Environmental applications of biogeochemical data from Geological Survey of Sweden

Sammanfattning: The Geological Survey of Sweden, SGU, has carried out geochemical mapping for several decades. In 1983, two regional mapping programmes were initiated, aiming at a nation wide coverage. While one of the programmes, till geochemical mapping, was focussed mainly on production of regional baseline information for mineral exploration purposes, the second programme was more adapted to environmental issues. This second programme constitutes sampling of living matter (roots of Carex species, Filipendula Ulmaria, and the bryophyte Fontinalis Antipyretica) in minor streams, and is called biogeochemical mapping. Despite more than twenty years of mapping, several aspects of the method and its results still remain unexplored. Furthermore, results from the biogeochemical mapping programme have traditionally been expressed as residuals (contents in ash, contents of iron and manganese, and loss on ignition have been used as independent variables). This residual method however is not used in the Fontinalis antipyretica monitoring method developed by the Swedish Environmental Protection agency (SEPA), thus use of the SGU regional data set as baseline information in a SEPA context is very difficult. Therefore, a transition to dry weight is desirable. This however introduces several problems, e. g. for chromium. Following an introduction to the development and current status of the geochemical mapping programmes, two environmental applications of the biogeochemical dataset have been developed through a combination of statistical and geostatistical methods. In the first, subsets of the biogeochemical database have been created and used in order to determine possible species dependent effects, spatial correlation and influence of main elements like titanium, iron, aluminium, silica, and manganese on chromium. In the second, relations between the chemical composition of samples and areas known (and suspected) to host acid sulphate soils are studied. The species studied vary somewhat regarding metal contents. Such differences are assumed to be related to uptake mechanisms. However, for most elements the differences are much smaller than the spatial variance and the results from the mapping programme can be used without respect to species. Other geochemical databases (till and soil), as well as geological data, have been used in order to examine the geochemical properties of the biogeochemical samples, and factors affecting spatial distribution, e.g. relationships with quaternary deposits. Chromium contents in biogeochemical samples are strongly related to titanium, silica, zirconium and ash content. This correlation is not present in glacial till and other quaternary deposits. Normalisation of chromium by titanium is an efficient tool to separate anthropogenic point source pollution from chromium derived from natural sources. Acid sulphate soils have a strong impact on surface waters, and ecosystems therein. The metal contents of biogeochemical samples in two separate areas where acid sulphate soils occur display similar features asstream water. Of the elements studied, levels of yttrium, nickel, cobalt, zinc, sulphur, (and others) are significantly higher in samples collected in areas with postglacial clays and gyttja containing soils, deposits that are known to comprise acid sulphate soils. The metal content of the biogeochemical samples can be used in order to detect active acid sulphate soils.