The impact of urbanization on soil organic carbon stocks and particle size and density fractions

International audience; PurposeUrbanization is a major driver of land use change and can affect the soil organic carbon (SOC) pools. This study aimed to understand the urbanization impact on SOC stocks and pools at profile scale (0–100 cm).MethodsThe SOC was studied at 0–30 and 0–100 cm depths in park and sealed soils of three French cities (Marseille, Nancy, and Nantes). Physical fractionation was performed to gain insight on the size of different SOC pools (particulate and organo-mineral soil fractions).ResultsThe SOC stocks were seven to ten times higher in parks than in sealed soils, but lower than in natural soils according to literature data. The contribution of the first 30 cm to profile SOC stock was around 40%, with strong heterogeneity, especially in sealed soils. Considering the whole 0–100 cm profile, SOC stocks in particulate organic matter fractions (light fraction > 50 µm) were 25–48 times higher in parks than in sealed soils, while SOC stocks in mineral-associated fractions ( 50 µm, particularly in sealed soils (11% in average at 0–100 cm depth). This fraction associated to sand is usually poor in SOC in natural or agricultural soils. In these urban soils, it might be bitumen, a dense organic artifact.ConclusionThe SOC stocks up to 100 cm depth and their heterogeneity pleaded to strengthen and expand SOC studies in all urban soils.