Czasowa zmienność zawartości wybranych składników rozpuszczonych w wodach gruntowych układu katenalnego na Pojezierzu Poznańskim

This paper presents results of temporal variability of groundwater chemical composition in catena of arable Albeluvisols and Gleysols/Chernozem. The purpose of this study was to assess temporal variability of dissolved components in groundwater with particular reference to soil toposequence. The researches were carried out in the cultivated catchment area of the Przybroda Experimental Station located in the north-central part of the Poznań Lakeland (west part of Poland) within the Szamotuly Plain. Every two or four weeks from 2004 to 2006 the groundwater samples from six stationary points (wells) were collected. In groundwater samples the Ca2+, Mg2+, K+, Na+, HCO3-, SO2-4, PO43-, pH and EC were determined. Temporal variability of dissolved components in groundwater of catena was determined using the geostatistical analysis in which the semivariance is the basic function. Relations between values of semivariance and time correlation ranges were determined using the Variovin and the Surfer programmes. The purpose of this study was to evaluate the temporal variability of concentrations of the selected components dissolved in groundwater using geostatistical methods. The results of the researches indicate, that the quantity of dissolved components in groundwater was connected with a soil location in a relief and properties of soil parent materials. The groundwater of soil located higher in a catena ware characterized by smaller concentrations of the analyzed components, compared with water of lowest elements of the slope. The results show that temporal changes in the content of the analyzed components were characterized by large values of systematic variability and small values of random variability (nugget effect). Low nugget effects indicate that the temporal changes in concentration of the analyzed components were temporary correlated. Systematic variability was characterized by two temporary structures. The first concerns the systematic changes in shorter periods of time, which could be the result of groundwater inflow of compounds dissolved in percolating water and lateral inflow and outflow. The second was characterized by changes for longer periods, which can be related to the dynamic balance established between the weathering processes and translocation of weathering products, as well as their solubility and precipitation. Depending on a relief, the systematic variability has shown shorter temporal range for concentrations of analyzed dissolved components in groundwater (in both the first and in the second structure of semivariograms). This relationship should be associated with a shorter duration of migration of rainwater to groundwater table by decreasing the thickness of the unsaturated zone with decreasing soil position on the slope. Values of the time correlation range obtained in this study indicate that on the one hand it is possible to monitor the concentrations of the components dissolved in the groundwater in longer time intervals but on the other hand the temporal intervals depend on well location in a catena.