Unveiling the Spatiotemporal Evolution and Driving Mechanisms of Ecosystem Carbon Sink in Rapidly Urbanizing Areas: A Case Study of the Yangtze River Delta Region

Abstract

Ecosystem carbon sinks are vital for mitigating global climate change. In the past two decades, the Yangtze River Delta (YRD) region has undergone rapid urbanization, with its carbon sink function undergoing significant changes. Understanding the spatial evolution patterns and formation mechanisms of ecosystem carbon sinks is critically important. Existing studies often examine single factors, lacking a comprehensive assessment of how natural and socioeconomic drivers interact through multiple pathways to influence carbon sink dynamics in rapidly urbanizing regions. This study quantifies the ecosystem carbon sink in the YRD from 2000 to 2020 using the Carnegie–Ames–Stanford Approach (CASA) and a soil respiration model, and examines its spatiotemporal evolution and driving mechanisms using Global Moran's I, hotspot analysis, Mann–Kendall trend analysis, and structural equation modeling (SEM). The results reveal three key findings: (1) The total carbon sink increased from 69.91 million tons (Mt) to 103.75 Mt, with high-value areas concentrated in mountainous regions characterized by favorable climatic conditions and dense vegetation, and low-value areas located in the east, primarily due to reduced ecological resource area and fragmented ecological structures from built-up land expansion; (2) Carbon sink functions improved across 68.45% of the region, particularly where vegetation matured, but declined in 15.67% of the region, mainly concentrated in regions of urban expansion; (3) SEM indicates that the normalized difference vegetation index (NDVI) and forest land proportion (PF) enhance carbon sink functions, while the proportion of built-up land (PBL), driven by population and economic growth, is the primary negative factor. This study underscores the importance of preserving ecosystem integrity and managing urban expansion to sustain carbon sink functions, offering scientific insights into balancing ecological conservation and development in urbanizing regions worldwide.