Alkalinity
Alkalinity is a measure of all the substances in water that can resist a change in pH when acid is added to the water. In other words, alkalinity describes how well a water recovers from an "acidic" punch.

Alkalinity is typically expressed in mg/L of calcium carbonate (CaCO₃) because calcium carbonate is a good acid neutralizer. Water with low alkalinity has a low capacity to neutralize or "buffer" incoming acids and is, therefore, very susceptible to acidic pollution. In contrast, water with greater alkalinity, or buffering capacity, will have the ability to neutralize more of the incoming acidity and, therefore, resist rapid changes in pH. Sufficient alkalinity in water protects aquatic life against rapid changes in pH and makes water less vulnerable to acid rain.

Alkalinity in the Red River
Alkalinity of 100-200 mg/L will sufficiently stabilize the pH in a stream (colored band on graph). As shown on the graph below, the waters of the Red River in the Fargo-Moorhead (FM) area average 216 mg/L, a rather high alkalinity. This alkalinity is maintained because the Red River is surrounded by alkaline soils and geologic deposits (soils and geologic deposits rich in dolomite and limestone that contain carbonate). Although high alkalinity is often associated with hard water and high dissolved solids, characteristics that may adversely affect the water's use and taste, there are no negative health effects from alkalinity.

Graph of alkalinity (mg/L) for the Red River in the FM metro area for the period
January 2001 to January 2003 in relation to the level of alkalinity
(100 to 200 mg/L shown in green) needed to stabilize pH.