The exact numerical calculation for the emission of lighter when CO2 = 5.4‰ alters into δ13C = 3.1‰ in inflowing river waters is not known. However, it is possible to calculate the approximate amount of lighter CO2 emitted by applying the Rayleigh fractionation equation. This equation states that the fractionation factor (α) can be calculated as the difference between the δ13C of the two reservoirs (in this case, 5.4‰ and 3.1‰) divided by the difference between the two CO2 concentrations (in this case, 5.4 and 0). Therefore, α = (5.4‰ - 3.1‰)/(5.4 - 0) = 0.567. Using this fractionation factor, the approximate amount of lighter CO2 emitted can be calculated by multiplying the fractionation factor by the difference in the two CO2 concentrations (5.4 - 0). Therefore, the approximate amount of lighter CO2 emitted is 3.1.

Thank you Peter Donkor