the condition of sufficient budget,it can consider using porous wool fiber as the drainage layer material and the bumpy plastic drainage board is better than the ceramsite drainage layer material choice.In addition,ultra-lightweight substrate should not be used as the preferred type of green roof substrate type.It is applicable under the premise that the roof bearing capacity is very weak and other matrix types cannot meet the load.