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Large watercourses are characterised by significant spatial and temporal changes in water quality due to both natural and anthropogenic impacts. The paper analyses changes in the Danube's spatial and seasonal water quality in its middle part at five monitoring stations for the period 2018–2022. Examined water quality parameters include oxygen saturation (Os), ammonium (N-NH4), pH, 5-day biochemical oxygen demand (BOD), nitrate nitrogen (N-NO3), orthophosphates (P-PO4), suspended solids (SS), electrical conductivity (EC), and water temperature (WT). Furthermore, the analysis took into account the influence of two additional factors: air temperature (AT) and discharge (D). Throughout the entire period under study, all parameters were characterised by low concentration values, which met the environmental objective of good ecological status. The use of multivariate statistical methods allowed for the identification of EC, N-NH4, WT, Os, SS, and N-NO3 as determining the greatest spatio-seasonal variability of water quality in a selected section of the Danube. Regression models determined WT, EC and nitrogen nitrate changes as depending on AT, flow, and exposure time. Knowing models not only gives a better understanding of the dynamics of changes in water quality in the stretch of the Danube under study but potentially allows the prediction of these parameters based on easily measurable environmental variables. [ABSTRACT FROM AUTHOR]

The occurrence of the protected species Castor fiber L., which creates a network of natural barriers for its own needs, may affect the changes in water quality parameters. This study shows changes in the water quality parameters (EC, BOD5, COD, TN, N-NH4, N-NO3, N-NO2, TP, P-PO4, Cl−, SO42−) of small rivers in eastern Poland. The results were analysed using the one-way and three-way ANOVA Tukey's HSD post hoc test to identify the significance of the changes in the water quality parameters for habitats, seasons, and land use. All parameters, with the exception of P-PO4, met the standards of a good ecological status. The average values of P-PO4 exceeded the threshold of the good ecological status in summer and meadows. The average annual changes in the water quality parameters, with the exception of N-NH4, are characterised by a decrease in pollution. The highest concentration decrease of 57% was found for P-PO4 and 45% for TP at the sites after the barriers. The lowest concentration decrease of 5% was found for EC. In the case of N-NH4, the concentration increase was 33%. The situation was completely different in the case of removing barriers, where an increase in the concentration of pollutants of about 30% was found. Changes in the water quality were significantly influenced by the season and land use. Due to the various construction, age, and removal of the barriers, beaver habitats may positively or negatively impact the water quality. It is crucial for the improvement of the water quality to ensure the durability of the functioning of barriers and the proper use of the land. [ABSTRACT FROM AUTHOR]

Introducing the European beaver to the catchment area, which adjusts the habitat to its own needs (by building dams), may have a positive impact on the ecology, geology, and hydromorphology of rivers and intensify the water self-purification process. In this study, a comparative assessment of the ecological status was made between the areas where the species Castor fiber L. occurs (habitat type A) and the areas unaffected by the influence (habitat type B). For this purpose, the Macrophyte River Index (MIR) and the Hydromorphological River Index (HIR) were calculated, along with the floristic indicators of biodiversity: species richness and Margalef, Shannon–Wiener, and Simpson indices. Only 35% of the sites met the standard of good ecological status. The presence of hypertrophic species and anthropogenic modifications of the river bed had a negative impact. The spread of beavers has a significant positive effect on changes in hydromorphological conditions and water levels in the river. The water levels in habitat types A and B were 0.504 and 0.253 m, respectively. There were statistically significant differences in the HIR values between habitat types A and B, which were 0.585 and 0.535, respectively. In habitats of type A, the heterogeneity of the current and bed material as well as the diversity of elements accompanying the tree stands increased. Research has shown greater species richness and greater biodiversity of macrophytes in the habitats of beaver dams. The research confirmed the significant influence of the European beaver on changes in the environment. The activity of beavers intensifies the processes of introducing wetland and rush species to forest areas. [ABSTRACT FROM AUTHOR]

The aim of the study was to analyze the results of surface water quality tests carried out in the Bystrzyca river basin. The study was conducted over four years in four seasons. The following chemometric techniques were used for the purposes of statistical analyses: the principal component analysis with factor analysis (PCA/FA), the hierarchical cluster analysis (HCA), and the discriminant analysis (DA). The analyses allowed for determining the temporal variability in water quality between the seasons. The best water quality was recorded in summer and the worst in autumn. The analyses did not provide a clear assessment of the spatial variability of water quality in the river basin. Pollution from wastewater treatment plants and soil tillage had a similar effect on water quality. The tested samples were characterized by very high electrolytic conductivity, suspended solids and P-PO4 concentrations and the water quality did not meet the standards of good ecological status. [ABSTRACT FROM AUTHOR]