Spatiotemporal evolution of typical silt-muddy coastlines and tidal flats and their response to human activities: A case study of the Yancheng Coast, China

In response to the research gaps regarding the response mechanisms of muddy coasts to human activities, this study focuses on the Yancheng coastal zone, a typical muddy coast in China, to quantify the spatiotemporal evolution patterns of the coastline and tidal flats and reveal their feedback mechanisms with human activities, thereby providing decision-making support for the sustainable development of coastal zones. Based on eight periods of Landsat remote sensing images (totaling 16 scenes) from 1990 to 2024, this study extracted instantaneous waterlines using the Normalized Difference Water Index (NDWI) and Canny edge detection, determined the coastline through tidal level interpolation discretization and visual interpretation, calculated coastline change rates using the Digital Shoreline Analysis System (DSAS), constructed the Human Activity Intensity of Land Surface (HAILS) index, and employed Redundancy Analysis (RDA) to analyze the relationship between human activities and coastal changes. The results indicate: (1) Over the 34-year period, the total length of the Yancheng coastline increased from 333.09 km to 339.89 km, with the proportion of artificial coastline rising from 12.03 % to 48.11 %. The Sheyang River serves as a boundary, with the coastline changes adhering to the “southern accretion and northern erosion” pattern, where the maximum erosion rate reached 33.7 m/a and the maximum accretion rate was 380 m/a. Tidal flat area changes exhibited a “southern decrease and northern increase” trend. (2) The intensity of human activities in the coastal area increased from 0.16 % to 0.22 %, with the equivalent area of construction land expanding by 270.46 km², where the growth of construction land and aquaculture ponds was most significant, while the reduction in tidal flat area was most pronounced. (3) There exists a positive synergistic enhancement between coastline change intensity, artificialization index, and human activity intensity, whereas tidal flat area shows a significant negative response to human activity intensity. The “southern accretion and northern erosion” pattern in the Yancheng coastal zone results from the interaction between human activities and natural processes. This study provides new research perspectives on balancing the appropriateness of reclamation, coastline stability, and coastal ecosystem diversity in typical muddy coasts.