Public defence in environmental science: Alexandra Nyman

In order to receive the Zoom link for the thesis defense, please contact Faculty Administrator Linnéa Larsson: linnea.larsson@lnu.se

Abstract

Acid sulfate soils are some of the most problematic soils on Earth due to their significant release and mobilisation of acidity and metals. In Sweden, these soils have been studied to a lesser extent than in some other countries where they occur as frequently. The aim of this thesis was to determine the geographical distribution and geochemical (and microbiological) features of acid sulfate soils in Sweden.

Field work included visiting 126 sites distributed relatively evenly throughout the coastal plains, with each site located where acid sulfate soils were most likely to have developed. A wide range of geochemical analyses were carried out: analyses of pH in situ and after incubations in the laboratory; loss on ignition; and chemical extractions using water, 1M HCl, aqua regia, and a strong 4-acid digestion followed by ICP analyses. Statistical analyses of the geochemical data included mostly non-parametric tests for univariate and bivariate methods, and compositional data analysis for multivariate methods. Microbiological analyses were carried out by a co-author.

A total of 47% of all the sampled sites were classified as acid sulfate soils, either directly in the field or after laboratory incubations. Acid sulfate soils were identified on all coastal plains, with the highest relative occurrence in the northeast. The southeast coastal plains had a higher relative occurrence than expected and the lowest measured field pH, lowest incubation pH, and the highest S concentrations. A large number of geochemical features were identified and characterized. These included losses of major and trace elements from the sulfuric soil material; physicochemical differences between acid sulfate soils in the north and south; and high water-soluble concentrations of several elements (e.g. Cd, Co, Mn, Ni, and Zn) indicating that these elements are at a large risk of mobilisation and leaching. Furthermore, several chemical elements were retained in the sulfuric soil material (e.g. Fe, As, Cr, Cu, U), most likely due to binding by secondary Fe (III) phases. These retained elements are susceptible to future leaching, for example under remediation scenarios that raise the groundwater table to re-introduce reducing conditions.