Tall salt marshes play a crucial role in the long-term geomorphic evolution of the Jiuduansha wetland, Yangtze estuary, China

Abstract

Salt marshes play a pivotal role in shaping coastal wetlands by influencing hydrodynamics and sediment transport, a topic that has garnered increasing attention in recent studies. However, the specific roles of different vegetation types in driving geomorphic evolution remain unclear. This study aims to assess the impact of varying salt marsh vegetation on the long-term geomorphic evolution of coastal wetlands. Using 1449 satellite images spanning 39 years (1984–2023) from the Google Earth Engine data archive, we investigated how different salt marsh types influences geomorphic changes on Jiuduansha Island, the largest uninhabited island in the Yangtze Estuary, China. Our analysis focused on the long-term salt marsh expansion and geomorphic evolution of Jiuduansha. The results revealed that the total area of Jiuduansha, as well as the extent of tall salt marshes, has increased significantly over the past decade. Notably, tall salt marshes exert a profound influence on geomorphic evolution. Specifically, in the accretionary sections of Jiuduansha Island, the natural expansion of tall salt marshes (Spartina alterniflora and Phragmites australis, with mean heights of 1.8 m and 2.5 m, respectively) drives seaward progradation. Conversely, in erosional sections, these tall salt marshes play a crucial role in mitigating further shoreline erosion. This study underscores the significant role of tall salt marshes in the long-term geomorphic evolution of coastal wetlands, offering valuable insights into the dynamics of wetland ecosystems and their resilience to environmental changes.