屋顶绿地碳固定潜力的研究

屋顶绿化因为能减轻城市内涝、热岛效应和空气污染等一系列城市化带来的负面影响,在很多国家和地区已经得到推广和应用。通过野外调查对10个用草坪草建植的简单式屋顶绿地的碳固定潜力进行评价,并探讨影响其碳固定能力的各种因子。同化箱试验的结果表明,屋顶绿地在白天可以通过吸收和固定CO2,降低其周围空气中的CO2含量。在多云清冷的上午,由朝鲜结缕草或狗牙根为主建植而成的屋顶植被在1 h内吸收的CO2可达0.46 g·m-2,在5 min内同化箱里CO2体积分数的降低幅度可达42%(162×10-6);地上部分碳储量试验的结果表明,以草坪草为主建成的屋顶绿地植被的地上部平均固定的有机碳为92.55 g/m2。故屋顶绿地是城市内小型碳库,具有一定的固碳作用。同时,基质厚度与草坪草地上部分的有机碳含量呈显著的正相关,也说明基质厚度可能是影响屋顶绿地碳固定潜力的重要因素。

Carbon Sequestration Potential of Extensive Green Roofs

Green roofs, an increasingly visible component of urban environments, are becoming increasingly popular in many countries and have attracted much attention in China. The interest for green roofs has been related to their benefit as the crucial determinants of energy flux and of buildings water retention, so as to reduce stormwater runoff volumes and peak flows, mitigate effect of urban heat island and also provide urban habitats to improve urban biodiversity. However, there is rare research focusing on its carbon sequestration potential and the mitigation of climate change. In present study, two experiments were conducted on 10 green roofs with the objective of evaluating carbon accumulation potential of green roofs and the factors that affect green roof carbon storage. In the chamber experiment, a green roof was able to absorb CO^₂ as high as 0.46 g per m² in one hour, and CO^₂ concentration declined as much as 162×10^-6 over 5 minutes. Mean decrease of CO^₂ concentration and CO^₂ exchange rate in the chamber over the measurement period were 77.8×10^-6 and-0.24 g·m^-2·h^-1, respectively. However, there was a high degree of variability because the photosynthesis rate of green roof plant greatly is dependent on light intensity and temperature, which change from time to time. Decrease of CO^₂ concentrations ranged from 23.50×10^-6 to 162.00×10^-6, and CO^₂ exchange rates ranged from-0.06 to-0.46 g·m^-2·h^-1 in the chamber. In the aboveground harvest experiment, data of the carbon reserve investigations showed that these green roofs stored an average of 92.55 g·m^-2in aboveground biomass with also a wide variability(from 39.47 to 138.41 g·m^-2), depended on the harvested biomass and carbon content of the biomass collected from the studied green roofs. In addition, it is notable that a significant correlation (R²=0.93) was observed between plant carbon content and substrate depth, while the correlations between substrate nutrient variables and carbon content was not statistically significant. Overall, the experimental results suggested that green roof can reduce the CO^₂ concentration in surrounding environment by absorbing CO^₂ in the daytime and act as a small carbon sink in urban area. It is likely that substrate depth may have big impacts on green roof carbon sequestration potential. Additional sophisticated research should be needed to evaluate the factors that contribute to the carbon sequestration potential of green roofs.