Alkalinity

The total alkalinity of a water is the sum of the bases that are titratable with strong acid:

TA = [HCO₃] + 2[CO₃] + [B(OH)₄] + [OH] + [HPO4] + 2[PO₄] + [SiO(OH)₃] + [HS] + 2[S] + [NH₃] – [H] – [HSO₄] – [HF] – [H₃PO₄]^[1]

In seawater alkalinity is roughly equal to the carbonate alkalinity plus borate:

TA = [HCO₃] + 2[CO₃] + [H₂BO₃] ,

In most natural freshwaters total alkalinity is roughly equal to the carbonate alkalinity [2] e.g.:

mHCO₃^– + 2mCO₃^2-

Bicarbonate (HCO₃^–) and carbonate (CO₃^2-) ions are derived from weathering reactions. The hydrolysis of bicarbonate and carbonate helps to buffer (or minimise) pH changes caused by photosynthesis.

1. Lewis, E., and D. W. R. Wallace. 1998. Program Developed for CO₂ System Calculations. ORNL/CDIAC-105. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee.
2. Drever, J.I. 1982. The Geochemistry of Natural Waters, Prentice-Hall, Inc., Englewoods Cliffs, N.J., pp. 388.