关键词: 潮滩, 遥感, 形变监测, 关键驱动, 茅尾海

Abstract:

Tidal flats are transitional areas where land meets the sea and play a crucial role in maintaining the health of coastal ecosystems and in sequestering blue carbon. With the challenges posed by global sea-level rise, increased human activities, and frequent natural disasters, there is an urgent need for effective monitoring and analysis of the spatial and temporal distribution, as well as the surface deformation, of tidal flats. This study focuses on the coastal zone of Maowei Sea in the Beibu Gulf, China. By integrating Sentinel-2 imagery from 2015 to 2023 with low-tide Sentinel-1 imagery and various other data sources, including sea-level changes, precipitation, and hydrological variations, the following investigations were conducted: ① Employing the Google Earth Engine (GEE) cloud platform, this study used time-series Sentinel-2 imagery along with the enhanced mangrove vegetation index (EMVI), normalized difference water index (NDWI), the maximum spectral index composite (MSIC) algorithm, and Otsu's method (OTSU). This approach successfully identified intertidal flats within the study area. Results demonstrated an overall accuracy of 96.6% and a Kappa coefficient of 0.92, confirming the reliability of this identification method. The tidal flat area in Maowei Sea decreased from 19.98 km² in 2016 to 15.80 km² in 2023, a 20.9% reduction. Land use types shifted from tidal flats to mangrove forests, construction land, and other categories. ② A deformation extraction method termed “PS+SBAS-InSAR” was developed, incorporating partial permanent scatterers (PS) into small baseline subset synthetic interferometric aperture radar (SBAS-InSAR) technology to monitor tidal flat deformation. Results show that between 2015 and 2023, the surface deformation rates on the tidal flats ranged from－54.72 mm/a to 41.71 mm/a. During this period, 98.77% of the area experienced deformation rates between－20 mm/a and 20 mm/a, and 84.62% of the area had rates between－10 mm/a and 10 mm/a, indicating overall stable ground deformation. The most significant subsidence was observed at Mangrove Bay, with a cumulative total of－308.21 mm, while the highest uplift occurred at Kangxi Ridge, with a cumulative total of 311.90 mm. The tidal flats of Maowei Sea show uneven deformation patterns, mainly characterized by slight uplift. Specifically, subsidence occurs along both banks of the Jianshan River and in Hongshu Bay, while uplift is observed at Kangxi Ridge and in the northwestern part of Jianshan. Irregular uplift and subsidence patterns are evident along both banks of Longmen Qishierjing. ③ Comprehensive analysis of multiple data sources shows that precipitation, hydrological movement, sea-level rise, and mangrove changes are the main factors affecting tidal flat surface deformation. Sea-level rise is negatively related to this deformation. Precipitation and extreme-weather patterns are seasonal, while mangrove dynamics, sea-level rise, and coastal aquaculture have long-term effects.

Key words: tidal flats, remote sensing, deformation monitoring, key drivers, Maowei Sea