“…Using the equation provided by Morel and Hering (), the total [DIC] at the biofilm surface can be calculated as (considering that the hydration of CO 2 at the biofilm surface is instantaneous, which is the ideal case): H CO2 is the Henry's constant for CO 2 , and has a value of 0.304 mM kpa −1 ; p CO2 is the CO 2 partial pressure in the gas phase, K a1 and K a2 are the dissociation coefficients of carbonic acid and bicarbonate ion, with value of 10 −6.3 and 10 −10.3 , respectively; pH surface is the measured pH value at the biofilm surface (Murphy and Berberoglu, ; Wolf et al, ). Distribution of the total [DIC] at depth x can be acquired from a transformation of mass balance equation: D e,DIC is the effective diffusion coefficient of DICs in biofilm, and was assumed to equal the value of bicarbonate ions, which has a value of 1.18 × 10 −9 m 2 s −1 in pure water (Murphy and Berberoglu, ). DIC speciation at depth x was calculated from the measured pH profiles: …”