The Effect Of Extensive Green Roofs With Various Plant Species On Runoff Reduction And Purification

Green roof is one of the main contents to construct sponge city,which can reduce the runoff efficiently and improve runoff quality.Planting substrate and plant species of green roof are two decisive factors for runoff reduction and purification.Most of the previous studies were focused on the role of planting substrate of green roof on the rainwater reduction and purification,the contribution rates of different plants are largely unknown.This study selected commonly used two succulents（Sedum lineare and callisia repens）and four turfgrasses（Agrostis stolonifera,Lolium perenne,Festuca arundinacea,Poa pratensis）as the plants layer of green roofs,measuring plants contribution rates of runoff reduction under different rainfall intensities and different slopes,analyzing the rainwater purification ability of different green roofs.The results are as follows:（1）Plant species significantly affected the ability of extensive green roof to reduce runoff.Festuca arundinacea showed the largest runoff reduction ability in the four seasons,followed by Poa pratensis,Lolium perenne and Agrostis stolonifera.Two succulents（Sedum lineare and callisia repens）showed the worst runoff reduction ability.Path analysis showed that the runoff reduction rate of extensive green roofs was mainly affected by plant shoot biomass and evapotranspiration with direct correlation coefficients of 0.990 and 0.846,respectively.（2）Green roof usually has a certain slope,and the different slopes will also affect the ability to reduce runoff.The greater the slope,the smaller the green roof runoff reduction ability.Different plant species have significant differences on the contribution of green roof runoff reduction.When rainfall intensity was below 50mm/d,Festuca arundinacea had significant contribution in runoff reduction.When rainfall intensity was below 25mm/d,Poa pratensis,Lolium perenne and Agrostis stolonifera also had significant contribution in runoff reduction.When rainfall intensity was below 10mm/d,two succulents（Sedum lineare and callisia repens）had significant contribution in runoff reduction.（3）There are significant differences in the rainwater purification ability of different plant species to extensive green roof.The three turfgrasses showed significantly higher ability of absorbing and purifying nutrients for rainwater than two succulents.Different turfgrasses have significantly different ability of absorbing and purifying for different nutrients in rainwater,the order of purification for TN、NH₄-N、NO₃-N and COD is Festuca arundinacea>Poa pratensis>Lolium perenne,but the purification ability of TP and PO₄-P is Lolium perenne>Festuca arundinacea>Poa pratensis.The absorption and purification ability of two succulents to TP、PO₄-P、TN、NH₄-N and NO₃-N were low.