Soil respiration contributes substantially to urban carbon fluxes in the greater Boston area

Abstract

Urban areas are the dominant source of U.S. fossil fuel carbon dioxide (FFCO2) emissions. In the absence of binding international treaties or decisive U.S. federal policy for greenhouse gas regulation, cities have also become leaders in greenhouse gas reduction efforts through climate action plans. These plans focus on anthropogenic carbon flows only, however, ignoring a potentially substantial contribution to atmospheric carbon dioxide (CO2) concentrations from biological respiration. Our aim was to measure the contribution of CO2 efflux from soil respiration to atmospheric CO2 fluxes using an automated CO2 efflux system and to use these measurements to model urban soil CO2 efflux across an urban area. We find that growing season soil respiration is dramatically enhanced in urban areas and represents levels of CO2 efflux of up to 72% of FFCO2 within greater Boston's residential areas, and that soils in urban forests, lawns, and landscaped cover types emit 2.62 ± 0.15, 4.49 ± 0.14, and 6.73 ± 0.26 μmolCO2 m(-2) s(-1), respectively, during the growing season. These rates represent up to 2.2 times greater soil respiration than rates found in nearby rural ecosystems in central Massachusetts (MA), a potential consequence of imported carbon amendments, such as mulch, within a general regime of landowner management. As the scientific community moves rapidly towards monitoring, reporting, and verification of CO2 emissions using ground based approaches and remotely-sensed observations to measure CO2 concentrations, our results show that measurement and modeling of biogenic urban CO2 fluxes will be a critical component for verification of urban climate action plans.

Soil Media CO2 and N2O Fluxes Dynamics from Sand-Based Roadside Bioretention Systems

“…The average fluxes of CO 2 -C and N 2 O-N in this study are lower than average fluxes measured from fertilized urban lawns and turf and mulched garden beds [67,68], but greater than in native grasslands and wheat fields that received no irrigation and fertilization ( [69]; Figure 5). Average CO 2 -C fluxes observed in this study are lower than fluxes reported by Decina [56] from urban lawn and landscaped sites, but greater than average fluxes from urban [56] and rural forests [70] (Figure 5). For N 2 O-N, our average and range of fluxes were much smaller than the range of fluxes (30 to 900 µg m −2 h −1 ) observed from fertilized corn fields ([71]; Figure 5).…”

“…For both gases, temperature was positively correlated with gas fluxes. Various other environmental factors besides soil temperature and water content, and NH 4 + -N and NO 3 − -N concentrations regulate gas fluxes such as the amount of OM, mineralizable carbon, and microbial biomass [55][56][57], which are relevant to various stormwater control structures. Decina [56] observed significant and positive correlation of soil CO 2 efflux with soil organic matter concentration, soil C:N ratio and the depth of the leaf litter layer.…”

“…Various other environmental factors besides soil temperature and water content, and NH 4 + -N and NO 3 − -N concentrations regulate gas fluxes such as the amount of OM, mineralizable carbon, and microbial biomass [55][56][57], which are relevant to various stormwater control structures. Decina [56] observed significant and positive correlation of soil CO 2 efflux with soil organic matter concentration, soil C:N ratio and the depth of the leaf litter layer. Bettez and Groffman [55], who measured denitrification rates (1.2 mg N kg −1 h −1 ) from stormwater control measures (wet ponds, dry detention ponds, dry extended detention, infiltration basin, filtering practices), observed that the rates strongly correlated with soil moisture, OM, microbial biomass, and soil CO 2 efflux across sites.…”

Reconciling the differences between a bottom-up and inverse-estimated FFCO2 emissions estimate in a large US urban area

“…The research community is aware of the potential for soil/vegetation respiration outside the growing season to contribute to observed CO 2 mixing ratios, but empirical evidence in the urban domain has been limited. Only recently have there been measurements within mid-latitude urban areas to support the notion that the flux may be large enough to warrant explicit inclusion (Decina et al, 2016;Kaye et al, 2005;Chen et al, 2014). Indeed, the soil/vegetation covered landscape within the urban domain tends to be heavily managed with both water and soil nutrients available throughout the year (Kaye et al, 2006).…”

“…We draw from three studies that measured urban respiration fluxes in U.S. cities at times of the year coincident with the September-April period of the INFLUX inversion (Decina et al, 2016;Kaye et al, 2005;Chen et al, 2014). The three studies performed measurements in Boston MA, Fort Collins CO, and Baltimore MD.…”