How Does Acid Rain Make Lake Waters Acidic?
Acid rain lowers the pH of lake water, making it more acidic, primarily through two mechanisms: direct deposition and leaching.
Acid rain, formed when sulfur dioxide and nitrogen oxides react with water, oxygen, and other chemicals in the atmosphere, falls directly onto lakes. This directly increases the hydrogen ion (H+) concentration in the lake water, lowering its pH. The EPA explains that the increased acidity directly impacts aquatic life. As stated in the New Hampshire Department of Environmental Services fact sheet, acid rain increases the acidity of lake water causing significant changes.
Leaching of Aluminum
Secondly, as acidic rainwater percolates through the soil, it dissolves aluminum from soil clay particles. This aluminum is then carried into streams and lakes, further contributing to their acidity. The Better Planet Education factsheet highlights the release of toxic substances like aluminum due to increased acidity. This leaching process exacerbates the problem beyond the direct impact of acidic precipitation. The Alberta government report mentions the significant number of acidic lakes in eastern Canada resulting from acid deposition.
Consequences of Acidified Lake Water
The increased acidity in lakes has several detrimental effects, including:
- Damage to aquatic life: Many aquatic organisms are sensitive to pH changes and cannot survive in highly acidic waters.
- Mobilization of toxic metals: As mentioned above, acid rain leaches aluminum and other heavy metals from the soil, making them more available and potentially toxic to aquatic life.
- Changes in water chemistry: Acidification alters the chemical balance of lake water, affecting nutrient cycling and the overall health of the ecosystem.
The chronic acidification of runoff from acid deposition, especially in areas with low weathering rates, like those overlying granite, sandstone, and schist, directly contributes to acidification of headwater streams and lake waters (Acid deposition on acid sensitive catchments). This means that geological factors can exacerbate the impact of acid rain. National Geographic also supports this by noting the impact of acid rain on aquatic environments.
