Abundance and fractionation patterns of rare earth elements in streams affected by acid sulphate soils

Abstract

The abundance and shale-normalised fractionation patterns of rare earth elements (REEs) were studied in 121 streams of first and second order in an area where acid sulphate soils, developed on oxidised sulphide-bearing marine sediments, are abundant. During high-water flow events in autumn, on which this study focuses, the leaching of REEs from the acid sulphate soils is extensive, resulting in high total REE concentrations (up to >1 mg/l) in streams draining such soils exclusively. In these streams, there is a general depletion of the heavy REEs explained by preferential scavenging of the latter by oxyhydroxides in the deepest soil-profile horizons. In streams draining areas of glacial till and peat, the REE concentrations are several orders of magnitude lower. In these streams, in contrast to the REE-enriched streams, there is a depletion of light REEs explained most likely by preferential complexation of the middle and heavy REEs by dissolved humic substances.