Arendsee (lake)

The Arendsee is a roundish - oval, sold loose lake in the region Altmark in northern Saxony-Anhalt. With over five square kilometers of water area is the largest natural lake in the state, with around 50 meters at the same time one of the deepest lakes in Northern Germany (see also: List of waters in Saxony -Anhalt). Its origin goes to multiple break-ins of the subsurface, most recently in the 17th century, back.

Geography

Location and dimensions

On the southern shore lies the city of Arendsee; on the northwest shore the village Schrampe. Further afield, among others, the towns of Salzwedel and are Lüchow (Wendland). The lake has an area of almost 514 hectares at an east-west extent of up to 3.3 kilometers and a north-south width of two kilometers. The average depth is about 29 meters, the maximum is around 50 (51 ) meters depth. The profile can be characterized as a trough - with relatively steep edge slopes and a very broad, more or less flat depth zone ( profundal ) in the range between 40 and 50 meters. The water level is 23.3 m above sea level. NN; the lowest point of the ground is thus situates around 27 meters below sea level.

Formation

The Arendsee differs in its genesis by the majority of the lakes of the north German lowlands, which are primarily of glacial or periglacial origin. It is located just above the "Dom " ( diapir ) of a salt dome. By the groundwater it came to Ablaugung the salts and subsequently to several burglaries of rock salt formations and lying on the salt overburden. The last time this happened even in historical times, proven in the years 822 and 1685, the waters shall be classified as water-filled sinkhole ( " Seefall " ) or collapse doline, Subrosionssee or Einbruchsee classified ( see for example: Rudow lake). Thereby applies in addition to the Zwischenahner sea ​​as the largest of its kind in Northern Germany. In the preliminary final collapse in 1685, the mill of the village sank into the water and the surface of the lake is said to have increased abruptly to 20 acres. After the affected Müller Arend lake and place have been renamed, it maintains a legend. However, it gave the name Arendsee already much earlier, he was mentioned as " Arnseo " in the annals of the Frankish Empire in connection with the collapse in 822.

More Description

On the western, southern and eastern shores of the subsoil profile falls seaward from quite steep and soon reached the depth contour of 20 meters. Exist only on the north side more extensive areas of shallow water, so that could establish extensive reed beds of reeds, cattails and bulrushes Schmalblättrigem here. The sediments on the lake bottom are made up of so-called marl, mud and sand. Four superficial flows should not be present; but these are very small in relation to the lake volume. The only apparent drainage is a narrow, temporary water-bearing stitch ditch on the northwest shore, the (later " Lüchower Landgraben " ) leads to " Landgraben ". In this - artificial - way of actually dischargeless Arendsee is connected via the Jeetzel indirectly to the Elbe. On the shore close predominantly forest land from black alder, oak and pine trees, as well as residential areas including many weekend home land, in the north, some agricultural land. A trip around the lake on a mostly quite close to the shore hiking and cycling trail includes ten kilometers of track.

Landscape protection

The Arendsee situated within the conservation area ( LSG ) Arend. Here, the lake with 514 acres represents approximately 77.5 percent of the area of the LSG. The remaining 22.5 percent is a narrow riparian strips around the waters. The south adjacent town of Arendsee ( Altmark) not part of the LSG.

Water quality

The Federal Environment Ministry gives a total volume of 147 million cubic meters (equivalent to 147 billion liters ) of water to and qualifies the Arendsee here as nutrient- rich or - loaded ( eutrophic ), in particular with a significantly high total phosphorus content. ( Called to be about 88 g / l as an annual average for 2005, or even about 200 μgP / l at last rather still an upward trend. ) The statement of an exceptionally good water quality for which the Arendsee has been praised in the first half of the 20th century ( "Pearl of the Altmark ", " blue eye Altmark " ), so for several decades into perspective. Although depending on the season is to be found with sight depths of sometimes more than four meters in fairly clear water; but it can also take a lot of water turbidity or a streak - to flaky greenish surface film due to blue-green algae blooms, which are promoted by the high phosphorus and nitrogen content. The cause of the nutrient load, among other discharges of untreated sewage are the municipalities as well as a dairy in the 1950s and 1960s - a practice that should have been abandoned until 1970. More items go back to the cottages or holiday home residents and bathers. Likewise, the high number of migratory birds and resting migratory birds is mentioned in this context, however. Thus, up to 35,000 Nordic Wild Geese at Arendsee hibernate and leave several tons of feces there. A overstocking with edible fish, especially vendace, which deplete the water- purifying zooplankton excessively is discussed. Recent studies, however, indicate rather on the groundwater inflow as well as on the channel system of the city Arendsee as the main source of phosphate.

The mid- 1970s and mid -1990s, there were large-scale experiments a Seesanierung. 1976 Deep drainage was installed and in 1995 rearrangements were made by located in the northern part marl sediments, to cover sludge and biomass in other places. Later studies revealed, however, that thus the phosphorus cycle, contrary to expectations not sustainable positive, that is P- lowering could be affected.

That the hydrologically relatively " isolated" Arendsee with more than 60 (100 ) years, has an extremely long replacement time of its water body makes it difficult to short-term improvement of the nutritional situation particularly. The biogeochemical cycles in the lake are primarily determined by internal processes. The particularly high during the spring circulation phosphorus levels are in the early summer by growing phytoplankton ( algae) consumed until their population collapses, a short clear-water phase occurs and then nitrogen-fixing cyanobacteria ( " blue-green algae " ) come to development. Towards the end of summer stagnation zone below the depth of 40 meters is almost free of oxygen. During the summer months also particularly high ( alkaline, alkaline ) pH values ​​of phased to about pH 10 are detected.

Especially, even under the pressure of the EU Water Framework Directive, which requires the production of a good ecological status for all water bodies larger 2015, is currently being discussed again amplified through rehabilitation options. Favorited is obviously the introduction of 6500 tons polyaluminumchloride, which is to bring about a chemical Nährstoffausfällung. Because of the potential environmental impacts of this measure, however, is not without controversy. Hunting officials are also calling for a relaxation of the ban on shooting wild geese, which are even referred to by some as " the main cause " of the blue-green algae problem. Even after the natural staying away many geese in recent years - this haunting now many newly formed mining lakes - the situation has improved but not recognizable. In preparation for a possible Seesanierung in the coming years are currently (2010, 2011) from Berlin's Leibniz Institute of Freshwater Ecology water chemical analyzes carried out, especially some potentially contaminated with manure and fertilizer inflows are the focus.

The quality as bathing, meanwhile, is " very good", the guideline values ​​of microbial parameters was used in the previous year as a criterion. Examines this was the burden of intestinal bacteria such as intestinal enterococci and Escherichia coli. Possible incompatibility reactions by contact and ingestion of " blue-green algae " are not included in this review.

Use

The Arendsee is used by tourists especially. He serves as bathing holiday and leisure days. Especially at the time of the GDR was the holiday on Arendsee popular as a substitute for a seaside holiday.

On the northeastern edge of the city Arendsee is a large beach with Seetribüne pier on which, for example, films are shown. The lake is navigable by sailing dinghies and other non-motorized boats. Since 1991 a paddle steamer modeled after Queen Arendsee runs in the summer months as a tour boat on the lake. Here, find the scheduled trips from Arendsee circular instead of counterclockwise. The use of the lake with another motor boats has been banned since 1969. In addition, the lake is used for windsurfing and fishing. Not far from the city Arendsee an eleven -meter-long former NVA patrol boat was sunk in Arendsee on 7 October 2006. It is about 16 meters deep divers and serves as a target.

Fisherman catching addition to other freshwater fish species vendace.

Others

The Arendsee is part of the Nature Area main unit group " Wendland and Altmark " and this forms the southeastern completion of the subunit " Lüchower lowlands ". Geographically, he is racing area bird hatching and regional importance, among others, as well.

Culture Historically various underwater archaeological finds are worth mentioning in particular a Neolithic fish fence and a medieval oak barge, a kind of barge (see links).

On the south shore of the lake is the Gustaf - nail area.