Integrating hotspots, trade-offs and bundles to reveal the spatial interactions among four water-related ecosystem services for systematic watershed management

China is committed to advancing the integrated governance reform of water resources, water environment, and water ecology (Three Water Integration, TWI), aiming to enhance the effectiveness of systematic watershed management. However, interaction analyses of TWI that rely on static element coupling remain inadequate for comprehensively supporting the demands of systematic watershed management. This study reveals the spatial interactions within TWI by analyzing the cold and hotspots, trade-offs and synergies, and bundles of water-related ecosystem services (WESs), through the dimensions of multifunctionality, correlation, and dominance. The results indicate significant differences in temporal variations, structural ratios, and spatial distributions among the four types of WESs, namely water provisioning, water purification, soil conservation, and flood regulation. Although the hotspots of individual WES exhibit significant spatial heterogeneity, the spatial overlap of multiple WESs hotspots encompasses 23.68 % of the watershed area, thereby identifying multifunctional ecological priority conservation zones. Six distinct trade-off and synergy relationships among WESs are identified, with synergies comprising two-thirds, highlighting their potential to support win-win outcomes in TWI implementation. Four functional areas with distinct dominant WESs are identified, corresponding to the low-level balanced bundle of WESs, the water purification-water provisioning synergy bundle, the soil conservation-water provisioning synergy bundle, and the flood regulation-water provisioning synergy bundle. Through quantitative characterization the spatial interactions of WESs, this study provides a new perspective for the systematic advancement of watershed TWI management.