Understanding ecosystem service flows through the metacoupling framework

Ecosystem service (ES) flow is an indispensable link between natural ecosystem and socioeconomic system. Research on ES flow is of great significance for regional ecosystem management and ecological compensation policies. However, previous studies have mainly focused on ES flow within a region or ES flow across regions, without distinguishing the relationship between ES flow within a region and ES flow from the region to its external regions. Therefore, taking the Huangshui River Basin in the Tibetan Plateau as an example, we combined the revised equivalent factor method and the breaking point model to analyze the ES flow within the basin and ES flow between the basin and its external regions (including adjacent and distant systems) under the metacoupling framework. The results showed that ES flow within the basin, ES flow to adjacent systems and ES flow to distant systems decreased from 2000 to 2020. ES flow to distant systems decreased the most, with an average decrease of 666 million yuan. Moreover, among different ESs, the decrease in hydrological regulation flow to the distant system was the most substantial, at least 2.4 times that of other ESs. Grassland loss in the basin was the main reason for the decrease in hydrological regulation flow to distant systems. Therefore, we suggest that future ecosystem conservation in the basin needs the participation of distant systems to ensure the ESs provided to them. Following the basic principle of "who benefits, who compensates", distant systems that benefit can establish the grassland ecological compensation mechanisms to maintain the hydrological regulation service flowing to them, thereby ensuring water security and promoting sustainable development.