Spatial distribution of trace and rare earth elements of bottom sediments in Lake Ostrowite, Bory Tucholskie National Park, Poland

Lake pollution has attracted concerns worldwide; especially the excessive accumula-tion of trace elements (TEs) and rare earth elements (REEs) in bottom sediments canpose a serious threat to ecosystem health. However, there is still a knowledge gap onthe level of sediment pollution in lakes isolated from the direct impact of pollutionsources, their spatial variability, and also on the factors influencing this state. The aimof this study is to investigate the level and spatial variability of TEs and REEs concen-trations, as well as to determine their source and the factors determining their distri-bution in the bottom sediments of Lake Ostrowite. Lake Ostrowite is the largest anddeepest water body located in the Bory Tuholskie National Park (in northern Poland),which completely isolates the lake from the direct impact of pollution sources. Thestudy covered analyses of 32 surface samples of bottom sediments. The concentra-tions of 24 TEs and 14 REEs were determined using inductively coupled plasma massspectrometry (ICP-QQQ-MS). The assessment of the enrichment of bottom sedi-ments in TEs and REEs employed geochemical background values (GBV) that pro-vided the basis for the calculation of relative concentrations and geochemical indices.The determination of their sources and supply routes was based on the cluster analy-sis and principal component analysis. The obtained results point to the enrichment ofthe bottom sediments with TEs and REEs. Relative concentration values of TEs andREEs in reference to geochemical background values were in ranges from 0.01 to7.31, at an average of 0.99, and from 0.03 to 4.29, averaging 1.76, respectively. Theenrichment factor values show moderately severe enrichment of sediments at thestudy sites. This was primarily determined by the concentrations of Ag (from the TEsgroup) and Lu (from the REEs group). The metal pollution index values showed anapproximate spatial distribution of points in terms of the presence of TEs and REEs.The lowest concentrations of TEs and REEs occurred on the eastern shore of thewestern basin of Lake Ostrowite. TEs and REEs concentrations in sediments are posi-tively correlated with the content of organic matter and depth and negatively corre-lated with distance of the sampling point from the river outflow from Lake Ostrowite. On the eastern shore of the western basin, TEs and REEs concentrations are addition-ally shaped by wind, predominantly from the western direction. With water waveaction, organic matter is transported to the central part of the western basin, where itis accumulated. Since the lake is isolated from point and nonpoint pollution sources,relevant from a biogeochemical point of view are dry and wet depositions from theatmosphere as well as aquatic vegetation, shoreline vegetation, forest litter, soil, andgroundwater.