Re-estimating China's lake CO₂ flux considering spatiotemporal variability

The spatiotemporal variability of lake partial carbon dioxide pressure (pCO₂) introduces uncertainty into CO₂ flux estimates at the lake water-air interface. Knowing the variation pattern of pCO₂ is important for obtaining accurate global estimation. Here we examine seasonal and trophic variations in lake pCO₂ based on 13 field campaigns conducted in Chinese lakes from 2017 to 2021. We found significant seasonal fluctuations in pCO₂, with decreasing values as trophic states intensify within the same region. Saline lakes exhibit lower pCO₂ levels than freshwater lakes. These pCO₂ dynamics result in variable areal CO₂ emissions, with lakes exhibiting different trophic states (oligotrophication > mesotrophication > eutrophication) and saline lakes differing from freshwater lakes (-23.1 ± 17.4 vs. 19.3 ± 18.3 mmol m^-2 d^-1). These spatiotemporal pCO₂ variations complicate total CO₂ emission estimations. Using area proportions of lakes with varying trophic states and salinity in China, we estimate China's lake CO₂ flux at 8.07 Tg C yr^-1. In future studies, the importance of accounting for lake salinity, seasonal dynamics, and trophic states must be noticed to enhance the accuracy of large-scale carbon emission estimates from lake ecosystems in the context of climate change.