Spatial and Temporal Variation in Drivers of Saltmarsh Eco‐Geomorphic Evolution: Field Insights From the St. Lawrence Estuary, Canada

ABSTRACT Predicting the long‐term evolution of saltmarshes using numerical tools could significantly aid management and restoration efforts. However, limited geographic diversity in the present body of saltmarsh eco‐geomorphic literature highlights a significant barrier to model development and widespread application. To address this gap, a comprehensive field study was conducted for meso‐tidal saltmarshes within the St. Lawrence Estuary (Petites‐Bergeronnes, Québec, Canada). From eight field campaigns performed between July 2023 and August 2024, a novel hydro‐eco‐geomorphic database is presented for the study site. Spatial variation in eco‐geomorphic drivers supported observations of contrasting historical marsh edge evolution; differences in inundation frequency, sediment supply, deposition rates and vegetation properties are reinforcing marsh progradation in one area of interest, and edge erosion within another. Within the former, suspended sediment concentration was significantly correlated with temporal variation in spring tidal heights, indicating that short‐term hydrodynamic changes could critically influence sediment supply. Analysis of stem measurements for seven saltmarsh species demonstrated a significant difference in stem length and diameter between pioneer ( Sporobolus alterniflorus ) and high marsh communities ( S porobolus pumilus – and Plantago maritima –dominant). Repeated measurements throughout the snow‐free season also revealed significant temporal variation in stem properties, often disregarded in numerical models. Pioneer S. alterniflorus exhibited the largest magnitude of change, with increases of 2.53 mm in mean diameter and 59.5 cm in mean length between early and peak season. Overall, this work presents important advancements for system understanding of saltmarsh evolution across diverse geographies and provides novel datasets for addressing spatial and temporal complexity in eco‐geomorphic processes.