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The greatest gas loss from dimictic lakes occur during spring and autumn mixing periods. Thus, we measured daily concentration gradients of carbon gases (CO₂ and CH₄) in mesohumic Lake Pääjärvi during the mixing periods in autumn 2004 and spring 2005 and calculated and compared the fluxes using three different methods: the boundary layer diffusion model (ΔCO₂ and ΔCH₄), floating static chambers (FC), and changes in gas storage. CO₂ fluxes were higher in autumn than in spring, whereas CH₄ fluxes were lower in autumn than in spring. The method based on changes in storage underestimated the fluxes whereas the floating chambers and the boundary layer diffusion models resulted in similar estimates. However, the chambers always yielded somewhat higher fluxes. Total ΔCO₂ flux in autumn was 883 mmol m⁻² and in spring, 666 mmol m⁻², whereas total ΔCH₄ fluxes were 0.60 mmol m⁻² and 0 …