Which chemical property is significantly impacted by the excess presence of CO2 in water systems?

The excess presence of carbon dioxide (CO2) in water systems primarily affects alkalinity due to its role in the formation of carbonic acid when it dissolves in water. This carbonic acid can alter the pH balance of the water, leading to changes in alkalinity levels. When CO2 is present in higher concentrations, it can increase the concentration of bicarbonate (HCO3-) and carbonate (CO3^2-), essential components that contribute to alkalinity.

Alkalinity, in turn, is crucial because it helps buffer against rapid changes in pH, which are vital for maintaining a stable aquatic environment for organisms. Increased CO2 can lead to decreased pH (more acidic conditions), which can have significant implications for aquatic life and water quality. This relationship demonstrates the critical importance of monitoring carbon dioxide levels to manage the alkalinity of water systems effectively.