Chemical evolution of groundwater in the River Danube deposits in the southern part of the Pannonian Basin (Hungary)

Processes controlling the groundwater chemical composition were studied in the River Danube deposits, in the southeastern part of Hungary. PHREEQM, a combined geochemical and one-dimensional transport model and PHREEQE, NETPATH and WATEQF geochemical computer codes were used to simulate these processes. The main processes controlling water chemistry are equilibrium with calcite, undersaturation in dolomite and albite weathering in the recharge area, ion exchange along the flow path, and ion exchange and mixing with old water at the end of the flow path. Ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied. Isotopic data support the geochemical model. The groundwater ages, adjusted for the modeled C mass transfer range from 3300 to 20 200 a B.P. Cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred. This displacement is attributed to tectonic and paleoclimatic events at the end of the Pleistocene.