ABSTRACT
The behaviour of sedimentary Pb, Ni, Cu, Zn, Fe and Mn in a natural wetland (central Sweden) impacted by acid mine drainage was studied to determine the potential for long-term retention of these metals in the sediments. Partial abundances of metals in peat sediments were determined by a sequential extraction procedure giving five fractions potentially sensitive to changes in environmental conditions. Sampling design was carried out using landscape geochemical and geographic information : y tem techniques. Geochemical abundances, geochemical gradients and geochemical flow patterns were analysed and modelled and the wetland-acid mine drainage interface was interpreted as a landscape geochemical barrier. Geochemical data interpretation and modelling was carried out using the robust techniques of Exploratory Data Analysis to treat multimodal data populations and accommodate information inherent in outlying values. The interpretation of results was enhanced by Multivariate Statistical Analysis. Results show that Pb, Cu and Zn are efficiently retained in stable metal-organo-complexes, but Mn and Ni remain mobile or bound as labile outer-sphere complexes in the reducing environment. Fe migrates with groundwater and diffuses upwards along concentration gradients and precipitates in top layers of peat sediments as amorphous iron oxides. Micro-environments are important in sulphate reduction and sulphide formation in the peat sediments. Under the acidic conditions encountered in the studied mire only copper sulphide may precipitate.
