Overview Data Input Data Output DIC Charge Balance Physico-Chem Params Reactions Redox Mineral Phases

Carbonate System -- Main Parameters

All relevant information about the carbonate system (buffer capacities, alkalinity, water hardness) is displayed in the right screenshot.¹ (Here we use the example water gw.sol.)

Buffer Capacities

In the upper part of the panel, four types of buffer capacities (in meq/L) are listed:

ANC to pH 4.3	(≈ M alkalinity)
ANC to pH 8.2	(≈ P alkalinity)
BNC to pH 4.3	(≈ –M alkalinity)
BNC to pH 8.2	(≈ –P alkalinity)

For each type of buffer capacity two values are displayed:

• first value – refers to the case when there is no precipitation or dissolution of minerals

• second value (in brackets) – refers to the case when minerals precipitate or dissolve²

Alkalinity

Two types of alkalinity are shown (in meq/L):

• M alkalinity  (total alkalinity)
• P alkalinity

Both quantities are interrelated via the total dissolved inorganic carbon (DIC):

(1)	DIC  =  M – P

Water Hardness

• TH	total hardness	in meq/L CaCO3
• CH	carbonate hardness (temporary hardness)	in meq/L CaCO3
• NCH	non-carbonate hardness (permanent hardness)	in meq/L CaCO3

Based on the calculated TH value the water is classified into four categories:

• soft
• moderately hard
• hard
• very hard

Carbonate Species

The total dissolved inorganic carbon (DIC) is decomposed into four parts:

•   CO2 = CO2(aq) + H2CO3	composite carbonic acid H2CO3*
•   HCO3-	bicarbonate (hydrogen carbonate)
•   CO3-2	carbonate
•   carbonate complexes	CaCO3(aq) + CaHCO3+ + MgCO3(aq) + …

Thus, for the molar concentrations we have:³

(2)	DIC  =  [CO2] + [HCO3-] + [CO3-2] + carbonate complexes

CO₂ Partial Pressure

pCO2 is a measure of the amount of CO₂(g) dissolved in water – more details are here.

Remarks & Footnotes