Total Alkalinity
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 (CO3) and bicarbonates (HCO3) 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, therefore less stable for aquatic life. Water with higher alkalinity usually has a higher pH. Brackish water or seawater typically has alkalinity of 100 to 125 mg/L.
In areas with no industrial impacts, total hardness and total alkalinity values tend to be very similar.
Waterbodies with little to no alkalinity have less capacity to neutralize acids and because of this, pH can drop below the optimal range for aquatic life (between 6.5 and 8.5), acidifying the water. Changes in pH increase toxicity of certain chemicals, cause harm, stress, and death to fish and other aquatic life.
High alkalinity may indicate runoff from lawns where owners apply limestone to raise the soil’s pH and improve lawn growth. Excessive limestone reaching streams may greatly increase water pH, and reach dangerous levels for aquatic life. For most aquatic life, the optimal alkalinity range is considered to be between 100 and 250 milligrams per liter (mg/L) of calcium carbonate (CaCO3), which provides a stable pH environment by acting as a buffer against sudden changes in acidity.