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# Table 1 Equations used to calculate surface water pCO2 concentrations and CO2 flux rates

Parameter Units Equation Reference Equation
Dissolved free CO2 (CO2(aq)) mol m−3 $$\left[{\mathrm{CO}}_{2\left(\mathrm{aq}\right)}\right]=\frac{\mathrm{DIC}}{12.01}\times \left[7.0\mathrm{x}{10}^6\times \exp \left(-2.414\times \mathrm{pH}\right)\right]$$ (Wetzel and Likens 2000) 1
Surface water pCO2 atm $${\mathrm{pCO}}_2=\frac{\left[{\mathrm{CO}}_{2\left(\mathrm{aq}\right)}\right]}{K_{\mathrm{H}}}$$ (Gu et al. 2008) 2
CO2 dissolution constant (K H) mol m−3 atm−1 K H = 0.0279T 2 − 2.3895T + 75.819 (Gu et al. 2008) 3
CO2 (CO2(atm)) at the top of the stagnant layer mol m−3 [CO2(atm)] = K H × pCO2(atm) (Gu et al. 2011) 4
CO2flux (F CO2) mol m−2 s−1 $${F}_{{\mathrm{CO}}_2}=\left(\left[{\mathrm{CO}}_{2\left(\mathrm{atm}\right)}\right]-\left[{\mathrm{CO}}_{2\left(\mathrm{aq}\right)}\right]\right)\times \frac{D_{{\mathrm{CO}}_2}}{z}$$ (Gu et al. 2011) 5
CO2 diffusion coefficient (D CO2) m−2 s−1 $${D}_{{\mathrm{CO}}_2}=\frac{\left(-12.2048+0.04752T\right)}{10^9}$$ (Akgerman and Gainer 1972) 6
Surface boundary layer thickness (z) m $$z=\frac{10^{\left(2.56-0.133\;W\right)}}{10^6}$$ (Kling et al. 1992) 7
1. DIC dissolved inorganic carbon, K H Henry’s Law CO2 dissolution constant, T temperature (°C)