Wetland changes of China's largest freshwater lake and their linkage with the Three Gorges Dam

The impoundment of the Three Gorges Dam (TGD) has led to significant inundation shrinkage and water level decrease in China's largest freshwater lake, Poyang Lake. However, little is known about the influence on the lake's wetland landscapes. Here, using Moderate Resolution Imaging Spectroradiometer (MODIS) observations and a phenology-based decision tree approach, we present the spatial and temporal changes of the major wetland cover types from 2000 to 2014. Over the 15-year period, both total coverage of vegetation (Carex spp., Triarrhena lutarioriparia L. - Phragmites, sparse grass, and Zizania latifolia communities) and the area of each community (excluding floating aquatic macrophytes community or FAM) showed significantly increasing trends, with vegetation expanded towards the lake center. In contrast, the areas of water and mudflat have decreased significantly since the TGD impoundment, and they were mainly replaced by prominently expanded vegetated areas. The transition maps during 2000–2014 show that the vegetation community transitions occurred mainly from hydrophilic cover types to those adapted to dryer conditions. Despite the significant changes in wetland cover types, the most preferable water depth for each cover type remained stable before and after the TGD. In conclusion, the vegetation compositions are primarily controlled by water depth, indicating that the recent wetland changes can be directly linked to the TGD-induced hydrological regime-shift. These results provide a critical reference for local authorities to assess the potential influence of the newly proposed dam in this lake and to optimize its future operations with respect to modulating water levels.