Acid sulphate soil in Falkenberg on the west coast of Sweden - The first discovery of active acid sulphate soil outside the Baltic Basin

Abstract

Active AS soil has several negative impacts on the environment due to their ability to severely decrease pH-values and mobilize metals bound in the soil. The negative impacts can especially be seen in aquatic environments that drains an active AS soil. Active AS soil creates difficulties to reach the environmental goals that were set by the Swedish Parliament in 1999. Investigations of the distribution of AS soil in Sweden have chiefly been done along the northern coast, Västerbotten, and Norrbotten, but discoveries have also been done in Mälardalen and Skåne. During a construction work in Falkenberg 2019, water pumps corroded and the presence of yellowish drainage water with low pH-values and high sulphate concentrations led to the conclusion that AS soil exists in the area. The focus of this project was to determine the distribution and existence of AS soil in Falkenberg, on the west coast of Sweden, to shed light on their formational environment, and to evaluate the suitability of ERT methods as an identification tool for these soils on the Swedish west coast. The project was carried out from September 2019 to June 2020 as a master thesis at the University of Gothenburg in collaboration with SGU. Soil sampling was done during the autumn of 2019 with an extendible Edelman auger. Soil sampling was carried out in areas where earlier soil-type mapping showed occurrence of organic-rich sediments. The soil samples were collected for oxidation and further laboratory analyses, including metal and S analyses at an accredited laboratory. After the oxidation of the soil samples, it was concluded that both active and potential AS soil exists in Falkenberg. Four sites were classified as active AS soil sites and one was classified as a potential AS soil site. This is the first discovered active AS soil outside of the Baltic Basin in Sweden. All the observations of AS soil sites were done below 13 m.a.s.l., in clay gyttja, gyttja clay, and sand. When the location of these sites was established, ERT measurements were done at one of the sites, H19001, during November 2019 and February 2020. The results showed that differentiation of the AS soil from surrounding sediments was possible at this site. The formation of the AS soil on the west coast of Sweden differs from that along the Swedish north coast and is thought to have taken place in shallow protected lagoons and bays during Tapes transgression.