Carbonate constants for estuarine waters

Abstract

Intensive studies have been made on the carbonate system in seawater. The thermodynamic constants needed to examine the components of the carbonate system have been developed by several authors. The thermodynamic constants for the dissociation of carbonic acid in seawater have been determined on different pH scales. The two most popular pH scales are the total scale: [H⁺]_T = [H⁺]_F{1 + [SO₄^2–]_T/K_HSO4}) and the seawater scale: [H⁺]_SWS = [H⁺]_F {1 + β_HSO4[SO₄^2–]_T/K_HSO4 + β_HF[F^–]_T/K_HF}, where the brackets denote concentrations and the subscripts F and T are for free and total concentrations. The values of K_HSO4 and K_HF are the dissociation constants for HSO₄^– and HF:

As long as the same pH scale and constants for seawater are used, one can evaluate the components of the carbonate system in seawater. Unfortunately, not all the measured and fitted constants have been made for dilute seawater, and thus cannot be used in estuarine waters. In this paper, the measured constants from S = 1 to 50 and t = 0 to 50°C have been determined on the total, seawater and free scale (pH_F = –log[H⁺]_F). These stoichiometric constants can now be used to examine the carbonate system in most estuarine waters.