Metal species in a Boreal river system affected by acid sulfate soils |
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| Institution: | 1. Department of Biology and Environmental Science, Linnaeus University, SE-391 82 Kalmar, Sweden;2. Department of Soil and Environment, Swedish University of Agricultural Sciences, Box 7014, SE-750 07 Uppsala, Sweden;3. Division of Land and Water Resources Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden;1. Department of Biology and Environmental Science, Linnaeus University, SE 39182, Kalmar, Sweden;2. Geological Survey of Finland (GTK), PO Box 96, FI 02151, Espoo, Finland;3. Åbo Akademi University, Department of Geology and Mineralogy, , FI 20500, Åbo, Finland;4. Southern Cross GeoScience, Southern Cross University, PO Box 157, Lismore, NSW 2480, Australia;5. Department of Earth Sciences, University of Gothenburg, SE 405 30, Gothenburg, Sweden;1. UNSW Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia;2. Centre Européen de Recherche et d''Enseignement des Géosciences de l''Environnement (CEREGE), Aix-Marseille Université, Aix en Provence, France;1. Department of Biology and Environmental Science, Linnaeus University, SE-39182 Kalmar, Sweden;2. Centre for Ecology and Evolution in Microbial Model Systems (EEMiS), Linnaeus University, SE-39182 Kalmar, Sweden;3. Laboratory for Isotope Geology, Swedish Museum of Natural History, P.O. Box 50 007, SE-10405 Stockholm, Sweden;1. Department of Food and Environmental Sciences, P.O. Box 27, Latokartanonkaari 11, Environmental Soil Science, FI-00014 University of Helsinki, Finland;2. Finnish Drainage Foundation, Simonkatu 12 B 25, 00100 Helsinki, Finland |
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| Abstract: | The bioavailability of metals and their potential for environmental pollution depends not simply on total concentrations but on their chemical form. Consequently, knowledge of aqueous metal speciation is essential in investigating potential metal toxicity and mobility. Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of sulfate, organic C (OC) and 18 metals/metalloids were investigated in the extremely acidic Vörå River system in Western Finland, which is strongly affected by acid sulfate (AS) soils. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these acidic waters. The most important finding of this study is that the very large amounts of elements known to be released from AS soils (including Al, Ca, Cd, Co, Cu, Mg, Mn, Na, Ni, Si and U) occur and can prevail mainly in toxic forms throughout acidic river systems; as free ions and/or sulfate-complexes. This has serious effects on the biota and particularly dissolved Al can be expected to have acute effects on fish and other organisms. In the study area, only the relatively forested upstream area (higher pH and contents of OC) had significant amounts of a few bioavailable elements (including Al, Cu, Ni and U) due to complexation with the more abundantly occurring colloidal OC in the upstream area. It is, however, notable that some of the colloidal/particulate metals were most likely associated with metal bearing phyllosilicates eroded from clay soils. Moreover, the mobilisation of Fe and As was small and As was predicted to be associated with Fe oxides, indicating a considerable influence of Fe oxides on the mobilisation/immobilisation processes of As. Elements will ultimately be precipitated in the recipient estuary, where the acidic metal-rich river water will gradually be diluted/neutralised with brackish seawater in the Gulf of Bothnia. According to speciation modelling, such a pH rise may first cause precipitation of Al, Cu and U together with organic matters closest to the river mouth, in line with previous sediment studies from the estuary. |
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