| As a new technology,green roof has been extensively applied.Especially with the increasing number of urban buildings,roof area also expand.Making full use of the roof resources will be the hotspot of urban ecological research.In recent years,there are more and more researches on roof greening.The main research focuses on the allocation of roof plants,the effect of roof greening on the cooling of buildings,the influence of different kinds of additives on the roof rainfall runoff and the biodiversity of the roof biological community.Biochar,as an effective additive to improve the ecological environment of the earth,has been proved to play a great role on ecology.It can fix organic matter by pyrolysis to achieve carbon sequestration and emission reduction in soil,and it is good for various soil properties and biological properties after being applied to the soil.Although biochar is widely used on the ground(farmland and forest),it has not been studied in detail on roof.Because of high temperature in summer,low temperature in winter,drought and low nutrient,large temperature difference between day and night,and the limited bearing capacity of buildings,it makes the key structure(substrate)of green roof is limited.So the use of additives in roof greening is the most direct and effective way to improve the roof ecological benefit.Compared with vermiculite,coal cinder,brick and sludge,biochar not only has the function of improving the properties of various soil,but also can improve the characteristics of microorganism and plant and fixed a large amount of carbon directly and indirectly,so it is a potential modifier for roof greening.Therefore,the application effect of five kinds of concentration gradient biochar treatment in roof greening was studied in this thesis.The effect and law of biochar on the improvement of physical and chemical properties and biological properties of the roof soil were expected to get the optimum proportion of biochar on roof and the effect of improving the green ecological benefits of roof.It provides reference for the application of biochar on roof greening.Our main results were as followed:1.Biochar can effectively reduce the density of roof substrate,increase the porosity of substrate,and reduce the substrate weight.With the increase of biochar,the effect is more obvious.20%of biochar treatment has the greatest influence on bulk density and pore size,and it can improve 10%and 9.3%respectively.2.After adding biochar,the temperature and moisture of the winter and summer two seasons can be significantly adjusted.Under the high temperature in summer,the biochar can reduce the temperature of the substrate and increase the moisture,but in winter it can increase the temperature and moisture in the substrate.However,when the solar radiation is strong and the temperature of the environment is too high in summer,20%of the biochar treatment was increase the temperature of the roof substrate,and the optimal temperature and water condition in summer were the biochar treatment of 10-15%.3.Adding biochar can effectively neutralize the pH value of roof soil,and the more the amount of application is,the more obvious the effect is.And as time goes on,the change of roof pH gradually slows down.5-20%biochar treatment reduced soil pH value by 6.1-12.7%.4.Biochar treatment can significantly improve soil nutrient content(C,N,P and K).10-15%biochar treatment were the best treatments to improve the effect.The total carbon content of substrate 25.2-58.7%,total nitrogen content of 27.5-1 15.2%,total phosphorus content of 6.3-28.2%and total potassium content of 7.0-35.7%could be improved by applying biochar.20%biochar treatment in summer has lower nutrient content than 10-15%biochar treatment,but winter is the highest.5.The application of biochar significantly increased the biomass of the soil microbes on the roof and improved the microbial community structure.In one year,the biochar treatment of 10-15%had the most obvious effect on the improvement of the roof microbes.Biochar can increase the total microbial biomass of 47.1-66.1%on the roof,and increase the biomass of 82.2%-101.4%fungi,38.1-62.5%actinomycetes,53.6-100.3%arbuscular mycorrhizal fungi,272.1-595.6%anaerobes,but with reducing the bacterial biomass of 14.0-15.7%.In different seasons,biochar can effectively maintain the stability of microbial community structure on the roof and reduce the impact of seasonal changes on microbial community structure.In winter and summer,biochar affects microbial communities with different mechanism.In summer,biochar mainly affects the diversity and richness of microbial community structure by improving the physical properties of roof substrate(porosity,temperature and moisture).In winter,biochar mainly affects the diversity and stability of soil microbial community structure by improving the chemical properties of roof substrate(nitrogen,phosphorus and potassium).6.Biochar promoted the growth of three plants(Ryegrass,Sedum lineare and Cucumber)with different environmental responses.5-10%biochar treatment had the best effect on ryegrass.Compared with no biochar treatment,it could increase the biomass by up to 171.4%;15-20%biochar treatment had the best effect on the Sedum lineare,compared with the treatment without biochar,it could increase the biomass by up to 163.3%;10-15%biochar treatment had the best effect on Cucumber,compared with no addition.Biochar treatment can increase up to 98.9%of biomass.In addition,the addition of biochar promoted plant photosynthesis and increased the carbon content of plants.Biochar increased the roof plant available water by 8.1-51.6%and delay of the days to reach permanent wilting point for up to 1.8 days,which plays an important role in the survival of plants in summer.In addition,biochar can also improve plant growth by increasing the content of substrate water and effective nutrients.7.Biochar addition can significantly reduce the rainfall and rain quality of roof runoff.For medium and small rain runoff can be reduced to more than 95%;in rainstorm,biochar can increase rainfall interception 17.8-72.3%.Biochar improves the interception of rainwater 10.1-22.9%with heavy rain.Biochar can effectively purify runoff quality and change pH value of roof runoff.Compared with cement roofs,biochar can reduce roof runoff pH value by 18.0-24.6%.At the same time,biochar can obviously reduce the suspended matter(TSS)of the roof runoff,which reduces the 12.6-30.6%TSS compared with the no biochar,and reduces the 28.5-43.2%TSS compared with the cement roof.Compared with cement roofs,all treatments of roof greening have better nitrification capacity,and biochar can enhance ammonia nitrogen in 8.8-1 1.1%of roof greening runoff.The retention effect of biochar on TP in roof runoff is higher than that in TN.Compared with no biochar treatment,the treatment with biochar can reduce 7.4-18.1%TP and 14.3-42.9%TN in roof greening runoff.The PO43--P removal rate of biochar treatment for roof runoff can reach more than 90%.Moreover,biochar can change the structure of nitrogen and phosphorus in runoff,so as keeping the nutrient elements in rainwater.8.Adding biochar to regulate the roof temperature and the near surface temperature of the roof.Results show that the highest surface temperature of the biochar substrates in summer is lower than that of the no biochar treatment,which is lower by 6.2-8.5%.While the highest temperature at the bottom of the biochar substrates in the daytime is lower by 9.3-15.0%than no biochar substrate,and the lowest temperature at the bottom of the night is reduced by 19.8-27.8%.In winter,the substrate temperature of biochar treatment is higher than that of without biochar treatment(5.1-31.3%).In addition,biochar can reduce the roof near surface temperature by 1-4? in different summer climates,thereby adjusting the building microclimate.The simulation results of Design Builder building model show that the addition of biochar can effectively improve the cooling effect of roof greening on the roof in summer.It also can reduce the thermal radiation range of the roof,and reduce the maximum indoor temperature of the top floor of the building about 1.5-4.8%and the building energy consumption of 0.82-1.38 kWh m-2 a month.9.Adding biochar can significantly improve the air quality of roof and reduce the concentration of particles.The experiment shows that biochar green roof can reduce the CO2 of 7.3-28.8%,CO of 10.6-20.7%,SO2 of 9.8-21.6%,NO2 of 2.1-11.5%.In addition,the results show that biochar can improve the adsorption of particles in the air and reduce the PM2.5 of 24.0-46.6%,PM1.0 of 3.7-23.3%,PM10 of 17.3-38.4%.The environment of high temperature is not conducive to the reduction of tiny particles like PM1.0.10.Based on the ecological economic model of 20 million m2 roof greening in Nanjing,the application of biochar can significantly increase roof ecological benefits,including rainfall interception,energy conservation and air purification.Compared with no biochar,biochar can improve the rainfall runoff by increasing the porosity of the substrate.Thus reducing the level and probability of urban flood and waterlogging,reducing the cost of urban rainwater management and treatment by about 27 million 290 thousand yuan per year.Biochar can reduce building energy consumption by improving the cooling effect of roof greening,and it can reduce energy consumption by?134 million 50 thousand yuan per year.Biochar can also effectively reduce air pollutants by promoting plant growth and improving the substrate properties.The cost of direct and indirect losses due to air quality problems can be saved by about 7 million 100 thousand yuan and 52 million 640 thousand yuan.Every year the ecological benefits with biochar application can increase the total of 41.3%,about 621 million 80 thousand yuan.And the application of biochar can increase 40 million yuan of solid waste recycling and increase the investment life of 1-3 years of roof greening.To sum up,according to this study,we can conclude that the application of biochar on the roof can adjust the ecological benefits of the roof from a variety of aspects(biological and abiotic),improving the overall environmental quality of the city,reduce the cost of urban pollution control.With the temperature,light of the roof environment and plants species,the limit of the application of biochar should be controlled in a reasonable range(the best effect of 10-15%biochar was applied in this study).Biochar as a green roof improver is not only feasible,but also can better enhance the ecological benefits of the roof. |
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