Identifying potential service flow and actual service flow: Source-flow-sink-use framework and case study

Clarifying the delivery chain of ecosystem services (ESs) from generation to transfer to utilization is the basis for conducting ecosystem service flows (ESFs) assessment and management. However, spatial characteristics and interconnections in the delivery chain have not received sufficient attention. Here, we proposed a source-flow-sink-use framework and distinguished between potential service flow and actual service flow. Based on this, we quantified the supply, demand, potential flow, actual flow, flow depletion and storage of freshwater supply service (FS) at the pixel, township, and county scales in the Ning-Zhen-Yang region in 2023. Then, we improved freshwater security indexes (FSI) and constructed regional freshwater supply security pattern. The results showed that potential service flow exhibited a west-low, east-high pattern, while actual service flow was significantly lower and displayed greater spatial heterogeneity. Static FSI, potential FSI, and actual FSI demonstrated freshwater supply security patterns of slight surplus, surplus, and southern surplus with northern deficit, respectively. Furthermore, we discussed the applicability, classification, quantification, and application of the source-flow-sink-use framework, and explored the implications of the study results for spatial planning or ecosystem management. This study enriches the assessment framework for ESFs and provides a basis for constructing application pathways oriented toward ecological processes.