What causes the pH of coastal waterways to change?
• The pH of coastal waters responds to changes in: (i) dissolved carbon dioxide concentrations; (ii) alkalinity; (iii) hydrogen ion concentrations; and (iv) in a small way to temperature. The concentration of carbon dioxide in solution is proportional to the partial pressure of the gas above the solution (i.e. Henry’s Law). Therefore an increase in CO2 in the atmosphere (due to the greenhouse effect) directly leads to an increase in the amount of CO2 absorbed by oceans. This is called ocean acidification, and is a very topical issue. • The magnitude of pH change (due to the above factors) varies with salinity because various ions are involved in acid-base reactions, and because the concentration of salt influences various equilibrium constants [11]. In natural waters, pH increases with salinity until calcium carbonate (CaCO3) saturation is reached (see Figure 2). When CaCO3 (calcite or aragonite) precipitates, the carbonate-alkalinity of water decreases. This causes a reduction in the
