Beyond Total C: Integrative Analysis of Carbon Forms in Urban Soils

Abstract

The precise differentiation and quantification of ecosystem-driven organic carbon (OC_eco), black carbon (BC), and inorganic carbon (IC) in soil is essential for understanding the global carbon cycle. However, the absence of a standardised method for differentiating among these carbon types is a notable challenge in soil carbon research. We addressed this gap by establishing CO₂-evolved gas analysis (EGA) with peak deconvolution, a robust approach to parse OC_eco, BC, and IC in soils through CO₂ thermograms derived from ramped combustion. The soils in urban greenery were used for developing this methodology due to their exposure to various carbon sources. Our method's precision was confirmed using model mixtures, exhibiting high accuracy (R² > 0.90) with regression lines approximating the ideal 1:1 line of known versus measured values. Applying this technique, we identified distinct spatial distributions of OC_eco and BC. Their distributions were strongly influenced by the balance between green spaces and impervious surfaces in surrounding land uses. Conversely, IC appears unaffected by such land use dynamics. Our results provide compelling evidence that without a distinct recognition of BC and IC from OC_eco, assessments of urban carbon storage are prone to significant overestimation. Because urban soil C types differ in source and dynamics, our findings call for a recalibration of urban soil carbon accounting frameworks to prevent overestimations of vulnerability or sequestration potential, which is critical for effective climate mitigation strategies and policy planning. In essence, our findings underscore the necessity of advanced soil analysis techniques in urban soil management and provide a valuable tool for future research in urban ecosystem dynamics.