Ten Secrets from Hannover

Saltier than the North Sea: the Fösse

The Fösse is the “local stream” of the Linden district in Hannover—just eight kilometers long and a left tributary of the Leine, which flows right through the heart of Lower Saxony’s capital city. As small and short as it is, the Fösse packs a punch: with a salinity of nearly 100 grams per liter, it’s significantly saltier than the North Sea! But why is that?

Sweet and salty at the same time – very mysterious

The mystery slowly unfolds when you return to the source of the Fösse—which isn’t really a source at all, which in itself sounds quite mysterious. The Fösse is a small body of water in the Velberholz forest, located between the Seelze districts of Velber and Harenberg, just west of Hanover. It is formed by the confluence of small ditches in the forest, which are fed by the salty seepage water from the potash waste dumps in Empelde and Ronnenberg. In these mines, the salty deposits from shallow inland seas in the so-called Germanic Basin dating back over 250 million years were brought to the surface. The chloride in the tailings water from Bade and Salzgraben raises the salinity in the freshwater Fösse to sometimes nearly 100 grams (or 100,000 milligrams) per liter. "It is also interesting to compare this with the chloride content of the North Sea, which is around 19,000 mg/l. At the highest chloride concentration measured to date in the Fösse—91,500 mg/l—the stream was consequently 4.8 times saltier than the North Sea! As a result of the high chloride levels, the Fösse is biologically barren along most of its course. Apart from a few algae, no living organisms can be found downstream of the salt discharge. Instead, over time, salt-tolerant plants have established themselves in areas where the stream banks are not reinforced with concrete or wooden fascines. These species are otherwise characteristic of the salt marshes along the North Sea coast and are very rarely found inland." (Source: http://www.lebensraum-linden.de).

Beach asters and other North Sea plants – right in the heart of Hanover

Since the Fösse carries very little water, it often dries up during the warm summer months. The slow, quiet flow of the Fösse’s salty, brownish-green water through the landscape is particularly evident near the bridge on Woermannstraße in the Badenstedt neighborhood. From the wide walking and biking path through the greenery, the halophytes are easily recognizable—plants with thick, round leaves (in which they store salt) that are otherwise found only along the North Sea and that depend on the salty soil for their survival. In late summer, the purple-to-white-flowering sea aster (Aster tripolium) and, in autumn, the dark-red saltwort meadows along the Fösse catch the eye. The extent of the salt-tolerant flora along the Fösse is unique in Lower Saxony. Not far from the local community gardens is also a water treading facility, which was built in 2014 by the Badenstedt Citizens’ Association.

From nearby Benther Berg, the Fösse flows through the Fössetal green corridor to the freight bypass railway on the outskirts of Linden-Mitte. From there, it flows through a canal-like channel to Davenstedter Straße, passes under the Linden Harbor via a culvert, and reemerges above ground below the street Am Lindener Hafen. About 300 meters upstream from the Herrenhäuser Wehr, the Fösse finally flows into the Leine. Incidentally, the mysterious stream, with its name (derived from the Latin word “fossa” meaning “ditch”), also inspired the name of Fössestraße in the Linden-Mitte district of Hanover, as well as the Fössebad (opened in 1838 as a river swimming pool and reopened in 1960 as Germany’s first indoor and outdoor swimming pool) and the former Fössefeldschule school complex (renamed Albert-Schweitzer-Schule in 2011) in the Limmer district.