Coastal salt marshes are critical blue carbon sinks but are threatened by coastal reclamation and biological invasion. Conventional discrete mapping lacks temporal continuity, limiting assessments of long-term successional pathways and carbon dynamics. We developed an integrated long-term remote sensing framework using the Landsat archive (1986–2023) to quantify salt marsh dynamics and carbon burial in Hangzhou Bay, China. The framework integrates optimal phenological window selection, continuous change detection, and Random Forest classification to generate accurate annual species-level maps. From 1986 to 2023, salt marshes underwent multi-phase transitions, progressing through natural succession to reclamation-driven coastal squeeze and subsequent invasion-led reorganization. Total wetland area declined by 60%, reflecting the net effect of massive reclamation (893.6 km²) against vegetation expansion. Bare mudflats decreased by 73%, native Scirpus mariqueter by 27%, and invasive Spartina alterniflora expanded by 174%. These transitions led to 49% reduction in annual blue carbon burial (from 71.1 to 36.4 Gg C yr−1). Despite recent invasive expansion and stricter reclamation controls, carbon burial recovery remained limited, reflecting the reclamation’s dominant influence on long-term losses. This study provides a scalable framework for continuous monitoring of salt marsh dynamics and quantifies carbon burial responses to anthropogenic and biological pressures in highly modified estuarine ecosystems.
Cao et al. (Tue,) studied this question.