Abstract
Abstract. Urban surfaces are usually net sources of CO2. Vegetation can potentially have an important role in reducing the CO2 emitted by anthropogenic activities in cities, particularly when vegetation is extensive and/or evergreen. A direct and accurate estimation of carbon uptake by urban vegetation is difficult due to the particular characteristics of the urban ecosystem and high variability in tree distribution and species. Here, we investigate the role of urban vegetation in the CO2 flux from a residential neighbourhood in Singapore using two different approaches. CO2 fluxes measured directly by eddy covariance are compared with emissions estimated from emissions factors and activity data. The latter includes contributions from vehicular traffic, household combustion, soil respiration and human breathing. The difference between estimated emissions and measured fluxes should approximate the flux associated with the aboveground vegetation. In addition, a tree survey was conducted to estimate the annual CO2 sequestration using allometric equations and an alternative model of the metabolic theory of ecology for tropical forests. Palm trees, banana plants and turfgrass were also included in the survey with their annual CO2 uptake obtained from published growth rates. Both approaches agree within 2% and suggest that vegetation sequesters 8% of the total emitted CO2 in the residential neighbourhood studied. An uptake of 1.4 ton km−2 day−1 (510 ton km−2 yr−1) was estimated as the difference between assimilation by photosynthesis minus the aboveground biomass respiration during daytime (4.0 ton km−2 day−1) and release by plant respiration at night (2.6 ton km−2 day−1). However, when soil respiration is added to the daily aboveground flux, the biogenic component becomes a net source amounting to 4% of the total CO2 flux and represents the total contribution of urban vegetation to the carbon flux to the atmosphere.
Highlights
Effective mitigation of greenhouse gases (GHG) must be based on a good understanding of all emission sources and sinks
To investigate whether tropical urban vegetation sequesters more CO2, the present study investigates the influence of urban vegetation on the CO2 flux from a residential neighbourhood in Singapore.We use two independent approaches to quantify the direct removal of CO2 from the atmosphere by vegetation
The CO2 assimilated during daytime and released by dark respiration lead to different diurnal patterns in the observed CO2 flux by eddy covariance (EC) and the sum of emissions estimated by bottom-up approaches
Summary
Effective mitigation of greenhouse gases (GHG) must be based on a good understanding of all emission sources and sinks. Carbon dioxide (CO2), the GHG with the most important global warming potential on a 100 yr timescale, is emitted by burning of fossil and biomass fuel associated with transport, energy use in households and public buildings, as well as by manufacturing and industry in urban centres. Contribute to the total CO2 emissions from cities, but do not always occur within urban boundaries. The net urban CO2 flux is further influenced by natural sources and sinks. The metabolic release of CO2 by human respiration is an important and growing component that cannot be neglected in densely populated cities (Prairie and Duarte, 2007)
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