Blue carbon ecosystems provide disproportionate carbon sequestration and biodiversity benefits, yet the long-term maintenance of these functions depends critically on their capacity to gain surface elevation and keep pace with sea-level rise. Vegetation promotes surface elevation change (SEC) in coastal wetlands by trapping sediment and accumulating organic matter, but the magnitude of this biogeomorphic effect remains insufficiently quantified in mangrove-saltmarsh ecotones subject to invasion and management. Here, we conducted a nine-year field observations in the Zhangjiang Estuary, China, using Surface Elevation Table-Marker Horizon (SET-MH) and UAV-based LiDAR to monitor elevation dynamics during the expansion and subsequent removal of invasive saltmarsh Spartina alterniflora. Our results show that after two removal events, SEC in S. alterniflora stands declined sharply from 26.47 mm/yr (Period 1) to 5.84 mm/yr (Period 2, -77.9%) and then to 1.37 mm/yr (Period 3, an additional -76.5%). Adjacent mangroves followed a similar but milder trend: from 14.98 mm/yr to 10.20 mm/yr (-31.9%) and then to 8.97 mm/yr (-12.1%). In contrast, mudflats progressively colonized by S. alterniflora but left unmanaged showed an initial SEC rise from 9.85 to 24.13 mm/yr (Period 2), then fell to 14.97 mm/yr (Period 3), reinforcing the vegetation-elevation link while hinting at later hydrodynamic shifts. Notably, SEC decline after each removal was far greater in S. alterniflora than in mangroves, indicating that mangroves continued to receive sediments originally trapped by the invader: upon removal of the outer‑edge S. alterniflora, sediments previously retained by the invader are hydrodynamically redistributed to higher‑elevation mangrove stands. Consequently, abruptly removing such an invasive engineer can destabilize elevation trajectories across linked habitats, with key implications for coastal wetland resilience under accelerating sea‑level rise.
Keywords: biogeomorphological process, biological invasion, Spartina alterniflora, surface elevation change, mangrove-saltmarsh ecotone, vegetation management