Geochemical Landscape Analysis for the Risk Assessment of Acid Mine Drainage in a Wetland Environment

Abstract: Attenuation of acid mine drainage (AMD) metals originating from abandoned mines and waste rock dumps is investigated in this thesis at Slättberg in central Sweden, where acid mine leachate has been discharging for over 70 years into the receiving wetland stream and mire. Risk assessment of AMD and related polluted lands requires a holistic approach that is able to study the complexity of pollution emissions and impacted landscapes. In this thesis a link between geochemical contaminant fate modelling and landscape analysis is presented for AMD risk assessment. A simple geochemical landscape analysis tool is developed to analyse and model geochemical abundances, geochemical gradients, geochemical flow patterns and geochemical barriers in the studied stream and mire sediments. Sampling locations at geochemical barriers are identified using landscape geochemical and GIS methods. A sequential chemical extraction procedure is used to investigate fractions which are expected to act as potential sinks of the six studied metals (Cu, Fe, Mn, Ni, Pb and Zn) in the sediments. For data modelling robust statistical methods of Exploratory Data Analysis are used to treat small sample sizes with multimodal character and outlying values. The spatial variability of metal retention in the sediments is studied by multivariate data analysis methods. Results show that the developed simple geochemical landscape analysis method can be used efficiently for the risk assessment of toxic mine contaminants in the complex receiving wetland landscape. It is suggested by the analysis that the oxidising geochemical barrier in the stream sediments can be sufficiently characterised by the distribution of Fe fractions. At the AMD discharge location metal sulphide formation and organic matter adsorption control metal retention in the mire. Mires are very sensitive to changes in hydrological conditions and drying of the sediments leads to erosion and hence the release of adsorbed metals to the environment.