Trends in Trace Element Concentrations in Holocene Bottom Sediments of a Lake Wielki Staw in the Karkonosze Mountains

Lake sediments and peat bogs are natural archives of long-term changes in the quality of the natural environment at local and regional scales. However, due to technical difficulties the sediments of mountain lakes are rarely subject of geochemical analyses. Also, the sediments of Wielki Staw (1,225 m a.s.l.), the largest lake in the Karkonosze and entire Sudeten Mountains, have never been analyzed for trace elements. The aim of this study was to determine total content of Pb, Cu, Zn, Cd, Ni, Cr, Mn, and their vertical variations on the background of basic physical and chemical properties of sediments of Wielki Staw. The 11 m-thick sediment profile, representing the entire Holocene period, was analyzed after being divided into 55 sections, each 20 cm thick. Bottom sediments are characterized by variable particle-size distribution (prevailing loamy textures), strongly acidic pH, and high content of organic matter and Fe (2,730-10,100 mg.kg(-1)), but low Ca (70-688 mg.kg(-1)) and Mg (567-2,450 mg.kg(-1)). Mean concentrations of trace elements are lower than in the sediments of Polish lowland lakes and close to the contents in mountain peatbogs and soils, and are generally correlated with the organic matter and fine earths. Pb, Mn, Zn, and Cu concentrations (4.65-81.8, 85.4-346, 11.9-50.3, and 3.05-19.5 mg.kg(-1), respectively) are generally higher in the oldest (pre- and boreal) sediments and lower in younger sediments (postatlantic). Cr, Ni, and Cd (0.55-10.7, 1.40-7.35, and 0.25-1.15 mg.kg(-1), respectively) contents do not express any trend throughout the profile. Increases of Cu, Zn, and especially Pb concentrations in the uppermost layer of sediments (down to 1.2-1.5 m) is not justified by the change of the physicochemical properties of sediments and may only be explained with atmosphere anthropogenic contamination in the Sudeten Mountains that began at the end of the first millennium AD and accelerated during the last three-four centuries.