Assessing land carbon metabolism in the Hubei Section of the Three Gorges Reservoir Area based on ecological network

Revealing the relationship between carbon metabolism and carbon balance in human-nature coupled systems is vital for achieving China's "dual carbon" goals. With land use types as metabolic entities, we constructed a carbon metabolism spatial network model by measuring vertical carbon emission, carbon absorption, and horizontal carbon flow, and systematically explored the carbon metabolism evolution of the Hubei section of the Three Gorges Reservoir from 1995 to 2020. We further assessed ecological relationship, integral utility, and node contributions of the carbon metabolism spatial network by the ecological network analysis method, and comprehensively evaluated the impact of land use on regional carbon metabolism. The results showed that carbon emissions in the vertical direction increased from 1.0143 million tons in 1995 to 2.9177 million tons in 2010 and then stabilized, mainly from carbon emission associated with industrial and transportation land. Carbon absorption remained stable at approximately 5.3 million tons, with forests being the main carbon sink. In the horizontal direction, the net carbon flow remained negative. The negative carbon flow mainly resulted from the occupation of forest and cultivated land by industrial and transportation land around county urban areas. The submergence of forest and cultivated land by water along the Yangtze River, as well as the conversion of forests to cultivated land at the southern border of Xing-shan County and the junction with Zigui County, resulted in negative carbon flow. The positive carbon flow mainly resulted from the conversion of cultivated land back to forest. Among the metabolic entities, ecological relationships were dominated by exploitation and restriction due to industrial and transportation land, as well as competitive relationships among the natural metabolic entities. The integral ecological utility index of land carbon metabolism network was below 1, indicating that land use exerted a negative effect on carbon metabolism in the reservoir area. Forests, water, and other producers contributed the most to maintaining the balance of the carbon metabolism network. The increasing weight of industrial and transportation land, and urban land affected the structural rules of the carbon metabolism network, which was detrimental to the carbon metabolism balance in reservoir area.