Carbon Sequestration in Urban Soils for Enhancing the Resilience of Urban Ecosystems to Climate Change.

Urban ecosystems occupy 0.5% of the Earth’s total land area. However, the urban land area is expanding with annual urban land expansion growth rates of 7.5% in China, 4.8% in India, 4.3% in Africa, 3.3% in North America and 2.5% in Europe. This global-scale urbanization causes carbon (C) losses from the biosphere. Properly managed urban soils can mitigate some of the losses by retaining C from the atmosphere as stabilized soil organic carbon (SOC) such as mineral-associated organic matter (OM) or black carbon (BC) and as stabilized soil inorganic carbon (SIC) such as stable secondary carbonates. SOC stocks of up to 810 Mg C ha-1 to 1.5-m depth (Serebryanye Prudy, Russia) and SIC stocks of up to 300 Mg C ha-1 to 2.5-m depth (Newcastle upon Tyne, U.K.) have been reported. However, the data on rates of soil C sequestration and sink capacity are scanty. Aside contributing to climate change mitigation, protection and increasing urban SOC stocks support critically important soil-derived ecosystem services, including water filtration, erosion control, soil strength and stability, nutrient conservation and cycling, and pollutant immobilization. Thus, soil C storage and the C capture functions of urban soils within the constructed environment should be considered when planning for new or existing developments. Further, C-friendly soil and land-use management practices must be implemented to enhance (i) soil-derived ecosystem services in urban areas and (ii) the resilience of urban ecosystems to climate change.