Spatial Characteristics and Driving Forces Analysis of Water Conservation Services in Coastal Plain Cities—Yancheng as an Example

The stability of ecosystems in coastal plain cities is fragile, and the interaction between humans and the land is complex, making the region’s natural water cycle capabilities more vulnerable to destruction. Quantitatively assessing the water conservation services in coastal areas and revealing its spatial characteristics and driving factors play a crucial role in the construction of regional ecological barriers and the assurance of ecological security. In this study, based on the water balance model, the spatial dynamics of water in the ecosystems of Yancheng from 2019 to 2021 were assessed in two dimensions: ecosystem and administrative subdivision. The response of the influencing factors to the water conservation was examined using a geographical detection. The results show the following: (1) Yancheng’s water conservation services increased (2019–2021), averaging 1.188 × 109 m3/a. Spatially, it was higher in southeastern/northern sectors and lower in western/central regions, with wetlands and croplands contributing 93.76% collectively while others each accounted for <1%. (2) NDVI was the strongest driver of spatial heterogeneity (q = 0.736), followed by per capita water use, population density (q = 0.642), and DEM (q = 0.638); GDP per capita and annual precipitation exerted the weakest influences. (3) Factor interactions exceeded individual factors in explanatory power, dominated by population density synergies with per capita water use and NDVI, which most strongly controlled spatial patterns. (4) Optimization thresholds were identified: peak water conservation occurred at DEM 5.34–5.47 m and NDVI 0.37–0.42. This study provides a new perspective on water conservation in coastal areas, supplying serves as a reference for crafting specific water preservation strategies in the coming years.