Neglecting diel dynamics underestimates Global lakes CO2 emissions by almost 20%

Here we synthesize 616 high-frequency diel CO2 flux observations from 158 lakes worldwide to quantify this bias and identify its environmental controls. Nighttime fluxes were, on average, 27% higher than daytime fluxes, with 69% of lakes exhibiting a night-enhanced regime (NER) driven mainly by productive, shallow and low-latitude systems.

Notably, 22% of lakes shifted from daytime CO2 uptake to nighttime emission, indicating potential misclassification of lake source-sink status. A contrasting day-enhanced regime (DER) occurred more frequently in dissolved organic carbon (DOC)-rich and higher-latitude lakes. The strength of diel asymmetry increased with chlorophyll-a (Chl-a) under low-to-moderate productivity but saturated under high trophic conditions.