Ecosystem service flow dynamics across a Mountain-Oasis-Desert system: spatial flow patterns and driving forces in the Heihe River basin, China

Arid and semiarid inland river basins are characterized by fragile ecosystems and pronounced ecological gradients, where limited water availability constrains ecosystem services (ESs) provision and results in persistent spatial imbalance between supply and demand. Current research, largely focused on static supply-demand patterns, often neglects the redistributive role of ecosystem service flows (ESFs) in alleviating spatial mismatches. To address this gap, this study focuses on the Heihe River Basin (HRB), develops an integrated framework that combines ES supply-demand assessment, spatial flow simulation, and machine-learning-based attribution analysis to quantify the spatial flow patterns of food production (FP), water conservation (WC), soil conservation (SC), and sand fixation (SF) across the mountain-oasis-desert composite system, and investigate their dynamic coupling with regional socioeconomic driving factors. The results indicate that: (1) The ESDR of four ESs exhibit persistent spatial heterogeneity along the mountain-oasis-desert gradient, with FP showing continuous improvement, WC experiencing a deepening deficit, SC showing slight alleviation, and SF remaining persistently deficient. (2) FP flows mitigated supply-demand imbalance through multi-source convergence (3.68 × 10 11 kcal max), whereas WC flows regulated downstream deficits via continuous upstream-downstream transfer (maximum 9.12 × 10 7 m 3 ). SC flows showed significant localized regulation, while SF flows acted as a directional protective flow toward downstream desert area, both limited by weak cross-regional redistribution. (3) The effects of different driving factors on ESFs exhibit significant heterogeneity, with the driving mechanism shifting from natural-factor dominance toward a coupled socio-ecological system. FP flows increasingly responded to socio-economic factors, whereas SC flows and SF flows were primarily dominated by vegetation and topography, and WC flows were jointly regulated by drought stress, land use, and human demand. This study reveals the pivotal role of ESFs in alleviating supply-demand mismatches along ecological gradients in arid and semiarid regions, offering scientific support for differentiated ecosystem management strategies through cross-regional coordination of transferable services and targeted ecological conservation of key source areas providing protective services.