What environmental risks occur when acid sulfate soils are drained?

• A. Drainage increases crop yield without harm
• B. Drainage oxidizes iron sulfides to sulfuric acid, releasing acidity and metals harming water and biota
• C. Soils with high lime content
• D. There is no risk in draining

Answer: (B)

Acid sulfate soils sit in a reduced, waterlogged state, so the sulfide minerals (like pyrite) are stable. When these soils are drained, air enters and the sulfides oxidize, producing sulfuric acid. That creates acidity in the soil and in drainage water and releases metals trapped in the minerals. The result is acidic water with dissolved metals that can harm aquatic life, degrade water quality, and even corrode infrastructure. Crops may suffer from the acidity and metal toxicity, rather than yielding more. So drainage without proper management leads to environmental damage, not a safe or beneficial outcome.