Rapid urbanization through cropland encroachment in the Jiangsu-Zhejiang-Shanghai region of China leads to substantial soil organic carbon loss

Abstract Soil organic carbon (SOC) is a major terrestrial carbon reservoir, crucial for the global carbon cycle and climate change. However, the impact of urbanization-induced cropland encroachment on SOC remains underexplored. This study quantified SOC loss in the top 20 cm (SOC 20 ) and 100 cm (SOC 100 ) soil layers in the Jiangsu-Zhejiang-Shanghai (JZH) region from 1985 to 2019 using high-resolution land cover dataset and multi-temporal SOC maps. Our results show that the cumulative cropland encroachment area in the study area reached 18 925.65 km 2 , approximately three times the area of Shanghai. The encroached areas of cropland in Jiangsu, Zhejiang, and Shanghai accounted for 59.72%, 31.49%, and 8.79% of the total, respectively. The cumulative SOC 100 loss in the JZH region was approximately 65.31 ± 32.45 Tg C, with the SOC 20 loss contributing about 32.97%, emphasizing the importance of deep SOC pool. The cumulative SOC 20 (SOC 100 ) losses in Jiangsu, Zhejiang, and Shanghai contributed approximately 55.36% (57.74%), 35.76% (31.96%), and 8.87% (10.3%) to the total losses in the JZH region, respectively. Moreover, the annual average SOC 100 loss accounted for about 8.6% to 25.59% of the terrestrial carbon sink flux (11.24 Tg C yr −1 ) in the JZH region, emphasizing that SOC loss due to cropland encroachment cannot be overlooked when evaluating the regional carbon sink capacity. Additionally, the positive correlation between SOC loss and regional gross domestic product highlights the trade-off between economic development model of urban expansion through cropland encroachment and the resulting substantial SOC loss. This study emphasizes the importance of assessing the impacts of urbanization on regional SOC stocks, especially with regard to deep soil, and provides scientific insights for future urban planning and land management in this region.