| Chengdu City government, combining both condition of Chengdu Plain and local city development, timely declared to develop a modern garden city (MGC) which it will be very harmonious with human being and nature,urban and rural areas. And construction of green roofs is one of contents in the development of Chengdu MGC. To date, although the positive effects of green roofs on developing low carbon society from green roofs with a great ecological benefits and economic benefits have been widely accepted by the public, the basic data are still too limited to widely apply and scale upthe green roofs, so that it became a barrier on the processes of Chengdu MGC. Therefore, four main contents of this study are follows:(1) the discussion of green roof designation; (2) the discussion of green roof plants and substrates selection and configuration in MGC; (3) the analysis of green roof Carbon sequestration, including carbon sequestration of plants and substrates; and (4) the analysis of energy saving and CO2 emission reduction of green roofs. Main results are as follows:1. Three different substrates (waste-building-materialsubstrate (WBMS, particles size <3mm), and mixed sewage-sludge substrate (MSSS, volume ratio of sewage sludgeand local natural soil is 1:1) andlocal-nature soil (LNS) and three types of native plants (Ligustrum vicaryi, Nephrolepis auriculata, Liriope spicata) were selected to have an one-year comparative experiment study. The results show that:(1)the three types of substrates were in a middle level with relatively high TOC (Total Organic Carbon)contents, but it was not obvious that TOC contents of substrates decreased with the increasing substrate depth because of limited substrate depth.The fixed carbon dioxide (CO2) content of MSSS and LNS was higher than WBMS. (2) MSSS and LNS were good ability of carbon sequestration. (3) MSSS was the best substrate for plant growth because of its high nutrition and water content. (4) There was little different TOC contentsamong the three plants, but carbon sequestration was the following order:Ligustrum vicaryi (2.75kg/m2·yr) > Liriope spicata(0.997kg/m2·yr)>Nephrolepis auriculata(0.97kg/m2·yr). Moreover, Ligustrum vicaryi grew better and had the highest CO2 fixation, while the growth of Nephrolepis auriculata and Liriope spicata was not good, because they had weak ability of drought-enduring and cold resistance. (5) Carbon sequestration of the whole green roof system in this study was 4.7kg/m2·yr, equivalently 190.5kg/yr carbon dioxide. Since green roofs plants and substrates had better carbon sequestration ability, green roof was a great carbon sequestration system.2. Other results are below:(1) green roofs by reasonably designed and built, could meet the requirements of safe and reliable, low carbon and environmental protection, and beautiful landscapes. (2) By comparing the temperature changesin each monitoring point, it could be found that green roofs had good effect of cooling in summer (1.2℃)and heat preservation in winter (2.5℃). Comparing with a 1.5P air conditioner, energy saving by green roof would be 111kw·h per year. (3) Meanwhile, Green roofs could reduce CO2 emission 17.25 kg/m2·yr by green roof plants and substrates. (4) It was about 1.64×108kg/yrCO2 emission in Chengdu MGC according to the calculation conditions(a.50% of Chengdu roof area(38km2) would be afforested; b. greening ratio was 50%; c. substrates configuration were WBMS, LNS and MSSS with the depth of 25cm from this study; d. plants configuration of Ligustrum vicaryi, Nephrolepis auriculata, Liriope spicata was 1:1:1). (5) At the same time, the benefit of CO2 reduction was closely related with substrate type and depth, plant type, climate conditions. Besides, the study area of green roofs was an ideal carbon sink system. (6) Based on the same calculation conditions, Total carbon sink content was 190.5 kg C/yr in study area, and carbon sequestration in Chengdu MGC was about 4.47×108 kg C/yr. Therefore, it was obvious that green roofs had well environmental benefits and economic benefits.3. In conclusion, to build green roofs, the structural characteristics and circumstance conditionsof buildings should be carefully considered and the design must be reasonable. Meanwhile, suitable substrate and plant should be selected. Then the green roof can fullly play its environmental benefits and economic benefits. The results in this studywill make contributions to the construction of green roof in Chengdu modern garden city. |
PDF Full Text Request