The aim of the research was to determine the factors defining the growth and development of Lolium perenne and Trifolium repens upon petroleum contamination. The top layer of clay soil contaminated with petroleum products resulting from an oil pipeline failure was collected for the tests. The control was the same type of uncontaminated soil with the addition of, under laboratory conditions, tissue paper. The research was conducted in two stages. The first concerned the germination process and seedlings parameters (Petri dishes). The germination energy ( GE) and the germination capacity ( GC) of seeds were determined. The seedling’s development was also evaluated based on ‘WinRhizo PRO 2009’ software. Then, in the second stage, pot tests were carried out, where the growth and development of species in the first year after sowing were temporarily measured. The parameters studied were the number, height, green and dry masses of the plants.
A Gompertz regression model describing seed species germination and number species as time dependent dynamic was applied. The data were analysed statistically using variance analysis (ANOVA) and the PCA (principal component analysis) method. The results of our study indicated that admixture of petroleum into the soil does not seriously affect the development dynamics of Lolium perenne seedlings. The diesel oil contamination mostly affects the germination of the Trifolium repens by a statistically significant increase of the maximum value of germination and increasing the maximum growth rate.

The aim of the study was to determine the extent to which created and functioning beaver dams contribute to increasing water retention in the Łąki Soleckie facility (Mała River valley). Changes in the plant cover of meadow habitats within the range of beaver dams were also determined. During the growing periods in 2020–2022, measurements of the periodic levels and water retention of the Mała River and the adjacent ditches (R-27, R-29) were closely related to the activity of beavers and precipitation. The maximum volume of water retained in the Mała riverbed in 2020–2022 was 1,300, 1,700, and 1,200 m³; the maximum retention of the R-29 ditch was 270, 210, and 200 m³, respectively. In 2021–2022, the R-27 ditch collected the most water – 270 m³and 250 m³. Starting from June 2022, due to beaver dams D2 and D3, the water level in the river and water retention have stabilised at a high level, despite slight rainfall. The activity of beavers contributed to the transformation of communities of wet habitats located on organic soils (Calthion) into communities of periodically wet habitats (Caricetum gracilis). In places where natural habitat 6510 occurs, the coverage of species of the Festuca genus has increased, and the value of the biodiversity index has increased by an average of 9%. High stability in the community of expansive species (Deschampsia caespitosa and Veronica longifolia) and their increasing cover may make it difficult to maintain the proper condition of natural habitat 6510.