Atmospheric Stilling Reshapes Algal Blooms and Eutrophication Risk in Shallow Lakes

Abstract Atmospheric stilling, defined as long‐term decline in wind speed, has emerged as a widespread climate signal, yet its role as an independent driver of eutrophication in shallow lakes remains poorly understood. Taking Lake Taihu as a representative case, we applied a coupled hydrodynamic‐ecological model (GOTM‐WET) to quantitatively estimate the impacts of declining wind speed on a large shallow lake, while keeping external nutrient loading constant. Model simulations showed that under a strong stilling scenario (45% wind reduction relative to the 2018–2022 baseline), mean surface water temperature increased by 1.96°C, while weakened vertical mixing reduced oxygen transport to bottom waters, resulting in a 56.2% decline in bottom‐water dissolved oxygen (DO). The development of hypoxic conditions intensified sediment anaerobic processes, enhancing internal phosphorus release while simultaneously accelerating denitrification‐driven nitrogen loss. These coupled biogeochemical responses drove a shift toward a phosphorus‐enriched and nitrogen‐depleted nutrient regime, fundamentally altering nutrient limitation patterns. Consequently, surface chlorophyll a (Chl a ) concentrations increased markedly, particularly in summer, with a mean enhancement of 45.4%, accompanied by more persistent and intense algal blooms, indicating pronounced seasonal differences in lake ecosystem responses to declining wind speed. Our results demonstrate that declining wind speeds modulate lake hydrodynamics, oxygen supply, and nutrient structure, driving coupled responses in lake temperature‐nutrient‐phytoplankton systems and markedly increasing the risk of eutrophication, highlighting atmospheric stilling as a previously underappreciated driver of the eutrophication risk in large shallow lakes under future climate change.