School of Earth and Space Exploration, Arizona State University, Tempe, AZ, United States of America.
Departamento de Ingeniería Civil y Ambiental, Instituto de Ingeniería y Tecnología, Universidad Autónoma de Ciudad Juárez, Ciudad Juárez, México.
PLoS One. 2020 Feb 12;15(2):e0228537. doi: 10.1371/journal.pone.0228537. eCollection 2020.
Urbanization modifies land surface characteristics with consequent impacts on local energy, water, and carbon dioxide (CO2) fluxes. Despite the disproportionate impact of cities on CO2 emissions, few studies have directly quantified CO2 conditions for different urban land cover patches, in particular for arid and semiarid regions. Here, we present a comparison of eddy covariance measurements of CO2 fluxes (FC) and CO2 concentrations ([CO2]) in four distinct urban patches in Phoenix, Arizona: a xeric landscaping, a parking lot, a mesic landscaping, and a suburban neighborhood. Analyses of diurnal, daily, and seasonal variations of FC and [CO2] were related to vegetation activity, vehicular traffic counts, and precipitation events to quantify differences among sites in relation to their urban land cover characteristics. We found that the mesic landscaping with irrigated turf grass was primarily controlled by plant photosynthetic activity, while the parking lot in close proximity to roads mainly exhibited the signature of vehicular emissions. The other two sites that had mixtures of irrigated vegetation and urban surfaces displayed an intermediate behavior in terms of CO2 fluxes. Precipitation events only impacted FC in urban patches without outdoor water use, indicating that urban irrigation decouples CO2 fluxes from the effects of infrequent storms in an arid climate. These findings suggest that the proportion of irrigated vegetation and urban surfaces fractions within urban patches could be used to scale up CO2 fluxes to a broader city footprint.
城市化改变了地表特征，从而对当地的能量、水和二氧化碳（CO2）通量产生影响。尽管城市对 CO2 排放的影响不成比例，但很少有研究直接量化不同城市土地覆盖斑块的 CO2 状况，特别是在干旱和半干旱地区。在这里，我们比较了亚利桑那州凤凰城四个不同城市斑块的涡度协方差测量的 CO2 通量（FC）和 CO2 浓度([CO2])：干旱景观、停车场、湿润景观和郊区社区。分析 FC 和[CO2]的日变化、日变化和季节变化与植被活动、车辆交通计数和降水事件有关，以量化各站点与其城市土地覆盖特征相关的差异。我们发现，灌溉草坪的湿润景观主要受植物光合作用活动的控制，而靠近道路的停车场主要表现出车辆排放的特征。另外两个具有灌溉植被和城市表面混合物的站点在 CO2 通量方面表现出中间行为。降水事件仅对没有户外用水的城市斑块中的 FC 产生影响，表明城市灌溉将 CO2 通量与干旱气候中罕见风暴的影响解耦。这些发现表明，城市斑块内灌溉植被和城市表面部分的比例可用于将 CO2 通量扩展到更广泛的城市足迹。
