Creek‐imposed gradients reshape plant allometric traits and sediment retention in a salt marsh

Tidal creeks impose strong hydrological and geomorphic gradients that shape plant traits and sediment dynamics in salt marshes. However, how creek‐imposed gradients reorganize plant allometric strategies and how these trait shifts regulate sediment retention remain poorly quantified. We conducted field surveys and sediment measurements along cross‐creek transects in the Chongming Dongtan salt marshes (Yangtze River Estuary) to examine spatial variation in vegetation traits, environmental conditions, and sediment processes. Using generalized linear models (GLMs), non‐parametric local regression (LOESS), and Gaussian nonlinear fitting, we quantified relationships between plant allometry, vegetation density, and suspended sediment concentration, net sediment deposition, and sediment retention rate. Plant traits varied systematically with distance from tidal creeks: aboveground biomass of the pioneer species Scirpus mariqueter near creek edges was approximately 2.6‐fold higher than at 30 m inland, while stem height–diameter relationships shifted from structural reinforcement near creeks to height investment farther from creeks, reflecting allometric trade‐offs along hydrodynamic stress gradients. Sediment retention exhibited a clear nonlinear response to vegetation density, peaking at intermediate densities (~1000–1500 shoots/m 2 ). These results demonstrate that tidal creeks act as trait‐based filters that generate emergent, nonlinear sediment retention patterns, providing mechanistic insight into biogeomorphic self‐organization and quantitative guidance for nature‐based salt marsh conservation and restoration.