Integrated Modelling of ACID Mine Drainage Impact on a Wetland Stream using Landscape Geochemistry, GIS Technology and Statistical Methods

The attenuation of Cu, Fe, Mn, Ni, Pb and Zn originating from acidic ore mine leachate is studied in a natural wetland stream environment in central Sweden. A sequential chemical extraction procedure is used to investigate fractions that are expected to act as potential sinks of the six metals studied in the stream sediment. Geochemical abundances, geochemical gradients and geochemical flow patterns are analysed and modelled and the stream sediments are interpreted as an oxidising landscape geochemical barrier. Sampling locations and geochemical barriers are identified using landscape geochemical methods and GIS techniques. For data modelling robust statistical methods of Exploratory Data Analysis are used to treat small sample sizes with multi-modal character and outlying values. The spatial variability of metal retention in the stream sediments is studied by multivariate data analysis methods.Results of data analysis show that stream sediments act as a complex oxidising-adsorption barrier and the heterogeneity of the geochemical barrier is controlled by redox gradients in the sediments, which can be sufficiently characterised by the distribution of Fe fractions. Data analysis suggests that adsorption and co-precipitation with Fe oxy-hydroxide are major processes beside the adsorption on organic matter. Mn is probably specifically adsorbed on Fe oxy-hydroxides, and beside Zn, it is least retained in the sediment. Pb, Cu and Ni are found in considerable quantity in the reducible fraction and are suggested to occur occluded in Fe oxy-hydroxides. On the other hand, organic matter provides important adsorption sites for Cu and Pb and controls exchangeable metals, too. Based on enrichment factor calculation and correlation analysis in the pore water and the oxide-bound fractions Ni, Cu and Zn are thought to represent the effects of ore mining.