Major controls on soil respiration (R_s), including soil moisture (θ), soil organic carbon (SOC), and soil temperature (T_s) are manipulated in management of urban vegetation such as residential lawns. Irrigation, fertilization and elevated nocturnal temperatures due to the urban heat island effect are expected to show an increase in soil respiration rates. One of the few studies that measured SOC after urbanization (Golubiewski, 2006) showed that urban management increased SOC in the long-term after an initial decrease. Koerner and Klopatek (2002) used a closed-chamber technique to measure soil respiration in rural and quasi-urban lots (golf courses) in Phoenix, AZ and concluded that soils with high irrigation and intensive management showed up to ten times higher soil respiration rates compared to the native soils in the city's hinterland. However no systematic data is currently available to specifically explore the impacts of irrigation and green-space management on soil respiration.

The objective of this research was to find out how R_s in highly managed urban vegetation responds to various irrigation and fertilization regimes and to determine whether specific management strategies can influence urban carbon exchange. Quantifying the magnitude of soil respiration in urban vegetation will also help in partitioning CO₂ emissions between combustion processes and biogenic sources in suburban areas.

We made periodic measurements of R_s using a portable system equipped with an opaque PVC chamber, on eight lawns in two residential neighborhoods in Vancouver, BC, Canada. T_s at the 5 cm depth and θ in the 0-10 cm layer were also simultaneously measured using a copper-constantan thermocouple and a hand-held TDR probe, respectively. All sites were within the footprints of eddy covariance (EC) systems monitoring CO₂ exchange at the local-scale (Crawford et al., 2009). Additionally, respiration and climatic conditions at two unmanaged (i.e. non-irrigated and non-fertilized) grassland sites in the region were measured as a reference. During summer 2008, measurements made prior to, during, and after scheduled periods of irrigation provided a range of soil moisture and soil temperature conditions. Based on correlations between Rs and T_s and θ, we developed an empirical model of urban soil respiration and discuss the impact of irrigation and green-space management on the urban carbon cycle.

References

Crawford B. et al., 2009, same conference.

Golubiewski N.E., 2006, Ecological Applications, 16, 555-571.

Koerner B., Klopatek J., 2002, Environ Pollut., 116, S45-S51.