Trends in Level of the Groundwater Table in the Selected Catchments in the Zielonka Forest

The aim of the study was to assess changes in the position of the groundwater table in selected catchments in the Zielonka forest. The paper presents the results of researches carried out at Hutka small catchment up to Huta Pusta cross section and Potaszka small catchment up to Potasze cross station. Analyzed catchments of investigated watercourses are located in the central part of the Wielkopolska region, approx. 20 km north-east of Poznań, in the Zielonka Forest, at a distance of approx. 7 km from each other. The catchment of the Hutka watercourse, with an area of 0.52 km2, is forested in 89%, the other 11% being covered by swamps and wasteland. The predominant sites are fresh mixed coniferous forest (BMśw), fresh coniferous forest (Bśw) and alder swamp forest (Ol). The catchment of the Potaszka watercourse is over two times bigger, with an area of 1.33 km2. Here forest cover only 14.7% catchment area, arable land (GO) occupies approx. 75%, while grassland (UZ) constitutes 10.3%. Landscape in both catchments is characterized by a large number of interior depressions, filled partly with rainwater or peat bogs, with poorly developed natural drainage During the research detailed analyses were made for the dynamics of the ground water level. The researches curried out in different habitat conditions in watercourses Hutka and Potaszka catchement indicated that the highest amplitudes oscillations ground-water levels, in winter and summer hydrological half-year, occurred in older swamp forest, whereas the smallest in fresh mixed coniferous forest. The research proved, that the dynamics of the soils humidity variation and ground water level in analyzed drainage catchment is described by similar cyclist and depends mostly on the course of meteorological conditions, especially on the distribution and dimension of rainfalls. It was confirmed that the low level of groundwater table in the vegetation season does not affect significantly the water reserves of the surface layer of soil. Additional elements affecting the level of ground water are also: the distance between measuring wells and the watercourse, site type and the layout of the land