Ecological regime shifts and spatial heterogeneity in a large river-connected shallow lake over the past century

The ecological systems of large, river-connected shallow lakes, characterized by dynamic hydrological connectivity and intense flushing, exhibit distinct responses to global changes. Investigating the ways in which hydrological variability modulates ecological stability is vital for understanding alterations to lake ecosystems in an era of rapid environmental change. This study investigates centennial algal community dynamics in Poyang Lake, a typical river-connected lake system and Ramsar wetland. By integrating the paleolimnological records of geochemistry and diatom communities with high-resolution climatic and hydrological data, we reconstructed the ecological dynamics of two areas of this lake with contrasting hydrodynamic regimes. Our results showed that both regions underwent significant ecological transitions, moving from relatively stable states to increasing eutrophication pressure and declining ecological stability after the 1980s. The central region exhibited higher ecological resilience before transition, characterized by weaker coupling between diatom community changes and environmental variability, while the sub-lake system of Qinglan Lake showed a gradual nonlinear response to increasing environmental stress. However, the ecological dissimilarity between the two sites has narrowed over time, resulting in a marked decline in regional biodiversity and community heterogeneity in the new millennium. These trends were associated with the effects of hydraulic engineering, intensified land use, elevated nutrient loading and a climate warming. Generalized Additive Model (GAM) projections suggest that if the central lake area adopts the stagnant hydrological conditions currently observed in Qinglan Lake, planktonic algae are likely to proliferate at different rates in all warming scenarios, potentially triggering whole-lake blooms. This study offers critical insights into the drivers controlling the spatiotemporal heterogeneity of aquatic regime shifts, providing scientific insights for future ecosystem management.