Spatio-temporal Evolution Characteristics of Wetland Aquatic Vegetation in Hongze Lake and Its Relationship with Hydrological Regimes

Hongze Lake, the fourth largest freshwater lake in China, plays a crucial role in flood control, drought mitigation, and water supply in the lower reaches of Huai River basin. It also serves as a regulating reservoir along the eastern route of the South-to-North Water Diversion Project, exerting significant influencing on the region's sustainable economic and social development. Aquatic vegetation constitutes an essential component of the lake's ecosystem, actively contributing to maintaining ecosystem health and preventing ecological risks. Based on Landsat imagery data from 1985 to 2023 and using a random forest classification algorithm, this study extracted spatiotemporal distribution of emergent vegetation, submerged vegetation, aquaculture zones and open-water areas in Hongze Lake. It further analyzed the long-term temporal characteristics, trends, and patterns of aquatic vegetation changes, examined hydrological dynamics, and revealed their linkages with vegetation evolution. The study yielded the following key findings: (1) Wetland aquatic vegetation showed an overall declining trend, with submerged vegetation decreasing by more than 80%. Aquaculture areas first expanded and then decreased, while the extent of emergent vegetation remained relatively stable; (2) Aquatic vegetation shifted from lakeshore zones dominated by emergent vegetation towards open water zones suitable for submerged vegetation, forming a distinct zonal distribution pattern. The spatial distribution of emergent and submerged vegetation exhibited strong heterogeneity, with pronounced fragmentation of vegetation zones after 2010; (3) The hydrological regime of Hongze Lake displayed an inverse seasonal fluctuation, with high water levels in winter and spring and low water levels in summer. Higher average water levels during the storage period suppressed the growth of submerged vegetation, whereas relatively high flooding frequency (0.6–0.8) prompted its expansion. Based on these findings, the study recommends strengthening the rehabilitation of wetland aquatic vegetation in lakeshore zones and restoring vegetation in key areas, promoting the conversion of reclaimed land back to the lake and the ecosystem reconstruction, and improving management frameworks for precise regulation. These efforts aim to support the restoration and conservation of the Hongze Lake wetland ecosystem. This study explores the spatiotemporal evolution of wetland aquatic vegetation in Hongze Lake and its relationship with hydrological regimes, serving as an initial step in advancing research on lake ecological conservation and restoration.