Effect Of Light Green Roof Substrate And Plant Combinations On Rainwater Runoff Quality

Green roof plays an important role in rainwater management,which can not only alleviate the pressure of drainage pipes,reduce flood disasters,but also purify the pollution of rainwater runoff on the roof,thus collecting and utilizing rainwater and alleviating the pressure of water use.It has become an important part of creating a sustainable city,and it is of great significance to study the influence of plant species,substrate species and their interaction on the quality of rainwater runoff.The purpose of this study is to maximize the purification effect of the combination of green roof and planting through the reasonable and scientific combination of substrate and lawn grass,and to save economic and time costs for the combination of substrate and vegetation in the future urban green roof construction.This study is divided into two experiments.The first is the experiment of four substrates without vegetation cover.The experimental materials are four substrates（A peat soil:perlite:vermiculite=5:3:1:1,B peat soil:vermiculite:perlite:zeolite=5:2:1:1,C peat soil:perlite:vermiculite:wheat straw and D garden soil）.The second is a sixteen-plant combination experiment with vegetation cover.Four kinds of turfgrass（1 Cynodondactylon:Zoysia japonica:Lolium perenne=7:2:1,2 Poa pratensis:Agrostis matsumurae Hack:Lolium perenne=5:4:1,3 Poa pratensis:Festucaelata Kengex:Lolium perenne=5:3:2,4 Zoysia japonica:Cynodondactylon=2:1）In both experiments,the height of substrates was set at 15cm.After a series of measurement,observation and data statistics,the pollutant concentrations of COD,TP,NH₄⁺-N,SS and TN in runoff of different substrates and planting combinations were obtained.According to the index measurement results,the four substrates and sixteen planting combinations were comprehensively evaluated by variance analysis and inverse membership function method.The research results show that:（1）As far as the effluent quality is concerned,there are significant differences between different substrates without vegetation coverage and the combination of green roof and planting with vegetation coverage in the purification capacity of rainwater runoff.Four substrates and sixteen combinations of planting have good purification effects on NH₄⁺-N and SS,but the concentrations of TP,TN and COD in the effluent have increased significantly,showing as pollution sources.（2）Among the four substrates,substrate A（soil:peat soil:vermiculite:perlite=5:3:1:1）with the highest proportion of peat soil has the worst effluent quality,while substrate D（garden soil）has the best effluent quality,indicating that the higher the proportion of nutrient substrates in different substrates,the higher the concentration of pollutants released by leaching in runoff and the worse the effluent quality.（3）Substrate B（garden soil:peat soil:perlite:zeolite:vermiculite=5:2:1:1:1）is a good growth substrate for green roof,and its effluent quality is second only to that of substrate D,and the planting combination with four kinds of grass can play a stable purification effect,and the range of grass species can be matched widely,showing a certain tolerance.（4）The reduction rate of NH₄⁺-N and SS pollution concentration in the planting combination with vegetation cover is higher than that in the substrate group without vegetation cover,which shows that turfgrass can enhance its pollution purification effect in the green roof system.A2（A garden soil:peat soil:vermiculite:perlite=5:3:1:1 and 2 Poa pratensis:Agrostis matsumurae Hack:Lolium perenne=5:4:1）performed best,while C1（C garden soil:peat soil:vermiculite:wheat straw:perlite=5:2:1:1 and 1 Cynodondactylon:Zoysia japonica:Lolium perenne=7:2:1）performed the worst.