Which statement best describes the potential effect of acid rain on soils?

• A. It lowers soil pH but has no effect on metal mobility.
• B. It raises soil pH and reduces metal availability.
• C. It has no impact on soil chemistry.
• D. It lowers soil pH, mobilizes metals, and harms sensitive plants and aquatic life.

Answer: (D)

Acid rain changes soil chemistry by acidifying it and altering how metals behave in the soil. When acidic compounds enter the soil, hydrogen ions push out basic nutrients and lower the soil pH. As pH drops, metals such as aluminum and other potentially toxic metals become more soluble and mobile, meaning they can move through the soil and into plant roots or leach into water systems. This increased metal mobility, combined with the loss of essential nutrients like calcium and magnesium, stresses plants, harms soil organisms, and can harm aquatic life when these effects reach streams and lakes. That combination—lower pH, metals becoming more mobile, and negative effects on plants and aquatic ecosystems—best matches the described impact of acid rain. The other ideas don’t fit because acid rain does lower pH, does increase metal mobility, and does affect soil chemistry and ecosystems; it does not raise pH.