Acid precipitation.

Burning fossil fuels also releases excess sulfur into the atmosphere, forming sulfuric acid.

The acid can fall back to earth as acid precipitation, lowering the pH in ecosystems.

Acidified soils damage plants by interfering with cation exchange.

Regulations such as the Air Pollution Control Act of 1955 and the Clean Air Act of 1963 slowed the acidification of waters, as measured at the Hubbard Brook Experimental Forest.