Acid sulfate soils: A challenge for environmental sustainability

Acid sulfate (AS) soils contain sulfidic compounds formed in anaerobic conditions. In aerobic conditions, they will oxidize to sulfuric acid, which commonly lowers the pH to 3 – 4. These soils cover approximately 10,000 km2 in Finland, mainly on the western coast, and over 170,000 km2 globally. Acidity and the metals dissolved from the soil matrix and leached out of the soil are serious threats to aquatic biota. Initially, AS soils were regarded as an exclusively agricultural problem, but since the 1970s nearly all studies of AS soils have been environmentally motivated. Awareness of these soils has also risen in forestry, peat mining, and in engineering projects. Liming and water management are the key methods toward the sustainable use of these soils.