What happens to dissolved oxygen levels when acid rain lowers pond pH?

• A. They increase
• B. They remain unchanged
• C. They decrease
• D. They vary depending on temperature

Answer: (C)

When acid rain lowers the pH of a pond, the levels of dissolved oxygen typically decrease. This phenomenon occurs because a lower pH can negatively impact aquatic life, particularly organisms like fish and invertebrates that rely on oxygen in the water.

As the pH drops, it can lead to the leaching of toxic metals such as aluminum from the soil into the water. These metals can be harmful to aquatic organisms, reducing their populations and, consequently, the overall respiration and aeration processes within the ecosystem. Healthy aquatic ecosystems depend on a balanced pH to maintain populations of organisms that contribute to oxygen levels through processes like photosynthesis.

Additionally, lower pH levels can decrease the solubility of oxygen in water. This is because the chemical processes associated with lower pH can alter the environment in which aquatic plants and phytoplankton, which produce oxygen, function effectively. Therefore, lower pH due to acid rain ultimately leads to a reduction in the overall dissolved oxygen levels in the pond.