What does alkalinity measure in water?

Alkalinity is a measure of the water's capacity to resist changes in pH, particularly its ability to neutralize acids. This is primarily due to the presence of bicarbonates, carbonates, and hydroxides in the water. When an acid is introduced to water, alkalinity indicates how much acid can be added before the pH starts to drop significantly. Therefore, this ability to neutralize acid is crucial in aquatic systems as it helps maintain a stable pH, which is essential for the survival of aquatic life and the effectiveness of various water treatment processes.

In contrast, measuring the concentration of dissolved oxygen pertains to the amount of oxygen available in water, which is vital for aerobic organisms, but unrelated to alkalinity. Similarly, the presence of heavy metals is about identifying specific contaminants and pollution levels in water, while total suspended solids refers to particles suspended in water that can affect water clarity and quality but do not relate to the water's acid-neutralizing capacity. Thus, the correct answer emphasizes the role of alkalinity in maintaining chemical balance in water by measuring its buffering capacity against acids.