Temporal variability in groundwater chemistry in the Great Hungarian Plain during the period 1975–1989

Abstract

Abstract In the southern part of the Great Hungarian Plain, chemical analyses of groundwater were performed during the period 1975–1989 in two water flow systems. Three types of temporal variations can be distinguished: a long term trend; a variation depending on sudden pressure decrease (both these types of variation can be seen in water hardness and iron concentration); and a regular fluctuation in COD and NH4 +. The first and second types occurred in both flow systems and are correlated with pressure depletion which in turn is reflected by water level decrease in wells. It was supposed that water with higher hardness and higher iron content moves from clayey layers to sand formations because of pressure depletion caused by withdrawal. Regular fluctuations of COD and NH4 + occurring only in the River Danube deposits were similar to the phenomenon of chemical oscillation but with different time and space scales between chemical and geochemical processes, the former having periods which are very long: 1.5...