Machine learning-based mapping wetland dynamics of the largest freshwater lake in China

Lake wetlands are critical components of freshwater ecosystems, providing crucial roles in water regulation and biodiversity conservation. However, these lake wetlands are experiencing pervasive and often irreparable losses due to anthropogenic activities and climate change. This study utilizes remote sensing imagery from 1987 to 2023 based on a machine learning technique to analyze the dynamic changes in the wetlands of Poyang Lake, the largest freshwater lake in China. The results revealed a substantial decline in Poyang's wetland area, totaling 242.71 km² over the study period. The mudflat areas within the wetlands demonstrated a marked reduction of 64 %, equating to a loss of 617.60 km², predominantly in the northern zone of the lake. In contrast, vegetation coverage increased significantly by 36 %, rising from 1035.32 km² in 1987 to 1411.99 km² in 2023, characterized by a net gain of 361.05 km² primarily due to the encroachment of mudflats. Increases in rainfall have expanded water bodies in dish-shaped lakes, encroaching on the transitional mudflat areas, thus exacerbating wetland degradation. Additionally, intensified human activities, particularly the construction of the Three Gorges Dam, have profoundly altered the river-lake topography gradient and enhanced Poyang Lake's discharge capacity into the Changjiang River. This alteration appears to be a primary driver of the observed vegetation expansion. Concurrently, reservoir construction within the Poyang Lake basin has trapped water and sediment, and sand extraction within the lake basin has water and sediment entrapment, exacerbated by sand extraction activities that have directly diminished mudflat areas. The present work highlights the ongoing degradation trends of lake wetlands and elucidates the driving forces behind the evolution of Poyang Lake, providing valuable insights for management and conservation strategies aimed at promoting the restoration and sustainable development of lake wetlands.