What does alkalinity measure in water?

Alkalinity measures the capacity of water to resist changes in pH, thereby contributing to its stability. It refers to the presence of bicarbonate, carbonate, and occasionally hydroxide ions, which act as buffers in the water. When acids are introduced into a water body, these buffering agents react with the acids, helping to maintain a stable pH level. This quality is crucial for aquatic ecosystems, as many organisms thrive within specific pH ranges, and significant fluctuations can be detrimental. A higher alkalinity signifies a greater ability to buffer against pH changes, thus supporting a stable environment for aquatic life.

The other choices do not accurately define alkalinity. Temperature resistance relates to physical properties of water rather than chemical stability. The presence of minerals is more about hard water or mineral content rather than its buffering capacity. Organic matter impacts water quality but does not serve as a measure of alkalinity.