The paper presents the results of research into toxic metal concentrations in the surface layer of bottom sediments in Lake Gopło. The research objectives were to identify the levels and spatial variability of Cu, Pb, Cd, Zn, Ni, Cr, As and Hg concentrations, their potential sources and the determinants of pollution levels. Metal contamination of the sediments was assessed using the geoaccumulation index (Igeo), pollution load index (PLI) and ecological risk index (RI). Chemometric methods (Pearson correlation, principal component analysis (PCA) and cluster analysis (CA) were used to determine the relationship between sampling sites and concentrations of toxic metals, thereby identifying the sources of contamination. The research found that grain-size composition, carbonate content and organic matter content in the bottom surface sediments of Lake Gopło are all characterised by low diversity. Therefore, the lithological features of the sediments are not a major factor in the concentrations and spatial variability of the metals. It was found that the metal concentrations in the great majority of samples were above regional geochemical background levels. The geochemical indices (Igeo, PLI, RI) indicate that the degree of toxic metal pollution in the sediments is slight in the central and southern parts of the lake and high in the northern part. The chemical analysis results showed that the samples in the central and southern parts of the lake differ little in their shares and concentrations of individual metals. This provides evidence that, as well as geogenic sources, their presence in sediments can be associated with non-point sources related to agricultural activities and with atmospheric sources (mainly the products of fossil fuel combustion). The higher concentrations of metals (especially Ni, Cd, Cr and Hg) in the northern part of the lake are influenced by the supply of industrial and communal pollutants from the lakeside town of Kruszwica. A factor limiting the migration of pollutants from the northern part of the lake towards the south is the lake’s morphology of the lake, which hinders water exchange between the northern part and the rest of the lake.

This paper presents the results of the study on the concentration of heavy metals and persistent organic pollutants (POPs), including PAHs and PCBs, in the bottom sediments of Lake Gopło. This lake is significantly elongated (about 25 km); its longitudinal profile is diversified, and there are deeps and thresholds impeding the flow of water. The shoreline is varied, which is characteristic of tunnel valley lakes. The catchment has a typical agricultural character with a point arrangement of industrial centres. The analysis of the diversity of the concentration of heavy metals and POPs was based on 37 samples from two representative cores: one collected in the northern part of the lake, the catchment of which shows an industrial character, and the second one in the southern part where the catchment is agricultural in character. In the sediments, the content of the following heavy metals was analysed: Cu, Pb, Cd, Zn, Ni, Cr, Hg and As, as well as PAHs and PCBs. The sediment age was determined by the ²¹⁰Pb dating method. In order to assess the contamination level of the bottom sediments with heavy metals, the contamination factor (CF) and degree of contamination (DC) were calculated. Moreover, the impact of the changes in the catchment’s land use over the past 100 years was determined. The results showed that the sediments from the industrial part of the lake significantly exceed the geochemical background for both the heavy metals from the group identified as industrial pollution and from the group of agricultural pollutants. The southern core shows only a slight increase in the amount of pollution from the agricultural group, lack of industrial pollution and a low degree of contamination. A slight increase in persistent organic pollutants is also recorded, without any apparent effect on the state of the deposited sediment. The ²¹⁰PB dating enabled the main stages of human impact to be determined: the pre-industrial revolution, from the beginning of industrialisation to the 1950s, intensive human impact from the 1960s to the 1980s, and a gradual decrease in the human impact starting from the 1990s. In addition, attention was paid to the changing sedimentation rate.

The study objective was to prepare a quantitative inventory of lakes and to assess their long-term changes. The research area included the Osa river basin (northern Poland), which is located in a lake district. The research was based on historical cartographic materials published in 1900-1947 (German 1:25,000 ‘Messtischblatt’ topographic maps) and modern topographic maps from 2010 (The 1:50,000 Digital Map of the Hydrographic Division of Poland [MPHP]. The number of lakes increased from 173 to 235, while the total surface area of the lakes fell by 107.55 ha. The largest number of lakes belonged to the 1.0-5.0 ha range on both MPHP and Messtischblatt maps. It was in this range that the largest increase in number of lakes and lake area relative to the historical maps was found. A significant reduction in area of lakes was recorded in the group of lakes with an area from 50 to 100 ha.

The variation of water velocity in an artificial dam reservoir is influenced not only by the inflow discharge, but also by the bathymetry of the reservoir and the water level at the dam. The depiction of spatially complex variations in flow velocity through a reservoir would not be possible without the use of hydrodynamic models. A reliable hydrodynamic model of the reservoir is an effective tool for predicting and analyzing changes in the reservoir geoecosystem in an age of changing climate and risk of water stress. A depth-averaged two-dimensional AdH model was used to visualize the hydrodynamics of the Włocławek Reservoir. Running the model for eight different hydrological conditions delivered consistent results and allowed to calibrate the model parameters. Additionally, it provided a way to verify the data regarding the rating curve of the Vistula River upstream the reservoir.

This article presents maps of reconstructions of selected primary (i.e. prior to the thirteenth-century founding of the town) abiotic components of the natural environment of medieval Toruń (northern Poland, Kuyavian-Pomeranian Voivodeship) and its close suburbs. The reconstructions were carried out on the basis of topographical, geological and historical data. Despite their many limitations, the procedures employed represent the first attempt at a quantitative reconstruction of the primary relief, surface geology and hydrology of the analysed area. The result of the reconstruction presented on the maps could be used as the basis for both a reconstruction of biotic components of the natural environment and verification of hypotheses regarding the conditions of the founding and spatial development of the town.