Cascading River‐Lake Hydrological Regulation Reshapes Carbon Budgets of Floodplain Lakes in the Yangtze River Basin

Abstract

The carbon budget of floodplain lakes is regulated by natural hydrological processes, yet the role of human interventions, including cascade river‐lake hydraulic projects, remains unclear. We evaluated the combined effects of the Three Gorges Dam (TGD) located on the Yangtze River and the proposed lake‐specific hydraulic projects (LHPs) on the carbon budgets of the respective Dongting and Poyang Lakes downstream of the TGD. As a result of TGD's operation, Dongting Lake saw a weakened carbon sink, with carbon dioxide (CO ₂ ) uptake reduced by 6% and methane (CH ₄ ) emissions increasing by 4%. The opposite is true for the downstream Poyang Lake, with CO ₂ uptake increasing by 8% and CH ₄ emissions decreasing by 1%. This divergence stems from the lake‐specific vegetation composition and TGD's regulation strategy. The Phragmites in Dongting Lake is sensitive to hydrological regulation during the pre‐flooding seasons, while the Carex in Poyang Lake is sensitive to hydrological regulation during the post‐flooding seasons. In contrast, the operation of LHPs will uniformly reduce the carbon sink due to elevated lake water levels, leading to a sharp decline in CO ₂ uptake in Poyang Lake (36.98 gC m ⁻²  yr ⁻¹ ) and Dongting Lake (11.87 gC m ⁻²  yr ⁻¹ ). A cascade operation of these projects will increase the global warming potential (GWP) by 0.88 Tg CO ₂ eq yr ⁻¹ . Our findings underscore the necessity of integrating ecological consequences into water resources management to reconcile water security with climate stability goals.