Abstract Before 1925, an artificial lake (TR-17) was created in a pit excavation in the area of Łuk Mużakowa (southwestern Poland). During the nineteenth century, this area was an active lignite mine, which means that its location was within the range of acid mine drainage (AMD). Between 1928 and 1943, the lake was transformed into a municipal bathing area with developed infrastructure. In the 1970s, a pig farm and meat-processing plant were in operation. Sewage resulting from pig farm and meat production was released directly into the surrounding fields causing eutrophication. Together with surface and ground water, nutrients and toxic metals were delivered to the lake, impacting the phyto- and zooplankton communities. Changes in the lake trophic state and pollution were inferred from diatom, Cladocera, and chrysophyte–stomatocyst assemblages, supported by geochemical analyses, including the C:N ratio and concentrations of heavy metals such as Cr, Co, Cu, Ni, and Zn. After the closure of the meat-processing plant, the lake began to recover from both eutrophication and heavy metal pollution. During that time, other factors, such as liming and fish stocking, affected the development of phyto- and zooplankton. However, the presence of AMD around the lake, along with processes releasing sulfuric acid and heavy metals as a result of the oxidation of sulfide minerals, have caused the reacidification of the lake since 2009. Heavy rainfalls in 2010 contributed to an increase in weathered materials entering the lake. The results show that various stressors significantly affect the conditions of the lake ecosystem. At the same time, we found that it is often difficult to clearly determine which factor had the greatest impact on the lake’s current state. In the case of Lake TR-17, AMD appears to have been the dominant influence, except during the 20 year period of the pig farm’s operation, when the inflow of domestic sewage from animal husbandry played a more significant role.

Abstract Gravity sediment corers have long been useful in recovering lake sediments for paleoenvironmental analysis, particularly in deep lakes or other situations that preclude the use of other coring systems. However, they have been limited to a single sediment recovery drive. The gravity coring system described in this paper is capable of single or multiple sediment drives and can be constructed out of commonly available materials.

Abstract The study of ancient sedimentary DNA (sedaDNA) aims to reconstruct the past environments and understand the historical biodiversity in or around aquatic ecosystems. The 18S ribosomal RNA gene (18S rDNA) is usually the target for discerning a broad spectrum of eukaryotic organisms, mainly microbial. Depending on the scientific context, metabarcoding of three hypervariable gene regions (V4, V7, and V9) are the most used alternatives for characterizing aquatic communities. Here, we evaluate the pros and cons of the three regions using sedaDNA samples up to about 3300 years old from a high mountain lake sediment. In samples with sufficient DNA content (ca. 1 µg DNA/g wet sediment) and preservation, V4, the longest region, provides community reconstructions richer in taxa. However, when DNA deterioration becomes more pronounced (i.e., > 1300-year-old samples in this study), the performance of the shortest V9 region is more satisfactory. The V7 region provides intermediate results. The three regions show biases concerning high taxonomic ranks, with V7 and V9 regions performing similarly. Microbial eukaryotes are better assessed than metazoans, and Kinetoplastea (Euglenozoa) are particularly persistent in ancient samples.

Abstract Iron (Fe) concentrations are increasing in lakes on a wide geographical scale, contributing to recent browning of lake waters. As available time series on lake-water Fe concentrations are relatively short, covering the past few decades only, varved lake sediments may provide extended and precisely dated records to study temporal Fe dynamics in lakes in response to environmental drivers, such as changes in catchment land use and atmospheric sulphur deposition. Here, we present and discuss temporal changes in Fe speciation and accumulation rates during the last three centuries as revealed by sub-annually resolved X-ray absorption spectroscopy analyses of varved sediments from three lakes in southern Finland. Iron speciation in sediments is dominated by Fe-bearing silicate fractions in two of the lakes, while the third lake has contributions of organically complexed Fe and Fe-(oxy)hydroxides. Long-term changes in sediment Fe accumulation correspond with documented shifts in land use from agriculture to spruce forestry in the lake catchments, and in one of the lakes with water-level lowering. An overall poor correspondence between monitored aqueous Fe concentrations and sediment-inferred Fe accumulation rates is likely linked to the dominance in the sediments of particulate Fe phases that are not prevalent in suspended form in the water column. This suggests that sediment records are unsuitable for reconstructions of past lake-water Fe concentrations in these lakes. However, the study provides valuable insight into how major land-use changes in the past have affected both the supply and speciation of Fe accumulated in lake sediments.