Impacts of Extreme Flood and Drought Events on Dish-Shaped Lakes Habitats in Poyang Lake Under Altered Hydrological Regimes

As typical river-connected wetland lakes in the middle and lower Yangtze River basin, the dish-shaped lakes (DSLs) of Poyang Lake have experienced significant impacts on ecosystem stability and regional biodiversity due to the increasing frequency of extreme hydrological events and altered hydrological regimes in recent decades. This study systematically analyzed the effects of new hydrological regimes and extreme hydrological events on the coupled hydro-ecological evolution of DSLs under different sluice-controlled conditions, utilizing long-term water level data from the Xingzi Station, multi-source remote sensing images, and field survey data. The results revealed that: (1) Post-2003, regional water levels exhibited a significant decline (monthly decrease of 0.84 m), with prolonged water level duration shifting from the 10.0–14.0 m range to lower intervals (6.0–10.0 m). Extreme hydrological events triggered notable succession of beach wetland vegetation and a "collapse-recovery" dynamic in submerged vegetation by altering water levels, inundation extent, and duration. (2) Compared to non-Gate Controlled DSLs (non-GC DSLs), Gate control DSLs (GC DSLs) effectively mitigated ecological impacts from extreme events through water level regulation, prolonging the autumn retreat phase (water area change rate: -0.312 km²/d), suppressing downward expansion of emergent/hygrophytic vegetation along elevation gradients during high-water level years, and stabilizing vegetation habitats in low-water level years. However, regulatory strategies and underlying surface characteristics could drive divergent habitat evolution. (3) Habitat heterogeneity induced by vegetation community reorganization along elevation gradients differentially influenced wintering waterbirds: foraging patterns of wading birds (e.g., Siberian Crane) shifted due to reduced Vallisneria spp. coverage, while goose and duck species feeding on Carex spp. were less affected. GC DSLs provided relatively stable habitats and food resources during extreme hydrological events. The study proposes a tiered dynamic regulation strategy to balance natural hydrological fluctuations with artificial interventions, enhancing the resilience of DSL wetlands against extreme hydrological disturbances.