A Threshold-Based Framework for Spatial Pre-Assessment of Coastal Salt Marsh Restoration Suitability

Coastal salt marsh restoration can support blue carbon sequestration, but spatial pre-assessment is needed to identify where environmental conditions support vegetation establishment before restoration design and carbon accounting. This study developed a threshold-based framework for spatial pre-assessment of coastal salt marsh restoration suitability. The framework combines species-specific limits for tidal inundation duration, seawater salinity and sediment salinity with sediment type in a geographic information system workflow. Tidal inundation limits are translated into critical-elevation boundaries, and retained polygons are examined against planning, historical-distribution and use-right conditions. A general threshold library was compiled for five representative native salt marsh species, while regional records define the candidate set for each application. In Yingkou, China, Suaeda heteroptera and Phragmites australis formed the candidate set. For S. heteroptera, the 3 h d−1 inundation limit corresponded to a critical elevation of 1.90 m. July 2024 sediment salinity (0.96–1.08%) and September 2025 seawater salinity (29.715–29.825‰) met the corresponding screening limits for S. heteroptera and excluded P. australis. The integrated restoration-suitability area covered 76.5 ha, and 99.5% of the mapped current S. heteroptera distribution fell within it. The framework identifies candidate restoration space for field verification, restoration planning and subsequent carbon accounting.