PATTERNS OF SOIL AND WETLAND SALINIZATION DUE TO DYNAMIC INTERACTION BETWEEN GRAVITY-DRIVEN AND OVERPRESSURED GROUNDWATER FLOW, DUNA-TISZA INTERFLUVE, HUNGARY

The Duna-Tisza Interfluve in Hungary has an agricultural economy but is plagued by severe problems of soil and wetland salinization. The study's objective was to determine the source of the salts and the controls and mechanism of their distribution. Based on regional hydrostratigraphic, hydraulic and hydrogeochemical evaluation, two groundwater flow-domains were identified: a gravity-driven meteoric “fresh” water domain and an over-pressured deeper domain of saline water. A schematic pattern of groundwater flow is proposed for the Interfluve region, the "Duna-Tisza Interfluve Hydrogeological Type Section". (Ca,Mg)-(HCO3)2-type meteoric fresh water infiltrates in the ridge region of the Interfluve and is hydraulically perched on the rising saline waters of the overpressured regime. The salts are found to originate mainly from the NaCl-type water of 10000-38000 mgL-1 TDS of the basement and deep-basin sediments. This water rises into a zone of NaHCO3-type waters of the higher Neogene sediments. The hydrodynamic interaction between the fresh and saline basinal waters seems adequately to explain the pattern of soil and wetland salinization as well as the contrasting chemistry between the wetlands of the low-lying Danube Valley and the elevated Ridge Region.