Vigilance against climate change-induced regime shifts for phosphorus restoration in shallow lake ecosystems

The dual pressure of anthropogenic activities and frequent extreme weather events has triggered a transition from macrophyte to algal dominance in shallow lakes. Phosphorus (P) is the key driver of regime shifts that can lead to a decline in the stability and resilience of lake ecosystems. However, the mechanisms underlying such regime shifts, and the effects of state transitions on internal P loading during macrophyte restoration in large shallow eutrophic lakes, remain to be fully elucidated. This study utilised long-term in situ monitoring data, across three distinct lake states (bare ground, macrophyte-dominated stage, and algae-dominated stage) to elucidate the accumulation and release mechanisms of sedimentary P during regime shifts. The findings demonstrated that the rehabilitation of submerged plants efficiently reduced internal P loading (water column P, sediment P fractions, and P flux), while the persistence of algal blooms was driven by the reductive release of Fe-P from sediments and the dissolution of Al-P from suspended particulate matter. High temperature, low dissolved oxygen, and high pH largely modulate the pathways and mechanisms of P supply during regime shifts. The combined pressures of extreme weather (heavy rainfall, strong winds, and extreme heat) and trophic cascades from fish stocking can trigger a shift from macrophytes to algae in shallow lakes. Appropriate management of the structure and biomass of aquatic animal communities (e.g., small-bodied or omnibenthivorous fish) and optimization of the food web structure can effectively improve water quality and maintain ecosystem stability. These findings enrich the theoretical understanding of regime-shift mechanisms from an ecosystem perspective and offer novel insights into P remediation in large shallow eutrophic lakes.