Alkalinity is a measure of the buffering capacity of water. Higher alkalinity in a body of water provides a “buffer” against changes in pH, making it more stable for aquatic life.
Limestone is a natural source of alkalinity. The chemical name of limestone is calcium carbonate (CaCO3) or magnesium carbonate (MgCO3). When limestone dissolves in water, carbonates and bicarbonates are produced, and alkalinity rises. If a waterbody has low alkalinity, it is susceptible to rapid changes in pH if acids or bases enter the water. Water with higher alkalinity usually has a higher pH.
Alkalinity of natural waters in Alabama comes primarily from carbonates and bicarbonates leached from soil and rocks. Alkalinity values across Alabama range from 10 mg/L or less in parts of the Coastal Plain to 200 mg/L and more in regions with limestone formations and outcrops, such as in the Upper Coosa River Basin, the Black Belt and the Interior Plateau (Limestone County area). Brackish water or seawater typically has alkalinity of 100 to 125 mg/L.