Carbon stocks and CO2 emissions of urban and natural soils in Central Chernozemic region of Russia

- SOC stocks in urban soils depended on the functional zoning and background natural soils.
- Urban SOC stocks in 1.5 m depth ranged 20 to 50 kg C m− 2 which was 20% less than in reference natural soils.
- Urban soils had greater subsoil (below 50 cm) SOC stocks than natural.
- The CO2/SOC stock ratio was two-three times higher in urban soils compared to natural.
- Urbanization can decrease sustainability of SOC stocks in the regions, dominated by Chernozems.

C-sequestration, as a function of soils, is known to help mitigate climate change. However, the potential of urban soils to be C-sinks or sources, is widely unknown. This study aims to understand the role and significance of urban soils in the C-balance of the region. It reveals several important findings about the C-balance capacities of urban soils and the multiple factors affecting this balance. This two-year study focused on soil organic carbon (SOC) stocks and CO2 emissions of urban soils in the city of Kursk, located in the Central Chernozemic region of Russia, an area known to have some of the most fertile soils in the world. SOС stocks and emissions were studied in residential, recreational, and industrial functional zones and in comparison to corresponding natural reference soils to analyze the influence of urbanization on C turnover Urban soils were found to store 20 to 50 kg С m− 2 in 1.5 m layer; 10-30% less than in corresponding natural Luvic Chernozems and Chernic Phaeozems, but greater than what has been reported for many other cities. The urban soils with developed cultural layers stored more C in subsoil compared to the natural soils. Emissions of CO2 in urban soils, however, were higher than from Chernic Phaeozems but comparable to those from Luvic Chernozems. The CO2/SOC stocks ratio in urban soils was two-three times higher than in natural soils. These outcomes point to the intensive C turnover and low sustainability of SOC stocks in urban soils. This study found evidence that the recent urbanization of the Chernozemic region has adversely affected the C balance. Natural soils in the region are important C sinks, however they can convert to C sources in result of urbanization.