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

University essay from Göteborgs universitet/Institutionen för geovetenskaper

Abstract: Active AS soil has several negative impacts on the environment due to their ability to severely decreasepH-values and mobilize metals bound in the soil. The negative impacts can especially be seen in aquaticenvironments that drains an active AS soil. Active AS soil creates difficulties to reach the environmentalgoals that were set by the Swedish Parliament in 1999. Investigations of the distribution of AS soil inSweden have chiefly been done along the northern coast, Västerbotten, and Norrbotten, but discoverieshave also been done in Mälardalen and Skåne. During a construction work in Falkenberg 2019, water pumpscorroded and the presence of yellowish drainage water with low pH-values and high sulphate concentrationsled to the conclusion that AS soil exists in the area. The focus of this project was to determine thedistribution and existence of AS soil in Falkenberg, on the west coast of Sweden, to shed light on theirformational environment, and to evaluate the suitability of ERT methods as an identification tool for thesesoils on the Swedish west coast. The project was carried out from September 2019 to June 2020 as a masterthesis at the University of Gothenburg in collaboration with SGU. Soil sampling was done during theautumn of 2019 with an extendible Edelman auger. Soil sampling was carried out in areas where earliersoil-type mapping showed occurrence of organic-rich sediments. The soil samples were collected foroxidation and further laboratory analyses, including metal and S analyses at an accredited laboratory. Afterthe oxidation of the soil samples, it was concluded that both active and potential AS soil exists inFalkenberg. Four sites were classified as active AS soil sites and one was classified as a potential AS soilsite. This is the first discovered active AS soil outside of the Baltic Basin in Sweden. All the observationsof AS soil sites were done below 13 m.a.s.l., in clay gyttja, gyttja clay, and sand. When the location of thesesites was established, ERT measurements were done at one of the sites, H19001, during November 2019and February 2020. The results showed that differentiation of the AS soil from surrounding sediments waspossible at this site. The formation of the AS soil on the west coast of Sweden differs from that along theSwedish north coast and is thought to have taken place in shallow protected lagoons and bays during Tapestransgression.

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