LIAG
 

Freshwater-Saltwater environments

Apparent resistivity map and vertical resistivity section map of coastal area at Bremerhaven-Cuxhaven (after B. Siemon, in BURVAL Working Group 2006). Blue colours mark low resistivities and thus show saltwater intrusions from North Sea and Elbe River.

Only 2.5% of the global water volume is freshwater. And 0.4 percent of this is in motion within the water cycle (evaporation, precipitation, subsurface/surface runoff). The remaining 99.6% are tied: 30.1% in deep seated aquifers, 69.5% in icecaps, glaciers, permanent snow or permafrost.

We need the fresh water to be alive. Salinisation of groundwater endangers our most important good. Main reasons for groundwater salinisation are:

 

  • Saltwater intrusion in coastal environments
  • Salt domes
  • increased mineralisation in arid areas

Additionally there may be anthropogenic reasons due to overfertilization and brownfields.

Due to the fact that the electrical conductivity depends strongly on mineralisation or salt concentration saltwater-freshwater systems are classical targets of geoelectrical or electromagnetic surveys. These resistivity methods respond to the electrical conductivity of the pore fluid that is increased by salt minerals. Water with chloride concentration higher than 250 mg/l is too salty. The drinking water standard needs an electrical conductivity of maximal 2500 μS/cm

Targets of geophysical surveying are, e.g., transition zone of freshwater-saltwater in coastal areas, submarine groundwater discharges, saltwater intrusions etc. The results may be the basis for studies on processes.