Carbonate alkalinity

Carbonate Alkalinity is a measure of the amount of carbonate and bicarbonate anions in solution. Carbonate and bicarbonate anions contribute to alkalinity due to their basic nature, hence their ability to neutralize acid. Mathematically, the carbonate anion concentration is counted twice due to its abiliity to neutralize two protons, while bicarbonate is counted once as it can neutralize one proton. Carbonate alkalinity is often the major component of a natural solution's total alkalinity. It is an important factor in understanding large scale environmental interactions based on simple pH and carbon dioxide measurements.

$CT\; (mEq/L)\; =\; [HCO3-]\; +\; 2*\; [CO3-2]$

Alkalinity is commonly expressed as mg/L as CaCO3 because CaCO3 has an equivalent weight of 50.

For water with a pH below 8.5, the CO3-2 will be less than 1% of the [HCO3-]