Lac de Sylans

The Lac de Sylans ( German Sylans Lake ) is located in the department of Ain ​​of the Rhône-Alpes region in France. It was created by a landslide and part of a gorge in the Jura mountains, which is transverse to the mountain ranges.

• 2.1 Flora and Fauna
• 2.2 Protection Status

Geography

The lake is located in the Jura transverse valley cluse de Nantua, which cuts through the anticlines of the Jura in the east-west direction, about 5 km to the east of Nantua. It covers a length of 2 km up the valley floor and is enclosed on the north and south sides by steep wooded slopes that rise up to 350 m in height. In the area of the lake cluse de Nantua is one of the narrowest points, so that the lake reaches only a constant width of 250 m. The lake is mostly to the municipality of Le Poizat, the few kilometers to the southeast, however, lies on the plateau Grande Montagne. A small piece from the western end of the lake belongs to the municipality of Les Neyrolles.

Due to its location on the watershed between Semine and Oignin the lake has only the stream Charix, however, considered as inflow is due to its location in a karst area of underground tributaries, which again increase the topographic catchment area of 30.7 km ². A special feature of the lake is the existence of two separate outflows. The seawater seeps on the west side in the loose rock of the rock aufstauenden leaving and comes as a source of Doye above Les Neyrolles reappear. The effected thereby discharge rate is approximately constant and placed in the precipitation poorer summer months a 4-5 m wide riparian strips dry. In wet periods, and especially in winter, this runoff is not sufficient and the excess seawater flows in addition on the east side above ground in the creek Combet. The outflow to Combet and the estuary of the Charix meet in the swamp area on the east side, so that the hydrology is not always clearly classify depending on water levels. Islands, the lake no.

Formation

For the Würm glaciation of the Rhone glacier formed in the cluse de Nantua one side tongue mitformte the on the ground a few hundred meters wide glaciated valley. However, the Lac de Sylans was only towards the end of the Middle Ages, as at the west end of the lake took a large rock fall.

Ecology

The average residence time of the water in the lake is given as 210 days, but the uncertainty of this estimate is high, due to the complex hydrology and the regular volume changes. In summer there is a significant thermal stratification with up to 23 ° C water temperature at the surface, a mixing with the layers below 6 m depth is, however, only in March after the ice instead of ( Meromiktisches waters).

The lake water is medium hard, with around 10 ° dH, due to the lime-rich catchment. The electrical conductivity at 350 ĩS / cm. The deposits in the lake consist predominantly of silt, ie of mineral sediments of very small particle size.

Flora and Fauna

The shore is forested in the area of ​​steep slopes, in the area of ​​preserved as a ruin former ice factories there lush vegetation. A swamp area is located at the eastern end of the lake. Found in the water several unicellular algal species: in winter, especially the dinoflagellates belonging to the genus Gymnodinium helveticum before, during each Sertularia much the kind Dinobryon increased during the summer and also represents a large proportion. Larger species of plants grow only on a small part of the lake area, and their diversity is also low. There are also observed mare's tail pondweed, milfoil Ähriges, Chara and the marshy, flat east bank. At the bottom of the lake also live pea shells.

Protection status

The Lac de Sylans is since 1909 a site classé, ie a conservation area. Due to the low population and absence of major agricultural land in the catchment area and the disposal of sewage road is little risk of pollution or eutrophication.

Economic Importance

On both sides of the lake extend essential road and rail links. On the north bank, the street department D1084, which runs from Bellegarde- sur -Valserine about Nantua to Pont- d'Ain, and the A40 motorway, the junction for Les Neyrolles is on the lake is located. In the area of the steep slope above the lake the highway runs on a stilt Viaduct, the Viaduc de Sylans. Along the narrow southern bank performs the railway Haut-Bugey line with TGV services between Geneva and Paris.

Due to its mountainous location shaded by steep slopes, the lake in season from November to March is frozen regularly. An entrepreneur from Nantua therefore founded in 1865, the ice plants of Sylans, reaping, Incorporation of, and deliver for cooling purposes to customers in the course of the rest of the year, the very pure natural ice in the winter. With the help of 1882 completed railway line, the ice plants supplied approximately 300,000 tons of ice per year to Paris. The Société des Glacières de Paris bought in 1885 the ice factories and built beside a lake, 150 m long and 12 m high office building made ​​of brick stone, which still dominates the lake panorama in ruins today. The progressive electrification and distribution of refrigerators dropped the demand for natural ice in the following decades, however, break again. In addition, severe mild winters from 1911 Eisgewinnung, so it was set in 1917 during the First World War.

Today, the lake, the water supply of Les Neyrolles safe.