Analysis of spatiotemporal changes and driving factors of green and blue carbon stocks in Zhangzhou City based on PLUS and InVEST models

As two major carbon pools in the earth's ecosystem, green and blue carbon have great carbon sink potential, and the study of carbon stocks is of great significance for protecting the ecosystem and enhancing the carbon sink potential. Land use is the main factor affecting the change of carbon stocks, and the study on the changes of land use is helpful to the realization of China's “Dual-Carbon” Policy. This study focused on Zhangzhou City and its coastal mangrove nature reserve in Fujian Province, China, and estimated the green and blue carbon stocks in 2000–2020 via the InVEST and PLUS models to analyze their spatiotemporal change characteristics and potential driving factors. Additionally, this study also predicted changes in carbon stocks in 2030 and 2050 through different scenario simulations to provide a scientific basis for achieving the goal of China's “Carbon Peak, Carbon Neutrality”. The study found that from 2000 to 2020, the green carbon stocks in Zhangzhou City decreased by 15.62 × 10⁴ t, with a gradually increasing amplitude, while the blue carbon stocks in the Zhangjiang Estuary Mangrove Nature Reserve and Jiulongjiang Estuary Mangrove Nature Reserve increased by 9.79 × 10⁴ t and 17.15 × 10⁴ t respectively, with a decreasing amplitude. Land use changes are mainly driven by natural factors (i.e. altitude, average annual precipitation) and socio-economic factors (i.e. GDP, population density). The blue carbon ecosystem, especially mangroves, shows much higher carbon sink potential than the green carbon ecosystem. However, the invasion of the alien species Spartina alterniflora leads to a sharp decrease in the area of mangroves, significantly affecting the blue carbon stocks. The results of this study show that if ecological protection measures are not taken, the green carbon stocks in Zhangzhou City will continue to decline, and the increase of blue carbon stocks will be further reduced. Therefore, strengthening the protection of woodlands, reducing the disturbance of human activities and preventing and controlling the invasion of alien species are the key strategies to achieve the improvement of regional carbon stocks.