The study of groundwaters was carried out in two different forest ecosystems of Słowiński National

Park: Vaccinio uliginosi-Betuletum pubescentis and Empetro nigri-Pinetum in the period of 2002-2005. Differences were found in the position of the groundwater table and in the concentrations of nitrogen and phosphorus

compounds in the investigated forest associations. In the Vaccinio uliginosi-Betuletum pubescentis association

the groundwater table was found on average at a depth of -73.3 cm, while in Empetro nigri-Pinetum at -90.2

cm. No statistically significant effect of precipitation on the position of the groundwater table was found in

this study. Statistical calculations (U Mann-Whitney test) for groundwaters in the analyzed forest associations

showed statistically significant differences in the dynamics of concentrations of total nitrogen (T-N), organic

nitrogen (Norg.), nitrate nitrogen (N-NO3

), total phosphorus (T-P), organic phosphorus (Porg.) and the level of

groundwaters.

The intensive agricultural use of the land affects both quantity and quality of river water in the catchment area. Such impact is visible also in the Szreniawa River catchment in the Małopolskie Voivodeship. The combination of intensive plowing and soil susceptibility to water erosion are the main causes of soil and nutrients depletion during the heavy rainfall. The aim of the study is to determine changes in the water quality in the Szreniawa River catchment compared to the agri-culture use and precipitation level.

The quality of surface water has been analysed in the river catchment area in three sampling points. The concentration of the total suspended soils in the samples collected after heavy rainfall in August 2017 reached a value of 837 mg·dm–3. The average concentrations of N-NO3 in the years of 2016–2019 ranged from 0.16 to 13.46 mg·dm–3, with the highest val-ues in the summer (up to 13.46 mg·dm–3). The concentration of N-NH4 and P-PO4 in the Szreniawa water was affected by precipitation. The highest value of average concentration of N-NH4 3.00 mg·dm–3 was recorded in the autumn of 2019 in the middle section of the river. The highest value of P-PO4 0.90 mg·dm–3 was recorded in the autumn of 2019 mostly due to water erosion of the loess areas. Erosion has been caused by the short-term heavy rainfall. As a result, suspended solids, soluble and insoluble phosphorus compounds leaked to the river.

The aim of the study was to assess the P-PO4 and N-NH4 pollution of water in grasslands located on peat soils and to identify the impact of groundwater level on this pollution formation. The research was conducted in 2000– 2010 on grounds of ITP-PIB in Biebrza village (Poland). Within lowland fen a total of 18 monitoring points of groundwater and watercourses were established in 6 separate test stands. The subject of the research was water collected from drainage ditches/channels and groundwater, which was taken from wells installed in organic-soil layer and wells whose bottom was 15–20 cm below this layer. Water samples were collected several times a year, and in the case of groundwater, its level was also measured. It was found that: 1) due to concentration level of P-PO4 and N-NH4, about 46 and 39% of water samples from organic-soil layer and more than 40 and 37% of water samples from mineral- organic-soil layer respectively, were characterized by poor chemical status; 2) due to the exceeding of the limit values of P-PO4 and N-NH4 concentration, water samples from watercourses in over 30 and 27% respectively were not within 1st and 2nd class of surface water quality; 3) P-PO4 and N-NH4 concentrations in each water type were statistically significant and positively correlated with each other; 4) in organic-soil layer the groundwater level changing every 10 cm was a statistically significant factor differentiating the average P-PO4 concentration in groundwater associated with mineral-organic layer of peat soil and average N-NH4 concentration in each type of water.