Abstract: Drawdown zones are recognized as significant methane (CH₄) emission hotspots within aquatic systems.Large reservoirs,such as the Three Gorges Reservoir (TGR),not only induce water level fluctuations locally but also profoundly alter the hydrology and carbon cycling of downstream river-connected lakes.This study investigated the relationship between CH₄ emissions from the TGR drawdown area and two major downstream lakes,Poyang Lake and Dongting Lake,following TGR impoundment.Through a comprehensive synthesis of regional CH₄ flux,water level,and water surface area data,the study quantified annual CH₄ emission changes.Results indicate that water-air interface CH₄ flux under flooded conditions was significantly higher than soil-air interface flux under non-flooded conditions (p<0.001),with overall flux aligning with subtropical monsoon climate temperature variations.The TGR drawdown area’s annual CH₄ emission was estimated at 1 200.71±135.13t,primarily from the water-air interface during the drawdown stage (Nov.-May) and soil-air interface during the main flood season (Jun.-Aug.).Conversely,post-impoundment,Poyang Lake’s annual CH₄ emission decreased by 414.10±164.49 t,and Dongting Lake’s by 2 959.27±1 176.96t.This reduction was largely due to the decreased inundated areas in both lakes during their peak water-air interface emission period (Jul-Nov).A significant seesaw-like relationship emerged,where the reduction in CH₄ emission from Poyang and Dongting Lakes markedly exceeded the increase from the TGR drawdown area (p<0.01).This dynamic is attributed to differential CH₄ fluxes between interfaces,TGR’s anti-seasonal regulation impacting downstream hydrology,and seasonal CH₄ flux variations.These results illuminate the mitigating effect of large reservoir impoundment on downstream methane emissions,offering a foundational basis for comprehensive assessment of the greenhouse effect of reservoirs.