Nitrogen and submerged vegetation density drive metaphytic blooms in shallow lakes: an important hysteresis phase in regime shifts
摘要
Periphyton plays a critical role in the progress of the regime shift between macrophytes and phytoplankton in shallow lakes, since its overgrowth could trigger metaphytic blooms and lead to the collapse of submerged macrophytes. Understanding the mechanisms of metaphytic blooms and the subsequent prediction are important for lake managers to prevent ecological disaster. In this study, a one-year field survey on periphyton was conducted in Lake Ulansuhai to explore the driving factors of metaphytic blooms. The result revealed that the filamentous chlorophyta Mougeotia was identified as the key genus involved in metaphytic blooms. Structural Equation Modeling showed that Mougeotia biomass was positively correlated with total nitrogen, temperature, and submerged vegetation density. While phytoplankton biomass was primarily positively correlated with total phosphorus and temperature. A logistic regression model indicated that when the biomass of Mougeotia reached 1.78 g m−2 (95% CI 1.08–3.03 g m−2), the probability of metaphytic blooms exceeded 50%. These findings suggested that both nitrogen and phosphorus drive the regime shift, and a dual-nutrient-reduction strategy should be implemented during this hysteresis phase. Additionally, the biomass of submerged vegetation and water depth influence Mougeotia biomass. Therefore, controlling submerged vegetation and managing water levels are crucial in-lake strategies for mitigating metaphytic blooms.