| Since plants in urban green space is photo synthetic and the soil can accumulate organic carbon the urban green space is generally considered as a carbon sink, but the green space itself, in its full life cycle process will also produce carbon emissions. Mechanicals used in the construction and maintenance processes emit carbon though burning of fossil fuels, the use of materials such as water, inorganic fertilizers and pesticides also produce a certain amount of carbon emissions in the production, packaging and transportation phase. This increases the difficulty of quantifying urban green space as carbon sinks.Carbon footprint model is a potential tool for us to quantify and evaluate carbon sequestration and carbon emissions of the urban green space in its life cycle, but as so far researchs for carbon footprint of urban green space are still rare. The study is the first establisment to account for and evaluate the carbon footprint in Guangzhou typical urban green space in order to provide a basis for related research and reference.In this study, we selected seven typical urban green spaces as our study areas. We calculated the aboveground and belowground biomass of the trees and the sPubs which are higher than1meter in the seven study areas, then converted them to the carbon storage density which is between0.66-11.22kgC/m2.Soil organic carbon density of the seven study areas is between1.65-8.35kgC/m2.We get this result by measuring the density of organic carbon of the soil samples of all the study areas. We calculated carbon emissions which are between0.63-1.78kgC/m2and0.01-0.71kgC/m2·a respectively in construction and maintenance phases by investigating the staff of the related department and data collection.We established the carbon footprint model on the basis of the above results. The carbon footprint model can be briefly described that the green carbon footprint equals to the total carbon emissions in the full life cycle of the green space subtracting the total amount of carbon sequestration, if the value is negative, the total carbon emissions is less than the total amount of carbon; Inversely, if the value is positive, the total carbon emissions are greater than the total amount of carbon sequestration. And we have verified the the carbon footprint model green by calculating the carbon footprint of the seven study areas which are between-2.63-1.99kgC/m2.The carbon footprint of yueJiangdong Road (R1) and DunFeng Road garden Lawn (P3) are1.99kgC/m2and0.59kgC/m2,respectively. If the lifetime of the green spaces were assumed to be30years the two study areas’carbon footprints would be17.04kgC/m2and-4.45kgC/m2. This shows that urban green space in its full life cycle is not necessarily a net carbon sink, contrarily it may be a net carbon source. The study also prodicts the total carbon footprint of all the urban green spaces in Guangzhou (supposing a30-year life cycle) is about-7.05×106t, accounting half for the carbon sequestration by the plants and soil, the other half is offset by maintenance carbon emission.We tried to give three kinds of scenarios by changing the plant design, measures of construction and maintenance founding that for road green, irrigation is the greatest contribution to carbon emissions to the total carbon emission; For the parks, water-saving irrigation substituting for traditional irrigation is also a great idea. Both for the two kinds of green spaces, a reasonable choice of plants which have greater carbon sequestration rates can play a very large role in carbon sequestration and reduction of carbon footprint.The study also proposed low-carbon design guidelines and maintenance approach to increase the carbon sink and to reduce the carbon emissions of the urban green spaces in order to provide a reference for future research. |
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