Modelling of pH and inorganic carbon speciation in estuaries using the composition of the river and seawater end members

Abstract

An equilibrium model based on the CO 2 system was developed to model pH throughout the estuarine salinity range using the composition of the river and seawater end members. In order to validate the model, a spectrophotometric method was used to measure pH in an estuary and laboratory mixing experiments. The model successfully represented the measured pH values (±0.1 pH units) for three different river water end member compositions. The pH decreased at low salinities ( S ≈ 0–2), increased at intermediate salinities ( S ≈ 2–15), and then stabilised for higher salinity values. Changes in the inorganic carbon speciation in the low salinity region of estuaries result in assimilation of river borne CO 2(aq).