Predictions suggest that atmospheric concentrations of CO2 will continue to increase throughout the 21st century, although there is a lot of uncertainty about CO2 trajectories because they depend on the actions of nations around the world, and there is a paucity of information on future CO2 emissions (Najjar et al. 2010). Surface-water CO2 changes will lead to a decrease in pH and carbonate-ion concentrations (Orr et al. 2005; Najjar et al. 2010).ResearchonpHchangeshasfocussedonmarinesystems, although, recently, Mosley et al. (2010) developed an estuarineequilibrium model using the composition of the river and seawater end members to model pH across salinities (see also Hunter 2007). Using this model, pH initially declined at low salinities (,2), then increased rapidly, before stabilising at higher salinities (.15) (Mosley et al. 2010).