China's lakes remain carbon sources: Insights from the balance between intrinsic carbon sequestration and emissions.

Accurate assessments of lake carbon balance are essential for filling gaps in the global carbon budget and addressing climate change. However, persistent uncertainties arise from an incomplete understanding of intrinsic carbon sequestration and its balance with emission effects. Here, using source fingerprinting techniques, we isolated the autochthonous organic carbon (OCAuto) burial, which represents the intrinsic carbon sequestration of lakes. We found that OCAuto burial accounted for only 53.23% of total lake carbon emissions in the 2020s, leaving China's lakes as carbon sources (-0.83 teragrams of carbon per year). Regionally, lakes on the Qinghai-Tibet and Yunnan-Guizhou Plateaus have shifted to carbon sinks, whereas lakes in the eastern and northeastern regions remain major carbon sources. Scenario projections indicated that restoring China's lakes to macrophyte-dominated states under the Shared Socioeconomic Pathway SSP2-4.5 scenario could transition them into stable carbon sinks before OCAuto burial peaks around 2070. To facilitate this transition, we proposed a lake classification-and-management framework based on carbon sink potential and emission risks to guide carbon sequestration and climate mitigation efforts.