Study region Central Pannonian Basin, Hungary. Study focus Critical Zone (CZ) Science
generally focuses on the soil and weathered bedrock in a few or tens of meters depth,
thus influence of deeper groundwater on the CZ is understudied. Here we aim to introduce
a hydrogeological methodology that can separate normal and abnormal pressure regimes
and determine the groundwater flow pattern to characterize the connection of different
groundwater flow systems to the CZ. Basin-scale evaluation of about 5500 measured
hydraulic data were carried out by p(z) and h(z) profiles, tomographic maps and hydraulic
cross sections. New hydrological insights for the Region Three flow domains were separated
and characterized. Namely, i) the uppermost topography-driven flow systems, which
penetrate only a few hundred meters, ii) a deep overpressured regime below 1600–2100
m depth, which drives fluids upward; and iii) a newly identified transition zone between
the former two, which gains its energy from overpressure dissipation and contains
non-renewable water resources. Topography-driven flow systems and discharge areas
of the transition zone, where its upwelling saline water contributes to surface salinization,
are parts of the CZ. Discharge areas of the transition zone cover about 50% of the
Great Hungarian Plain. The overpressured system can only influence the CZ through
the transition zone. The approach and methodology can be used in any terrestrial sedimentary
basin where a deep overpressured regime exists.
