Partitioning of metals between operational fractions in the sediment record from Lake Peipsi

A sequential extraction procedure was used to study the partitioning of metals (Ca, Mn, Fe, Cu, Zn and Cd) between operationally defined fractions in the interval covering the last 150 years of the sediment record from Lake Peipsi, Estonia. The results indicated decreased total and bioavailable Cu and Zn levels from the 1980s to the present, and increased Cd. The variability in Mn and Fe concentrations was possibly induced by changes in redox conditions at the bottom of the lake. The dissolved organic fraction of the sediment core was characterised by high-performance size-exclusion chromatography and spectroscopy. The dissolved organic matter pool was comprised mainly of humic substances and of a very small high molecular weight fraction. This study revealed increasing trends for general sediment characteristics (organic matter, dissolved organic carbon and absorbance ratio) since the 1960s, together with some molecular characteristics (peak areas of humic and high molecular weight fractions). Statistical cluster analysis revealed that metal concentration data in combination with some chromatographic and spectrometric parameters can be used to reveal periods with similar characteristics in Lake Peipsi sediments.