Global soil organic carbon stocks in natural and urban ecosystems
Shih-Chieh Chien
PhD Student, Montclair State University, USA
Figure 1 Soils in natural (left), urban green space (middle) and urban intensive (right) habitats. From left to right, pictures are taken in Harriman State Park, NY, USA; Central Park, NY, USA; Jersey City, NJ, USA (Photo credit: Shih-Chieh Chien).
Despite efforts to mitigate climate change, it still remains challenging for humans to reduce carbon emissions and meet carbon neutrality under the pressure of increasing global population and urbanization.
In terrestrial environments, soil is the largest organic carbon sink and offers the greatest opportunity to mitigate the global carbon imbalance. Soil organic carbon (SOC) stocks originate from detritus and root exudates. When stable, these compounds can store the carbon that plants absorb from the atmosphere. However, the capacity for soil to store carbon is determined by a variety of parameters associated with different climatic zones and vegetation biomes. The interactions of these parameters can be difficult to predict, especially in urban environments where limited data on carbon storage have been synthesized.
In this study, we conducted a meta-analysis by collecting SOC data from published literature. We defined each study location as a natural, urban green space, or urban intensive habitat (Fig. 1) and compared those carbon stocks within defined climatic zones, vegetation types, and the Human Footprint (a unitless metric reflecting the extent of human disturbance) in each study location. Our analysis revealed that SOC stocks are higher in natural than in urban habitats, and we found a negative relationship between SOC and the human footprint only in natural habitats. The highest SOC and greatest variation in natural habitats reflect the varied environmental conditions and vegetation types which characterize the way natural soils store carbon. Critically, these factors are less influential in urban environments where anthropogenic influences dominate. Urban ecosystems tend to be uniform as they are defined by human living constraints, decreasing SOC variability over increasing Human Footprint values.
Our work helps present a globally comprehensive picture of SOC stocks between natural and urban ecosystems, provides a useful reference for future natural resource management and urban design and highlights the importance of urban SOC storage to managing global soil carbon budgets.
Publication: Chien, S. C., Krumins, J. A. (2022). Natural versus urban global soil organic carbon stocks: A meta-analysis. Science of The Total Environment, 807, 150999. DOI: https://doi.org/10.1016/j.scitotenv.2021.150999