User:EricDart/Müggelsee

Müggelsee
The Müggelsee, also known as the Großer Müggelsee, is a natural lake in the eastern suburbs of Berlin, the capital city of Germany. It is the largest of the Berlin lakes by area, with an area of 7.4 km², a length of 4.3 km

The lake is in the Berlin district of Treptow-Köpenick. The suburbs of Köpenick, Friedrichshagen, Rahnsdorf and a little section of Müggelheim border on the lake.

The lake itself has a mean depth of 4.9 meters (16.08 ft), and is 8 m deep at its deepest point. At its south end are hills called the 'Müggelberge', which are 115 m high; they were formed during the Pleistocene (as a kettle hole, remaining at Weichselian glaciation). On the so-called 'Kleiner Müggelberg', the much-visited and popular 'Müggelturm' (a tower) was built, the first one in 1889 (destroyed in a fire in 1958), and the current one in 1960/61. The tower offers extensive views over the lake and the forests against the Berlin skyline.

The River Spree flows into the lake via the smaller Kleiner Müggelsee, which is only 0.16 km² in area. The Friedrichshagen waterworks on the northern bank of the Müggelsee obtains most of its water from the lake. There are also numerous deep wells located near the banks, and are mainly fed by the bank filtrate and only to a small share by groundwater.

Etymology
The first uses of the word component "Müggel" are, according to Gerhard Schlimpert in the "Codex diplomaticus Brandenburgensis", in 1394 as "den Tyns in der Miggel" and in 1487 as "von der Miggelseh". The etymology remains unclear. The traditional derivative from Common Slavonic mogyla = "grave, grave hill, earth hill" is rejected by Schlimpert as not durable. A pre-Slavonic, Germanic origin from a Proto-Indo-European root is more probable: migh-, mighla = "fog, cloud": compare Dutch miggelen = "drizzle" belongs. Analyses say that the word component "heim" in the name was brought around 1750 by settlers from the Palatinate from their homeland Odernheim, according to Schlimpert.

Namesakes
In December 2013, a lake on the Saturnian moon Titan was officially named after Lake Müggelsee by the International Astronomical Union. That lake is composed of liquid methane and ethane, and is located at 84°26N and 203°30W on Titan's globe.

Formation
The Müggelsee was formed as a kettle lake during the Pleistocene era. The rock and sediments trapped in the ice, which can then be broken off as glacial till. In this glacial till there can be large chunks of ice which can then lead to lakes or ponds forming after they melt, such as what happened to the Müggelsee. It is also known to be a part of the Warsaw-Berlin Glacial Valley, meaning it was formed approximately 18,000 years ago. Along with this, the lake is considered to be a eutrophic lake, meaning that it has an excess of nutrients which cause large growth of plants and algae, resulting a low oxygen content. The oxygen concentration of Müggelsee is 13.5 mg/L.

Temperature
The Müggelsee is a polymictic lake, with it remaining mixed the majority of the year only stratifying occasionally. This is due to the constant flow of water through it from the Spree river, causing a retention time of about 42 days, as well as due to its large surface area, which exposes it to high levels of wind. Both factors along with its relative shallowness cause it to frequently go through periods of mixing with occasional short windows of stratification in the summer. In winter however, the Müggelsee does freeze over the winter where it becomes inversely stratified. Multiple studies have shown that the temperature of the Müggelsee has been steadily increasing in recent years. This increase in temperature is likely due to global warming. Climate change in the Berlin area has resulted in an overall increase in temperature by about 1.5 degrees Celsius. This increase in temperature has affected the Müggelsee a lot as it is a relatively shallow lake. The temperature of the lake is predicted to rise by about .1-.11 decrees Celsius every decade between the years 2006-2100 according to a study published in march 2019 by Tom Shatwell, Wim Thiery, and Georgiy Kirillin.

Nutrients
The Müggelsee is a hard-water lake, displaying high alkalinity and high levels of calcium. As well as this the Spree river carries in large amounts of nutrients. However in recent years there has been one of the few lakes in the world where it is experiencing a significant decrease in the amount of phosphorous and nitrogen pollution. This was likely due to numerous pieces of legislation being passed to decrease the runoff caused by wastewater and agriculture. The levels of specific nutrients in the lake are constantly shifting as well. In the summers between the years 1979-2016, the lake consistently displayed an excess of phosphorous in the water, but lower levels of nitrogen. While earlier in the year it displayed high levels of both nitrogen and phosphorous. This is likely due to snowmelt carrying excess nutrients into the river Spree, which then gets transferred into the Müggelsee.

Algal/phytoplankton blooms
The Müggelsee often goes through substantial algae blooms in both spring and summer, with summer blooms often being dominated by cyanobacteria. This is due to a mix of the warm temperatures and the high influx of nutrients from the Spree river. As well as this the higher temperatures in summer encourage the growth of cyanobacteria. The blooms have been shown to be potentially toxic to humans depending on the species of cyanobacteria as well. Microcystis, which release toxic chemicals into the water after they die, is the most common toxic cyanobactiria that can be found in the lake. The Müggelsee also experiences phytoplankton blooms, which oftentimes occur while the lake is still covered in a layer of ice but melting has started to occur. This may be due to the large influx of nutrients caused by melting snow and ice flowing into the Spree river, which then makes its way into the lake. These blooms will last until the lake reaches it's clear water phase in May.

Transparency
The transparency of the Müggelsee has been well documented over the past century, with measurements taken mostly by using a secchi disk, which is a round disk about 8 inches in diameter With a mean secchi depth of 1.45 meters in the early 1900's, though by 1978 the mean secchi depth had decresed to .58 meters. From this it was determined that the particulate material in the water by 1978. This can be be attributed to more sediments potentially being introduced through the Spree river and runoff, as well as algal and phytoplankton blooms. However by 2009 the secchi depth has rose up to about 1.2 meters. This is likely due to a decrease in agricultural and wastewater runoff entering the Spree River, meaning less nutrients were being carried into the lake.

The transperency of the lake also is subject to change depending on the time of year. Early in the year, while there are still large cases of algae/phytoplankton blooms, the transparency of the lake is severely decreased. As well as this the lake enters a "clear stage" once the phytoplankton have used up most of the nitrogen supplied from the snowmelt. A study published on April 14, 2016, noted that in winter there were low levels of chlorophyll A, which is used to measure the amount of phytoplankton in the water, the transparency of the water was high, with secchi depths of over 2 meters on average. In Spring during the phytoplankton blooms, the chlorophyll A levels appear high, while the transparency drops to a secchi depth of less than 1.3 meters. Then in may the lake enters it's clear water stage and the chlorophyll A levels drop while transparency rises back up to about 2 meters. Then phytoplankton blooms occur again around August, which decrease the transparency back down to below 1.3 meters

Research
Müggelsee has been and is the site of numerous long term research projects. Due to the relatively well documented data surrounding the lake, we are able to utilize that data looking back in order to observe long term changes to the environment. One of these studies used in order to quantify the stability of pelagic plankton populations, which showed a decrease in phytoplankton biomass of about -57% between the years 1981-2015. Müggelsee is also home to many ongoing studies tracking the amount of nutrients, temperature, and other biological changes. Many of these readings take place at a site called the Georg Mothes Automatic Research and Monitoring Station, which has been operating since the 1970's.