What is acid neutralizing capacity (ANC) and how does it affect lakes responding to acid deposition?

What is acid neutralizing capacity (ANC) and how does it affect lakes responding to acid deposition?

• A. ANC measures a water body's ability to neutralize acid; lakes with high ANC resist pH decline, while lakes with low ANC acidify rapidly.
• B. ANC is the amount of calcium in water; higher ANC means more acidification.
• C. ANC refers to buffering in soils only.
• D. ANC is the rate at which lakes respire.

Answer: (A)

Acid neutralizing capacity is the water’s buffering ability to neutralize added acids, mainly provided by carbonate and bicarbonate ions that react with hydrogen ions. When acid deposition adds H+, these buffering species absorb the excess H+ and form carbonic acid, which becomes CO2. This reaction slows or limits the decrease in pH, so lakes with greater buffering capacity resist acidification better. Lakes with high ANC have a substantial reservoir of bases, so the pH stays relatively stable even as acids are added. Lakes with low ANC have little buffering capacity, so each dose of acid pushes the pH downward more quickly, making them more susceptible to acidic conditions that can harm aquatic life and release toxic metals. ANC isn’t just about calcium content; it reflects the overall buffering capacity of the water (primarily from carbonate/bicarbonate) to neutralize acids. Therefore, the more ANC a lake has, the less it will respond to acid deposition with a drop in pH; the less ANC it has, the more rapidly its pH will fall.

Acid neutralizing capacity is the water’s buffering ability to neutralize added acids, mainly provided by carbonate and bicarbonate ions that react with hydrogen ions. When acid deposition adds H+, these buffering species absorb the excess H+ and form carbonic acid, which becomes CO2. This reaction slows or limits the decrease in pH, so lakes with greater buffering capacity resist acidification better. Lakes with high ANC have a substantial reservoir of bases, so the pH stays relatively stable even as acids are added. Lakes with low ANC have little buffering capacity, so each dose of acid pushes the pH downward more quickly, making them more susceptible to acidic conditions that can harm aquatic life and release toxic metals. ANC isn’t just about calcium content; it reflects the overall buffering capacity of the water (primarily from carbonate/bicarbonate) to neutralize acids. Therefore, the more ANC a lake has, the less it will respond to acid deposition with a drop in pH; the less ANC it has, the more rapidly its pH will fall.