The first documented and characterized Norwegian acid sulfate soils

Abstract

Acid sulfate soils (ASS) containing hypersulfidic material (pH >4) can, when drained, transform to ASS with a thionic horizon (pH <4), which can cause environmental effects due to the formation of sulfuric acid and the consequent mobilization and leaching of metals and acid into waterways, as well as cause geotechnical problems. Yet, the occurrence of ASS has till now not been a topic of research in Norway. The present pilot study was carried out on an area along the northern coast of Norway. Thirty‐nine localities were sampled and analysed near Alta. Of these, six were classified as ASS with either hypersulfidic or parahypersulfidic material. ASS is not as widespread as within the Baltic Sea area, but the analyses document the occurrence of ASS with hypersulfidic material with high acidifying potential in certain areas if oxidized. This pilot study shows that ASS occurs in specific areas. Three localities with documented ASS were studied in greater detail. Here, sections were excavated and analysed to help with the understanding of the geological context of these occurrences. In this way, the geological prerequisites considered of importance of soils with ASS with hypersulfidic material are outlined. The prerequisites for ASS occurrence that evolved during this study include young, marine, fine‐grained deposits and a low relief environment subjected to episodic sedimentation but otherwise calm water and little water exchange. The results are a starting point for further studies of ASS occurrences along the Norwegian coast.