INTRODUCTION
Urban area
Urban land use affects some 1.0 x 10^6 km² of the earth’s surface, with ~57% of the human population currently residing in cities, that is about 1500 times the size of the city of Edmonton; this figure is ~82% in Canada (World Bank, 2022). A doubling in global urban land use is projected by 2100 (Gao and O’Neill, 2020). Urban areas are hotspots for greenhouse gas (GHG) emissions, accounting for more than half of estimated emissions globally (Crippa et al., 2021). Energy use of the built environment and transportation sectors generally dominates emissions; however, GHG emissions from urban soil and waste streams are large but poorly resolved contributors. Recent satellite observations specifically indicate large methane (CH4) emissions from urban areas (Plant et al., 2022). CH4 is second to CO2 in importance as a GHG, accounting for ~30% of net anthropogenic climate forcing (Saunois et al., 2020). Targeting reductions in CH4 emissions to meet greenhouse gas targets is an attractive policy option relative to CO2 (Crill and Thornton, 2017; Nisbet et al., 2020). The short half-life of CH4 in the atmosphere implies that reductions in net emissions can have large impacts on climate forcing over a much shorter timeframe (Saunois et al., 2020; Crill and Thornton, 2017; Nisbet et al., 2020).
(Crippa et al., 2021)
https://doi.org/10.1088/1748-9326/ac00e2
Biochar
Biochar – defined as pyrolyzed biomass used as a soil amendment (Lehmann and Joseph, 2015) – is an important emerging technology of importance to GHG emissions mitigation (Li et al., 2018). Biochar has gained recent attention as one of only a handful of existing “negative emissions” technologies that can remove CO2 from the atmosphere at scale (Smith, 2016; Werner et al., 2022), and as a versatile material for increasing efficacy of the circular economy (Singh et al., 2022). Biochar utilization has the potential to further reduce GHG emissions from urban soil and to enhance C uptake and other environmental services from urban forests and green infrastructure. Unlike other forms of organic matter, biochar is highly recalcitrant (Spokas, 2010), implying that biochar added to soils results in long-term C sequestration. Recent syntheses suggest that large-scale implementation of biochar systems could offset 3.4-6.3 Pg CO2e, or ~10-15% of global GHG emissions (Lehmann et al., 2021); however, considerable uncertainty persists on long-term effects on plant growth and soil processes. Biochar acts as a liming agent and reduces the bioavailability of most toxic metals (Beesley et al., 2010; Rees et al., 2014), and salts (Thomas et al., 2013), particularly important issues in urban environments. Biochar also increases soil cation exchange and water-holding capacity, reduces soil bulk density (Atkinson et al., 2010; Joseph et al., 2021), and provides a direct source of nutrients to plants, including Potassium (K), Phosphorus (P), Calcium (Ca), Magnesium (Mg), and Boron (B) (Gezahegn et al., 2019). A meta-analysis of tree growth responses to biochar found an average 41% increase in biomass (Thomas and Gale, 2015). Although urban forestry studies on biochar are few, large increases in tree growth on urban soils have also been found (Scharenbroch et al., 2013; Somerville et al., 2020), particularly when biochar additions are combined with additional sources of nitrogen, such as N-fixing companion plants (Sifton et al., 2022).
(He et al., 2017)
https://doi.org/10.1111/gcbb.12376
An additional potential benefit of biochar use in urban ecosystems is the potential to mitigate substrate GHG emissions, in particular of CH4. In agricultural soils biochar consistently reduces nitrous oxide (N2O) emissions (He et al., 2017); however, biochar also can strongly reduce CO2 and CH4 emissions in either compacted or periodically flooded soils (Jeffery et al., 2016). Urban forests and green infrastructure can potentially serve as a sink for GHGs. For example, different substrate and vegetation types on green roofs can result in these systems being either a source or sink for GHG (Halim et al., 2022; Teemusk et al., 2019). Green infrastructure can also potentially modify energy demand; for example, urban forests generally attenuate wind and mitigate urban heat island effects (Livesley et al., 2016; Ziter et al., 2019), and enhanced growth and physiological status of trees would be expected to enhance this effect.
(Peng et al., 2023)
https://doi.org/10.3390/su15064861
The proposed project will quantify direct GHG emissions from urban forestry and urban soils, and will explore novel soil amendment and vegetation planting strategies to reduce these emissions, and enhance overall C sequestration, with a focus on biochar as an urban soil amendment.
Objectives
01
Assess the potential to mitigate GHG emissions by processing urban forestry waste to produce biochar and to utilize this biochar in urban forestry and other forms of urban green infrastructure.
02
Evaluation of responses of tree growth and physiological performance to substrate amendments with biochar and biochar-derived products.
03
Explore the effect of biochar application on various soil properties, including soil pH, nutrient availability, microbial biomass, and organic carbon content.
