Big Sea (district of Diepholz)

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Great Sea Nature Reserve

IUCN Category IV - Habitat / Species Management Area

Big Sea (district of Diepholz)

Big Sea (district of Diepholz)

location Southeast of Barnstorf in Lower Saxony Diepholz
surface 24.6 ha
Identifier NSG HA 012
WDPA ID 81774
Geographical location 52 ° 39 '  N , 8 ° 34'  E Coordinates: 52 ° 38 '59 "  N , 8 ° 34' 22"  E
Great Sea (District of Diepholz) (Lower Saxony)
Big Sea (district of Diepholz)
Sea level from 35 m to 37 m
Setup date 02/28/1942
administration NLWKN

The Great Sea is a nature reserve in the Lower Saxon municipality of Eydelstedt in the district of Diepholz about 1 km northeast of the Holte farmers in the Donstorf district. It lies between Diepholz and Sulingen west of the Wietingsmoors in the Diepholzer Moorniederung . The nature reserve with the registration number NSG HA 012 is 24.6 hectares and includes the lake with the surrounding shore. The core area is the eponymous lake "Großes Meer" (also: "Holter Meer"). The area is one of the oldest nature reserves in Northern Germany and has been under nature protection since February 28, 1942. In places it borders on the protected landscape area "Environment of the Great Sea". The owner of the water is the municipality of Eydelstedt , the responsible lower nature conservation authority is the district of Diepholz .

The great sea

Emergence

The "Great Sea" is likely to be a relic of the Ice Age. It was probably formed 14,000 years ago as a “dead ice hole” in the soft ice age valley sands. This is supported by the surrounding 2 m thick yellow drifting sand deposit, while the rest of the lake area consists of river sands. Nearby to the northeast is the similarly created “ Small Sea ”, which has silted up in the meantime.

Area, catchment area and use

Today's open water area of ​​the “Great Sea” is 11.2 hectares, but it used to be much larger (1958: 16.7 hectares). The causes are presumably the lowering of the groundwater level in the 1960s, since the decline in water surface has essentially stagnated since around 1970. The superficial catchment area of ​​the “Great Sea” roughly corresponds to the surrounding network of roads and has an area of ​​approx. 47.3 hectares. This means that the lake has a relatively large catchment area compared to its surface or its volume, which means that the lake surroundings have a relatively large influence on the water quality. Most of the catchment area is used intensively for agriculture. Furthermore, extensive grassland use takes place in the vicinity of the water body. The lake is a traditional recreational area and is mainly used by locals for swimming, hiking or bird watching. The Barnstorf fishing association uses the “Great Sea” as fishing waters.

Morphometry

The "Great Sea" is a shallow lake with an average water depth of 1.09 m. The deepest areas with a maximum water depth of 1.55 m are about 70 m from the east bank. The lake volume is calculated at around 120,000 m³. The shallow depth does not allow stable temperature stratification, so that it is a polymictic lake . The “Great Sea” is strongly influenced by groundwater. The underground inflow comes mainly from the east, the outflow towards the west to the “ Wagenfelder Aue ”. In the summer months, the water level of the lake is mainly influenced by evaporation losses and the release to the groundwater. Therefore, the lake shows seasonal water level fluctuations of 0.2 to 0.3 m, with longer periods of drought even up to 0.8 m. The lake receives additional water supply from rainwater (around 5500 m³ per year) and an above-ground inflow from the catchment area to the east. The “Great Sea” naturally has no surface runoff. In the course of amelioration measures , however, an artificial passage was created on the south side of the lake so that, especially in spring, there can be a temporary drainage via the “Otternriede” into the “ Wagenfelder Aue ”. The bed of the river consists mainly of glacial drift sands. Today, however, the lake bed is covered over a large area by an average layer of mud of 1.14 m, which can reach a maximum thickness of more than 2.85 m. The sludge volume is calculated at around 107,000 m³.

Shore structure and trophy

The shore of the "Great Sea" is slightly egg-shaped, without large bays and has a length of 1600 m. The east bank falls above the water level, initially steeply (former shoreline) and then only gently. There is a great variety of structures on this bank. The much narrower west bank, which slopes like a funnel towards the lake, is less structured. High nutrient inputs from the surrounding intensively used agricultural areas lead to severe eutrophication of the “Great Sea”. Eutrophication leads to the fact that the original macrophyte- dominated lake condition with high visibility has shifted to a plankton-dominated condition with very low visibility. A zone of submerged aquatic plants is missing in the entire water today due to the severe turbidity. The current trophic status is polytrophic . Overall, species declines due to eutrophication have been recorded, the increase in biomass in the lake leads to an increased sedimentation rate and accelerated silting.

literature

  • Kurt Pfaffenberg (1941): The Great Sea near Holte (report)
  • M. Mauritz (2010): Development and current situation of the vegetation and site conditions of the NSG Großes Meer (district of Diepholz) . B.Sc. thesis at the University of Bremen.
  • F. Müller (2018): The hydrochemical characterization of groundwater and surface water near the Great Sea . B.Sc. thesis, Institute for Biology and Environmental Sciences, University of Oldenburg.
  • L. Otte (2018): Interactions between groundwater and surface water at the Great Sea near Holte . B.Sc. thesis, Institute for Biology and Environmental Sciences, University of Oldenburg.

Web links

Commons : Great Sea Nature Reserve  - Collection of images, videos and audio files