This study includes hydrologie characteristics of the Potok Toszecki basin area and the results of chemical analysis of water quality of the Potok Toszecki. These investigations were carried out in following periods: from March 1993 till May 1994 and from January 1997 till June 1998. The results of investigations on the chemical parameters of water quality were compared with analysis, carried out in 1976. Under the results of this investigations water quality of the Potok Toszecki - a watercourse, which flows to the Pławniowice Reservoir - was defined and essential factors, connected with character of the basin area have been shown. Classification of several parameters was achieved under the official decree of the ministry of environmental protection from November 5th 1991. On the basis of this classification it was found, that the main risk for the Pławniowice Reservoir are biogenie substances and suspension, inflowing to the Reservoir together with the water of the Potok Toszecki. Improvement of the existing situation will be possible only if firm waste-water managements action will be taken.

The article presents the results of research aimed at determining the catchment areas that pose a risk of nitrogen pollution of the waters of the Mała Panew river. The research was carried out in 13 permanent monitoring points located on the Mała Panew. The location of the points ensured the representativeness of the water quality results for parts of the catchment area with a homogeneous type of land use. Concentrations of nitrate-nitrogen (NO3-N) and total nitrogen (TN) were determined in the samples taken. The content of (NO3-N) in the third quarter of the year and its relation to the value obtained for the first year quarter may be an indicator of the impact of agricultural activities on the quality of water in streams. In the case of agricultural catchments, the lowest concentrations of NO3-N and TN occur in the third quarter of the year and are significantly lower than in the first quarter of the year. The demonstrated seasonal variability of nitrate nitrogen concentrations in agriculturally used areas may be used to determine the type of pressure not allowing to achieve good water status in the surface water body. It was shown that the highest unit increments occurred in areas with a high proportion of forest.

Water erosion in mountainous areas is a major problem, especially on steep slopes exposed to intense precipitation. This paper presents the analysis of the topsoil loss using the SWAT (Soil and Water Assessment Tool) model. The SWAT model is a deterministic catchment model with a daily time step. It was designed to anticipate changes taking place in the catchment area, such as climate change and changes in land use and development, including the quantity and quality of water resources, soil erosion and agricultural production. In addition to hydrological and environmental aspects, the SWAT model is used to address socio-economic and demographic issues, such as water supply and food production. This program is integrated with QGIS software. The results were evaluated using the following statistical coefficients: determination (R2), Nash–Sutcliff model efficiency ( NS), and percentage deviation index ( PBIAS). An assessment of modelling results was made in terms of their variation according to different land cover scenarios. In the case of the scenario with no change in use, the average annual loss of topsoil (average upland sediment yield) was found to be 14.3 Mg∙ha ^–1. The maximum upland sediment yield was 94.6 Mg∙ha ^–1. On the other hand, there is an accumulation of soil material in the lower part of the catchment (in-stream sediment change), on average 13.27 Mg∙ha ^–1 per year.