Representative data for the diurnal cycle of observed fCO₂ in the water and estimated fCO₂ in the water on the assumption that the NEP was zero (fCO₂ without NEP) at the boreal site in the summer of 2010 (a). Parameters related to fCO₂ in the water, such as DIC (DIC_SAV and DIC_basis in Eqn 4) (b), water temperature, and salinity (c) are also presented. Shading indicates the period of darkness. The peaks of fCO₂ in the water at about 10 and 30 h were caused by an intermittently high fCO₂ water inflow from the river, as indicated by the low salinity and moderate DIC at the time.