Step 4: Carbonate System and Calcite Saturation

Buffer Capacities & Alkalinity

aqion: output of carbonate-system data

All relevant information about the carbonate system, buffer capacities, alkalinity, and water hardness are summarized in the right screenshot.¹

The upper part shows the calculated buffer capacities (ANC and BNC).

Additional information shown in this panel are:

M alkalinity in meq/L (i.e. total alkalinity)
P alkalinity in meq/L
TH – total hardness
CH – carbonate hardness
water type (soft or hard water)
carbonat speciation (HCO₃^-, CO₃^-2, CO₂)
CO₂ partial pressure

For more information see here.

Calcite Saturation

aqion. output of calcite-saturation data

This screenshot refers to the calcite-carbonate system:²

• saturation pH at given evaluation temperature (which may or may not differ from sampling temperature)

• Langelier Saturation Index (LSI)

• state of water: corrosive, scale-forming, or in equilibrium with calcite

• saturation pH after CO2 exchange

• saturation pH according to Strohecker/Langelier

• saturation index (SI) of calcite

• Calcium Carbonate Precipitation Potential (CCPP)

• amount of precipitated or dissolved calcite in mg/L

In addition, the CO₂ (carbonic acid) is split into “free” CO₂ and “bound” CO₂. This allows to quantify the

CO₂ in excess (aggressive CO₂) or
CO₂ deficit

In the given example the water tends to be scale forming (i.e. calcite precipitates). The corresponding saturation index as well as the calcium carbonate precipitation potential are both positive (non-negative).

Footnotes

This panel is the left part of a larger window shown here. ↩
This panel is the right part of a larger window shown here. ↩

[last modified: 2020-12-31]