| Summary: | Lakes and other inland waters contribute significantly to regional and global carbon budgets. Emissions from lakes are often computed as the product of a gas transfer coefficient, k
600
, and the difference in concentration across the diffusive boundary layer at the air–water interface. Eddy covariance (EC) techniques are increasingly being used in lacustrine gas flux studies and tend to report higher values for derived k
600
than other approaches. Using results from an EC study of a small, boreal lake, we modelled k
600
using a boundary-layer approach that included wind shear and cooling. During stratification, fluxes estimated by EC occasionally were higher than those obtained by our models. The high fluxes co-occurred with winds strong enough to induce deflections of the thermocline. We attribute the higher measured fluxes to upwelling-induced spatial variability in surface concentrations of CO2 within the EC footprint. We modelled the increased gas concentrations due to the upwelling and corrected our k
600
values using these higher CO2 concentrations. This approach led to greater congruence between measured and modelled k values during the stratified period. k
600
has a well-resolved and ~cubic relationship with wind speed when the water column is unstratified and the dissolved gases well mixed. During stratification and using the corrected k
600
, the same pattern is evident at higher winds, but k
600
has a median value of ~7 cm h−1 when winds are less than 6 m s−1, similar to observations in recent oceanographic studies. Our models for k
600
provide estimates of gas evasion at least 200% higher than earlier wind-based models. Our improved k
600
estimates emphasize the need for integrating within lake physics into models of greenhouse gas evasion.
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