Anomalies of rare earth elements and heavy metals/metalloids in modern sediments of small lakes in the north of Karelia (Arctic): geology and technogenesis influence

Abstract

Lake sediments are used as indicators of the condition of water bodies and the changes that have recently occurred in them and in their catchments. This work for the first time detailed examined two small lakes in Northwestern Russia (Arctic). Sediment cores were collected from the center of each lake and separated into 1 cm layers. An ICP-mass spectrometer was used to determine the chemical composition. It was found that both lakes have sediments containing organic matter (up to 61%). In both lakes, the content of rare earth elements, Th, V, Cr, and others, was found to be elevated relative to the background levels of the region and the average content in the Earth’s crust. It was established that in the sediments of Lake Aprelskoe, the total concentration of rare earth elements (1916 mg/kg) exceeds or is at the same level as the similar values of rare earth elements in lakes near cities and industrial enterprises. Such high concentrations of REE have not previously been found in pristine lakes. An analysis of the geological conditions of the study area and adjacent territories (Karelia, Finland) showed that the source of anomalies of rare earth and other elements in the studied lakes may be bedrock containing increased concentrations of Y, Ce, La, and other elements (Zr, Ta, Ba, Th). However, an analysis of the geochemistry of the studied sediments also indicated technogenic influence on the lakes: an increase in the concentrations of Pb, Sd, Cd, Ni, and Cu in the uppermost layers of the lakes’ sediments was established. Suspected sources of pollution are metallurgical plants in the neighboring region and the effects of long-range transport of metals due to coal burning around the world.