Hydrological connectivity associated with salinity mediates wetland vegetation pattern and productivity in estuary

Hydrological connectivity associated with salinity (termed water-salt connectivity) plays a critical role in estuarine ecological processes. Understanding the dynamic mechanisms through which water-salt connectivity influences vegetation is essential for effective coastal wetland conservation and restoration. This study establishes a Water-Salt Index of Connectivity (WSIC) model to investigate how intertidal vegetation distribution and development patterns respond to water-salt connectivity dynamics. Key findings reveal: (1) The WSIC model shows strong stability and significant correlations with measured soil salinity (P = 0.001), effectively characterizing intertidal salt transport and its associated heterogeneity; (2) Since 1987, rising-tide WSIC (WSIC_R) in the Yellow River Delta has declined 42 % (from -2.080 ± 1.037 to -2.973 ± 2.597, P < 0.001) with stable falling-tide WSIC (WSIC_F), signaling regional desalination; (3) Elevated WSIC corresponds to vegetation simplification and density reduction (P < 0.05). Species-specific adaptations drive zonal patterns, with vegetation transition zones shifting seaward due to intensified competition in high-WSIC areas; (4) WSIC regulates intraspecies biomass distribution, with Suaeda salsa displaying inverse correlations, others unimodal responses, indicating habitat contraction for S. salsa; (5) Reduced WSIC_R creates low-salinity niches for Spartina alterniflora invasion (P < 0.001), while increased salt retention post-invasion accelerates its expansion. Incorporating dynamic water-salt processes into ecological modeling, this research transcends conventional static environmental frameworks, providing actionable insights for wetland management, endemic species preservation, and invasive species control.