Soil organic carbon storage changes in Yangtze Delta region, China

Soil carbon sequestration plays an essential role in mitigating CO₂ increases and the global greenhouse effect. This paper calculates soil organic carbon (SOC) storage changes during the course of industrialization and urbanization in Yangtze Delta region, China, based on the data of the second national soil survey (1982–1985) and the regional geochemical survey (2002–2005), with the help of remote sensing images acquired in periods of 1980, 2000, 2005. The results show that soils in the top 0–20 and 0–100 cm depth in this region demonstrate the carbon sink effect from the early 1980s to the early 2000s. The SOC storage in 0–20 cm depth has resulted in increase from 213.70 to 238.65 Tg, which corresponds to the SOC density increase from 2.94 ± 1.08 to 3.28 ± 0.92 kg m⁻², and mean carbon sequestration storage and rate are 1.25 Tg a⁻¹, 17.14 g m⁻² a⁻¹, respectively. The SOC storage in 0–100 cm depth has resulted in increase from 690.26 to 792.65 Tg, which corresponds to the SOC density increase from 9.48 ± 4.22 to 10.89 ± 3.42 kg m⁻², and mean carbon sequestration storage and rate are 5.12 Tg a⁻¹, 70.32 g m⁻² a⁻¹, respectively. Urban area in Yangtze Delta region, China, increased more than 3,000 km² and the urban growth patterns circled the central city region in the past 20 years. The SOC densities in 0–20 cm depth decrease gradually along urban–suburban–countryside and the urban topsoil is slightly enriched with SOC. Compared to the data of the second national soil survey in the early 1980s, the mean SOC density in urban area increased by 0.76 kg m², or up 25.85% in the past 20 years. With the characteristics of SOC storage changes offered, land-use changes, farming system transition and ecological city construction are mainly attributed to SOC storage increases. Because of lower SOC content in this region, it is assumed that the carbon sink effect will go on in the future through improved soil management.