Hydrogeological overview map of Lower Saxony 1: 200 000 — Salination of groundwater (WMS service)

The map shows the possible groundwater salinisation on a scale of 1:200 000. Freshwater-filled aquifers can only be found in Lower Saxony up to a maximum depth of 300 m. Their occurrence is limited to those areas where continuous water exchange is carried out by infiltrating precipitation water (zone of active water exchange). Among them, an increasing salinisation of groundwater can be observed (zone of delayed water exchange). At greater depths, an area with largely stagnant groundwater joins. The close relationship between freshwater deposits and active water exchange makes groundwater dynamics a central criterion for assessing the usability of the aquifers as well as in the delimitation of groundwater bodies. The depth of the salted water, that is, the draught of active water exchange, is largely controlled by the hydraulic properties of the rock layers and the potential of the freshwater bodies passed through. As a result, it varies greatly. In large pre-flooding areas (e.g. Elbe, Weser, and All Soiling) where the hydrostatic pressure is abruptly degraded as a result of the overflow of large amounts of groundwater into the pre-floods, large-scale pressure gradients may occur that cause the penetration of deep salinated water to the near-surface groundwater area (inland salinisation). The salinisation areas in deep groundwater are often bound to the quaternary meltwater channels cut into the older subsoil. The depth of the salinisation is at a level where no aquifers are formed outside the gutters. Inland, about 400 km² are also to be classified as groundwater salinisation areas caused by a blueling processes on high-lying salt sticks (salt stick blueting, subrosion, cf. salt structures of northern Germany 1: 500 000, © BGR, 2008). On the North Sea coast, as a result of the general sea level rise after the last ice age, seawater has penetrated on a broad front into the domestic aquifers (coast salinisation), with the freshwater present in them being displaced. Affected by this type of groundwater salinisation is a stretch of up to 20 km wide, a total of 2 500 km² of coastline, which is thus largely for groundwater use. Only on the coastal islands have freshwater lenses formed under the dune areas by leaching precipitation, which allow for drinking water to a limited extent. In Lower Saxony, areas with a total area of approximately 6 500 km² are affected by groundwater salinisations, which make groundwater use difficult or impossible. For the demarcation of the areas of salinised groundwater, the results of water analyses, geoelectric probes and digestion drilling were evaluated using geophysical well measurements. A water is called salted when its chloride content exceeds 250 mg/l, which roughly corresponds to the human limit of taste. The map distinguishes in the looser rock whether the entire groundwater body is salted or whether salt water has only been found in a part of the groundwater. In solid rock, only near-surface salinisations, also in the area of salt stalks, are represented.