Multi-decadal Dynamics of Regime Shifts in Dianchi Lake: Drivers and Restoration Implications for Plateau Shallow Lakes

• Dianchi Lake underwent an abrupt regime shift from macrophyte-dominated clear water to algae-dominated turbid water over 40 years. • Pinpoints hydrodynamic disturbance, nutrient imbalance, and sediment legacy as core drivers shaping plateau lake ecosystem stability. • The shift was driven by a feedback loop: hydrodynamic light limitation, nutrient enrichment (N/P), and sediment bioavailable nitrogen. • A conceptual framework for plateau shallow lakes highlights the synergy of physical, chemical, and sedimentary processes. • Integrated management combining external nutrient reduction, internal load and hydrodynamic control is essential for restoration. As a representative large shallow lake on the Yunnan-Guizhou Plateau, Dianchi Lake has experienced severe ecological degradation primarily driven by eutrophication. This study systematically investigates the spatiotemporal evolution and driving mechanisms of the macrophyte-algae ecosystem in Dianchi Lake, utilizing remote sensing data (1987-2022), historical monitoring records, and a comprehensive field survey conducted in 2022. The results demonstrate that since the 1970s, Dianchi Lake has experienced an abrupt regime shift from a macrophyte-dominated clear-water state to an algae-dominated turbid-water state: submerged vegetation coverage declined sharply from 90% in the 1960s to virtually 0% by the 2010s, while the algal bloom area peaked at 41.07 km 2 in 1998 and 54.11 km 2 in 2007. Although the extent of algal blooms has diminished in recent years, periodic outbreaks continue to occur. Mechanistic analysis indicates that the decline of submerged plants was initially triggered by hydrodynamically induced light limitation. Subsequent nutrient enrichment and stoichiometric imbalance further accelerated the establishment of an algae-dominated state through a self-reinforcing “nutrient-algae-turbidity” feedback loop. Additionally, bioavailable nitrogen stored in the sediments contributed to the persistence of turbidity. The interplay of multiple stressors, combined with ecological hysteresis, complicates the ecological restoration of Dianchi Lake. The conceptual framework of regime shifts in shallow plateau lakes proposed in this study highlights the critical need for integrated management strategies that combine external nutrient reduction with internal load control and hydrodynamic regulation. These insights provide a theoretical foundation and practical guidance for the ecological management of similar lakes worldwide.