What happens in the carbonate buffering system when acid is added?

In the carbonate buffering system, adding acid leads to a chemical reaction where carbonate ions (CO3^2-) combine with hydrogen ions (H+) introduced by the acid. This reaction helps to mitigate changes in pH, stabilizing the aqueous environment. The result is that the buffering system absorbs excess hydrogen ions, forming bicarbonate ions (HCO3^-). This process prevents drastic fluctuations in pH, thus maintaining a balanced aquatic ecosystem.

The other options do not accurately represent the effects of adding acid to the carbonate buffering system. For instance, a drastic increase in pH would be contrary to the buffering action; instead, the pH remains relatively stable. The assertion about pesticides becoming more concentrated does not relate directly to the buffering system's response but rather to other environmental factors. Lastly, salinity levels would not inherently rise because of added acid; salinity is more influenced by the concentration of salts in the water, not directly by acidity.