Investigating Variability in CO2 Fluxes in Urban Gardens, Oakland CA

Abstract

One of the many strategies used to advance climate mitigation research involves investigating variability in biogenic CO₂ in the urban environment. A limited number of studies have focused on urban residential gardens and their contributions to the carbon cycle. This study used the closed chamber method to capture a snapshot in both time and space of the variability of CO₂ and H₂O fluxes from two residential front gardens in Oakland Ca. The fluxes of CO₂ from two lawns, a common perennial grass, Lomandra longifolia, and decorative bark were measured to determine Net Ecosystem Exchange (NEE) of the various ground covers. Our results show that the NEE at both lawns proved to be strong carbon sinks, during peak photosynthesis, however differed significantly in magnitude. Meanwhile, our bark and L. longifolia samples proved to be small sources of CO₂ and similar in magnitude. Further, we were able to determine the Gross Primary Productivity (GPP) and ecosystem respiration (R_eco) at each vegetated sample plot, where results show lawn plots, due to a much higher percentage of canopy cover, have a much greater GPP than L. longifolia. However, R_eco from lawns measured approximately twice as much CO₂ than our L. longifolia or bark plots. Furthermore, we estimated the autotrophic respiration (R_auto) from L. longifolia, where R_auto rates were very small, likely due to L. longifolia only taking up a small portion of chamber footprint area. Observed GPP was further used to estimate the carbon sequestration capacities of each type of vegetation by scaling up Fractional Green Canopy Cover (FGCC). Our estimates show that L. longifolia, at 100 percent FGCC had estimated carbon sequestration capacities similar to those of our lawn samples. Using this information, along with comparing the soil moisture and evapotranspiration rates between vegetated plots we determined L. longifolia to be a good plant choice for reducing CO₂ emissions gardens while using less water than required for lawns.