LAKE DÜMMER
Germany

Objective: This study case will showcase the strategic implementation of previously scattered actions to effectively protect and restore Lake Dümmer using a nature-based approach.

Lake classification

Lake size (km2)

Medium: 15 km2

Average depth

Very Shallow. Greatest depth: 1,4 m; average depth: 1,1 m

Geology

Eastern half sandy substrate, western half on marsh.

Altitude

Low-altitude Lake (0 – 500 meters above sea level)

Trophic status

Eutrophic – Polytroph

Lake ecosystem Status

Biodiversity

NATURA 2000 network

Part of the EU-VSG Dümmer (No. 3415-401, 4.760 ha),
Part of FFH-Area Dümmer (No: 3415-301, 2.965 ha),
Part of a Ramsar-Habitat Dümmer (3.600 ha)

Presence and condition of Annex I habitats (Habitats Directive)

Presence and condition of Annex I habitats (Habitats Directive) 3150 – Natural eutrophic lakes with Magnopotamion or Hydrocharition vegetation (B). 6430 – Planar and montane to alpine moist tall herbaceous meadows (B) 6510 – Lean lowland meadows (Alopecurus pratensis, Sanguisorba officinalis) (C) 7140 – Transitional and oscillating grassland bogs (C) 91E0 – Floodplain forests with Alnus glutinosa and Fraxinus excelsior (Alno-padion, Alnion incanae, Salicion albae) (C), also FFH species: Cobitis taenia [Rock Biter] (C); Misgurnus fossilis [mud whip] (C); Lutra lutra [Otter] (C); Myotis dasycneme [pond bat] (C); Apium repens [creeping celery] (B)”””

Presence and population status of protected bird species (Birds Directive)

Presence and population status of protected bird species (Birds Directive) Number of bird species breed regularly in the area, incl.: Gadwall (Anas strepera), Common Teal (Anas crecca), Garganey (Anas querquedula), Shoveler (Anas clypeata), Common Pochard (Aythya ferina), Tufted duck (Anas fuligula), Quail (Cornix coturnix), Partridge (Perdix perdix), Little Grebe (Tachybaptus ruficollis), Great Crested Grebe (Podiceps cristatus), Black-necked grebe (Podiceps nigricollis), Cormorant (Phalacrocorax carbo), Bittern (Botaurus stellaris), White Stork (Ciconia ciconia)

Species richness and diversity of native flora

The following plant species are predominant:
Marsh lousewort (Pedicularis palustris), Broad-leaved orchid (Dactylorhiza majalis), Flesh-colored orchid (Dactylorhiza incarnata), Creeping celery (Helosciadium repens), Lung gentian (Gentiana pneumonanthe), Great rattletrap (Rhinanthus angustifolius).

Ecological status

Ecological status (WFD)

Poor Ecological Status

Conservation status

Conservation status (IUCN)

Habitat management area and Species management area —Category IV

Threat level

Threat level (IUCN Red List of Ecosystems)

Endangered (EN): High risk of collapse in the near future.

Pressures:

High nutrient load via the input from the catchment area of the tributary Hunte, especially through intensive agriculture, leading to algae dominance. Reed decline due to erosion, high unnatural water levels from spring to fall (artificial damming for tourism) and feeding by animals (nutria, muskrat, wild boars, geese). Reed canopy loss greatest on low marsh sites (in the western and southern halves of the lake). Insufficient regeneration possibilities for the reed beds due to lack of low water levels in summer. Endangered continued existence of the breeding colony of the Black Tern. Occasional blue-green algae bloom, turbidity of the lake, consequently low expression of underwater plants/floating leaf zones, consequently considerable change in the underwater fauna as well as in the food supply for protected waterbird species. The fish fauna is impoverished, various age classes of fish drop out. Sometimes an outbreak of cyanobacteria in hot years, causing prohibition for swimming.

Historical Data

Since 1993, Naturschutzring Dümmer staff has been recording annually the populations of breeding and resting birds.

Other data collected by the Dümmer nature conservation ring is the development of the reed zone and development/expression of the floating leaf zone.

Data from the state nature conservation administration (NLWKN – Niedersächsicher Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz): regular recording of fish fauna, chemical-physical parameters in the lake as well as in the Hunte since 2016, in a dense measuring network.

Environmental officer of the District Diepholz: regular recording of the chlorophyll content in the lake.

Local Policy and Governance Structure

Lake owner: State of Lower Saxony, domain administration

Responsible for conservation: UNB of LK Diepholz and NLWKN. Ecological Station Naturschutzring Dümmer works in coordination with the latter, with the responsibility for nature conservation.

Responsible municipalities: Lemförde joint municipality, Damme town, Bohmte municipality.

Local communities’ involvement in the lake’s management

Several actions to involve local people and farmers were deployed by the Association and bio-district.

Proposed set of Protection and
Restoration measures

Lead Implementing organization and stakeholders involved: Naturschutzring Dümmer

Protection of existing reed beds to improve ecosystem condition, protection against erosion and pollution.

Development of new reed beds to improve ecosystem condition and protect against erosion and pollution.

Protection and development of floating plant zone to improve ecosystem condition.

Monitoring of grazing damage of reed beds to identify the need for further P&R measures.

Awareness-raising and Stakeholder Engagement activities to improve environmental literacy and increase stakeholder engagement.