Acid sulphate soils and its influence on metal concentrations in adjacent water bodies. - A case study from Halland, SW Sweden
Sammanfattning: Acid sulphate soils have been referred to as being among the most harmful soils in the worlddue to their ability to severely decrease the pH of the water, consequently enabling an increasedmetal load to recipient water streams, lakes, groundwater reservoirs and estuaries. The presenceof acid sulphate soils has triggered several fish kill episodes in northern Scandinavia and thesoils are today threatening many of the national environmental goals of Sweden. Theirwidespread coverage in northern Sweden and western Finland have endorsed these regions tobe the focal point for previous investigations. However, in early 2019, acid sulphate soils werediscovered in Halland, SW Sweden and this study therefore aimed to investigate the impactfrom these non-investigated soils on the surface water chemistry of an affected area. This wasconducted through in situ surface water sampling from two areas, in order to cover both smallerditches (area 1) and a larger canal (area 2), located adjacent to a confirmed acid sulphate soil.Sampling was conducted during three separate occasions; autumn, winter and spring with thepurpose of investigating differences in discharge depending on season. Water pH and electricconductivity was determined in situ, and the total metal compositions of Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, Pb, V and Zn was analysed with an ICP-MS instrument. Additionally,groundwater data was collected to determine potential impact on the drinking water of theregion. The results provide strong indications of leakage from the acid sulphate soils into thesurface water, visible through elevated metal concentrations along with pH values between 3.8and 6.6. Additionally, high electric conductivity values were measured in the water (32-129mS/m) implying high SO42- composition in the water. Higher metal concentrations and lowerpH values were measured in area 1 compared to area 2, hence assumed to be more influencedby the adjacent sulphuric soil layer. The metal concentrations in the water decreased fromautumn to spring, likely reflecting the high temperatures and prolonged precipitation in Halland2019/2020, further implying the importance of considering climatic parameters wheninvestigating acid sulphate soil leaching. No indications of contaminated groundwater wereseen in the results; however, no definite conclusions could be drawn due to limitations in thedataset. The study site was further compared to other sites in Sweden and Finland, whereindications of slightly lower discharge were seen in Halland.
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