Acid rain is caused by sulfur dioxide and nitrogen oxides forming acids in the atmosphere. Which statement best describes a documented environmental effect of acid rain?

• A. It lowers lake pH but does not affect soils or vegetation.
• B. It lowers lake pH, mobilizes toxic metals, and damages soils and tree roots.
• C. It is formed when rainwater mixes with methane and has no ecological impact.
• D. It only affects urban air quality and not aquatic systems.

Answer: (B)

Acid rain changes the chemistry of ecosystems by acidifying water and soil, which then affects living organisms and plant growth. This environmental effect includes lowering the pH of lakes and streams, releasing and mobilizing toxic metals like aluminum from soils, and damaging soils and tree roots, which disrupts nutrient uptake and overall forest health.

That makes the statement describing a lake acidification, metal mobilization, and damage to soils and roots the best choice. When rain is acidic, lakes become warmer or more extreme in pH swings, harming fish and aquatic life; in soils, acid deposition leaches away essential base nutrients, lowers pH, and weakens roots, reducing trees’ ability to absorb water and nutrients. The involvement of metal release, especially aluminum, explains additional toxicity to aquatic systems and plants. And acid rain is not formed by rainwater mixing with methane; it results from sulfur dioxide and nitrogen oxides forming sulfuric and nitric acids in the atmosphere, which then fall as acid precipitation. The other options misstate the scope or cause, claiming no soil or vegetation impact, no ecological effect, or only urban air quality effects, which contradicts well-documented ecological consequences.