Acid sulphate soils

Acid sulphate soils are layers of soil with a high sulphur and iron content found on low-lying coasts, especially along the Gulf of Bothnia. Iron and other metals may dissolve into water from acidic sulphate soils if the groundwater surface fluctuates or other changes occur in the hydrological conditions. This causes acidification of the groundwater. If, for example, a long dry period is followed by heavy rain that leaches sulphate soils, even surface waters can become temporarily acidified.