| As a low-impact development infrastructure,green roof is a nature-based solution to various“urban diseases”caused by urban development related to rainwater problems.With the development of integrated urban water management in various countries around the world and the upsurge of China’s sponge city construction,it has been widely used in urban construction because of its numerous economic,ecological and environmental benefits.The green roof includes vegetation layer,substrate layer,drainage layer,filter layer,and root-blocking waterproof layer.The substrate layer is the main structural layer in the green roof system.It not only provides growth space for plants,but also has the effect on rainfall runoff and water quality.Therefore,the selection of green roof planting substrates needs to take into account many principles and requirements.This research is aimed at extensive green roofs,based on the research that the author’s team has used a certain ultra-lightweight clean substrate and an improved soil as the substrate on the impact of green roofs on rainfall runoff and quality,ten materials are used to make seven kinds of improved soil.By green roof moudles with that as substrate and artificially simulating the 1,3 and 5 year occurrences in Beijing,the rainfall duration is 1 hour rainfall,and the effects of green roofs with different matrix ratios substrate on rainfall runoff retention and runoff quality were studied,provide technical support for more selection of green roof substrates.Simulated soil columns experiment were conducted to study the leaching characteristics of nitrogen and phosphorus nutrients in different ratios of substrates under three-year rainfall,to understand the impact of green roof substrate leaching on rainwater runoff.The main research conclusions are as follows:（1）The average rainfall retention rate of the seven green roofs with different substrates is between（40.61%±4.36%）-（58.60%±5.63%）,and the runoff coefficient is between（0.41±0.06）-（0.59±0.04）.The green roof with substrates pastoral soil:lightweight aggregate=1:1 and light sandy loam:humus soil:perlite:vermiculite=2.5:5:2:0.5 has the worst effect on rainfall runoff retention,while the matrix ratio of green roof substrate is leaf mould:vermiculite:sand=7:2:1 retention effect is the best.With the increase of the rainfall return period,the runoff yield of green roofs increased,the rainfall return period increased from once in 1 year to once in 3 years and once in 5 years,and the average runoff yield on green roofs increased 23.11%and 73.78%.（2）SS concentration of green roof runoff increases with the increase in the return period of rainfall.Compared with normal roof,green roofs can reduce the runoff SS concentration and load to a certain extent.However,the green roof is the source of pollutants such as COD,NH4+-N,NO3--N,TN,and TP.The concentration and load of runoff pollutants are greater than those of normal roof.The green roof moudle with the substrate as pastoral soil:lightweight aggregate=1:1 has the best runoff quality,and the substrate ratio are light sandy loam:humus:perlite:vermiculite=2.5:5:2:0.5 and leaf mould:vermiculite:sand=7:2:1 green roofs runoff quality are the worst.（3）In the soil column leaching experiment,the concentration of nitrogen and phosphorus in the leaching solutions decreased with the increase of experiment times,and then gradually stabilized.The leaching amount of nitrogen and phosphorus in the first three experiments accounted for 62.8%-79.9%of the total leaching amount.The leaching amount of TP is less than that of TN,and the amount of leaching of NO3--N is much greater than that of NH4+-N,which is the main form of nitrogen leaching.The green roof substrate without adding nutrient soil has the lowest risk of nitrogen and phosphorus leaching.Adding sandy loam increased the amount of phosphorus leaching.When leaf mould or humus soil accounts for a relatively large amount,the amount of nitrogen and phosphorus leaching was high.Therefore,it is not recommended to use them as the main materials of green roof substrate.（4）It is recommended to use pastoral soil as the main material of green roof substrate,adding appropriate amount of turf or pine needles as nutrients,and adding a small amount of vermiculite and perlite to improve the soil structure. |
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