Discharge of potentially toxic elements from acid sulfate soils in western Finland: Conflict between water protection and land use?

Acid sulfate soils (ASS) are commonly found in many coastal areas worldwide and typically develop from artificial draining of sulfidic sediments, which release acidity and metals, causing unfavuorable effects on recipient watercourses. This study estimates the actual amounts of metals and elements carried to the Gulf of Bothnia and the Baltic Sea by stream water yearly. The combined load from the many small streams and ditches was found to be proportionally high related to the size of their catchment, emphasizing the importance of including numerous small streams in the understanding of pollution in fresh water and marine environments. This study shows that Cd concentrations in the majority of the studied rivers exceed the Environmental Quality Standard set by the European Union (EU). This causes lowered ecological and chemical status according to the European classification system. Many potentially toxic elements discharge yearly to the Baltic Sea in large quantities from the study area: Thousands of tons of Al and Mn, tens of tons of Co, Cu and Ni, and hundreds of kg of Cd. A challenge for the estimation was irregular, or even missing, data for many rivers, which highlights careful planning of monitoring programs. While the current land use on ASS requires efficient drainage, the national and European strategies and legislation aim towards improved status in water bodies and forbid pollution of the environment. Therefore, the land use and water protection policy conflict.