Zmiany stanów wód gruntowych w Puszczy Zielonka w okresie 1970–2009

The aim of this study is demonstrate trends of groundwater level changes in Zielonka Forest on the Experimental Forest District Potasze example. The study included a period of 40 years (1970–2009). Variability of groundwater conditions is basis of water relation ratings, or trends of changes on given area, particularly on forest area. The Zielonka Forest is situated in the middle section of the Warta river catchment, in the central part of the Wielkopolska region, and its western border lies about 6 kilometres north-east of Poznan. The area is situated in the western part of the Wielkopolska-Mazovian climatic region. The natural landscape is of early glacial type of Pleistocene and Holocene formation. Postglacial drifts, deposits from the Poznan stage of the Würm glaciations, are the main parent materials of the soils in this area. The granulometric composition is formed by sands with a low clay content, overlying loose sands with admixture of gravel and slightly sandy clay. Scots pine (Pinus silvestris L.) is the dominant tree species but also oak (Quercus robur. L., Q. petrea (Matt.) Liebl.), alder (Alnus glutinosa (L.) Gaertn., Alnus incana (L.) Moench.), larch (Larix sp. Mill.) and rarely spruce (Picea abies (L.) Karst) occur there. The predominant forest site types are: fresh mixed coniferous forest, fresh coniferous forest, wet coniferous forest and alder swamp forest. The greatest yearly fluctuations in groundwater level were observed in alder/ash swamp forest site types, where groundwater level was the highest (in shallow groundwater). Extended the meteorological observations on Zielonka station for 1970–1985, based on meteorological observation from Poznan station are reasonable. The resulting regression and correlation coefficients relation for precipitation sum, mean air temperature (monthly and annual) are statistically significant on customarily accepted levels of significance α = 0.05. Consequently complete data of precipitation and air temperatures have been obtained for the study period 1970–2009 for the Zielonka Forest representative meteorological station in Zielonka village. Time trend for annual precipitation sum in Zielonka Forest in the period 1970–2009 is not statistically significant. However, time trend over that period of the average annual air temperature in the Zielonka Forest is statistically significant and amounts to about +0.05°C/year. These trends for the last 10 years during the study period are respectively -0.28 mm/year and +0.11°C/year. These figures can be considered as a confirmation of the adverse climate changes described in the IPCC Report (2007), in relation to the studied area. For the analysis of groundwater conditions selected years 1970, 2002 and 2009. According to the meteorological conditions (precipitation, air temperature), these three years can be regarded as the average (normal). Average groundwater levels in Zielonka Forest (based on Forest District Potasze analyses) throughout the 40-year study period (1970–2009) fell by about 50 cm, while in the last seven- years, fell by 20 cm. Assuming an average porosity of the aquifer layers to 34%, respectively in these periods decreases the ground retention were thus about 160 mm and 60 mm. Variability of groundwater levels has been reduced twice (variation coefficient of groundwater levels dropped by half). The largest groundwater decreases recorded on forest site types. Much lower on coniferous forest and alder/ash alder swamp forest site type. Groundwater lowering in Zielonka Forest can be associated with intensified adverse climate changes. But this is not the only explanation. The second factor, adversely effect on groundwater conditions in Zielonka Forest and its buffer zone, which was not the subject of this paper, is so-called anthropopressure. For example residential and recreational buildings, manufacture and process plant, etc.