Dominant environmental influencing factors of carbon dioxide fluxes in lakes and reservoirs at different time scales

Lakes play a crucial role in the carbon exchange of inland waters. However, determining the factors influencing carbon dioxide fluxes (FCO2) from lakes remains challenging. Here, we synthesize 332 months of eddy covariance measurements from 19 lakes and 8 reservoirs (collectively referred to as lakes) to identify the dominant environmental factors of FCO2 across multiple timescales and to explore the carbon dioxide (CO2) exchange mechanisms among different lake types. We found that increasing lake pH enhances the likelihood of the system acting as a carbon sink. The dominant factors influencing FCO2 differ markedly across timescales: radiation-related factors at the diel scale, energy exchange-related factors at the multi-day scale, and temperature-related factors at the seasonal scale. Relative mutual information results further reveal that the lags of these dominant factors vary among lake types. For the dominant factor on the diel scale, the lags of shortwave radiation incoming in acidic, neutral, and alkaline lakes are −0.3±0.5 days, 0.4±0.9 days, and 0.2±0.7 days, respectively. The multi-day scale dominant factor, sensible heat, also has the shortest lags in acidic lakes. Seasonally, the lags of temperatures are more variable, indicating the influence of dominant factors on FCO2 and the lagged relationships are more diverse and complex on longer time scales. Our study highlights the importance of multi-site synthesis when extrapolating and generalizing scales across lake types. Understanding the drivers and mechanisms for lake FCO2 can help improve future simulations and the accurate estimation of lake carbon budgets.