Spatial intrinsic interconnections and feedback effects between water-related ecosystem services supply and demand changes: a spatial bidirectional coupling-feedback analysis framework

Watershed management requires evaluating ecological service supply alongside human demand, yet basin totals can conceal contrasting patterns in water provision, erosion control, and nutrient export. We assessed the Yangtze River Basin from 2000 to 2020 by combining InVEST estimates of water yield (WY), soil conservation (SC), and nitrogen export (NE) with demand proxies, including an allowable-load proxy for nitrogen-related comparison, Getis–Ord Gi* change maps, normalized supply–demand overlays, and optimal-parameters-based geographical detector (OPGD) analysis on a common 3-km grid. WY increased from 1,186.46 × 10 9 to 1,538.51 × 10 9 m 3 , SC from 52.8 × 10 9 to 57.9 × 10 9 tonnes, and NE declined from 0.177 × 10 9 to 0.165 × 10 9 tonnes. WY demand increased from 174.80 × 10 9 to 207.51 × 10 9 m 3 , and the SC-demand proxy from 1.0 × 10 9 to 1.2 × 10 9 tonnes. The strongest spatial associations were SC in L–L (q = 0.1423), NE in M–M (q = 0.1702), and WY in H–H (q = 0.3083). Construction-land, population, and GDP showed stronger q values in 2010–2020 than in 2000–2010. These findings support targeted water-use efficiency, erosion-control, and nutrient-load management across distinct basin regions.