Nixseebecken

Location:	A7 exit Seesen(Harz), B243 48 km through Osterode, Herzberg and Bad Sachsa to Nüxei. At the turnoff to Tettenborn. (51.567234, 10.528365)
Open:	no restrictions. [2023]
Fee:	free. [2023]
Classification:	Polje. border Staßfurt Dolomit - Werra Anhydrit
Light:	n/a
Dimension:	Springwiese: Ar=2.5 ha. Valley: L=400 m, B=50 m. Nixsee: Ar=8 ha. Fitzmühlenspring: Y=20 l/s.
Guided tours:	self guided
Photography:	allowed
Accessibility:	yes
Bibliography:	Kuno Priesnitz (1969): Das Nixseebecken, ein Polje im Gipskarst des südwestlichen Harzvorlandes, in: Der Südharz - seine Geologie, seine Höhlen und Karsterscheinungen, Jh. Karst- u. Höhlenkunde, Heft 9, München, 1969. online
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Description

The Nixseebecken (Nix Lake Basin) is an exceptional geotope located just east of the village of Nüxei. It is a station on the Karstwanderweg (Karst Trail) and is called a Polje. This term comes from Slovenian and actually means quite simply field. In the Dinaric Karst, in the area of former Yugoslavia, karst areas are mostly bare karst, without soil and therefore not suitable for agriculture. Polje are wide basins between karstified regions that form a plain with soil suitable for agriculture, hence the name. From a geological point of view, however, a polje is a plain consisting of soft, non-karstable rock, which interrupts underground drainage. The water emerges from karst springs or river caves at one end, flows through the fertile plain as a stream and disappears again into the karst at the other end at gorge holes or ponors. In contrast to the Dinaric Karst, polje are practically unknown in Germany. Die geologischen Voraussetzungen für die Bildung von Polje sind nicht gegeben. So this geotope is something quite extraordinary, a form of karst that does normally not occur in Germany.

The Nixseebecken is a basin or depression consisting of the Springwiese (a meadow with springs) in the north, a valley about 400 m long and the artificially dammed Nixsee in the south. About 500 m north of the Springwiese, the Zehntgärtenbach stream disappears into the Große Trogsteinhöhle cave. The Springwiese is irregularly shaped, it is bordered by 30 to 60 degree steep slopes. In the northeast an outcrop of gypsum is karstified, the cliff face of this outcrop is called Kalkberg. A karst spring emerges here, called the Fitzmühlenspring, and several more are located in the meadow. The water in all those springs is the reappearing water of the Zehntgärtenbach plus water which rains on the surrounding hills.

The various watercourses join and flow southwards through the 400 m long and 50 m wide valley to the south into the Nixsee. Several springs in the meadow also rise here, whose water also flows into the small stream. The stream now flows into Nixsee, located in a 400 m x 200 m depression. At the eastern end of this basin is a ponor (swallow hole), originally the water disappeared underground at this point. But the Nixsee was dammed up by a dam in front of the ponor.

The entire depression of the Nixsee polje is located in a plain that has several sinkholes. Some of them are filled with water, the largest being the Weißensee. Very interesting is the fact that the water level of Lake Weissensee is 10 m higher than that of the ponor, although it is only 100 m away. This indicates that his water circulates in an independent underground water course.

The requirements for a polje are thus met, a karst area with underground drainage interrupted by a basin where the water emerges from springs at one end, flows through the Eben, and disappears into ponors at the other end. Unlike the Dinaric poljes, there is no non-soluble bedrock in the basin. There are two possibilities for the formation of the Nixsee polje:

Either it is a partially collapsed cave system, its still existing parts are the various spring caves and the ponor.
Or over time several sinkholes, like the Weissensee, grew together to form a big depresion.