Characterization of atmosphere–water exchange processes of CO2 in estuaries using dynamic simulation

CO2 is one of the so-called “greenhouse effect” gases; therefore, its rates of water–atmosphere exchange are very relevant for studies of climate change. Coastal zones (which include estuarine systems) are of special interest in relation to the global carbon cycle. Thus, an estuary simulator, which operates in a dynamic mixing regime, is specifically applied in an initial study of the estuarine dynamic of inorganic carbon, focusing basically on the influence of salinity and pH on the water–atmosphere fluxes of CO2 in these zones. The simulation has been performed under two assumptions: (i) considering that the system is subjected to a stationary gradient of salinity and (ii) taking into account the effect of the tides, owing to the daily oscillations introduced by this phenomenon in the process of CO2 transfer between the water and the atmosphere. After analysing the results, it has been observed that a potential source of error exists when choosing the coefficients of gas exchange (k) for CO2 studies. Nevertheless, the evolution of CO2 fluxes along the salinity and pH gradients achieved shows the same trends with those observed in a wide variety of real estuaries described in the related literature.