Coastal dune

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Rubjerg Knude shifting dune in Denmark (2004)

Coastal dunes are dunes that occur in humid and arid areas. The sand for this type of dune is brought in from the sea beach. If the sand dunes not influenced by vegetation, caused sickle dunes (Barchan), in areas with vegetation influence parabolic dunes .

Dune outline

Foredunes on Amrum
Brown dunes on Spiekeroog . On the now acidic soils, the crowberry covers the northern slopes of the dunes in large dark green carpets.
Sectional diagram through a gray dune

Dune formation takes place in several phases, whereby a dune, depending on the circumstances, does not reach every phase. They differ particularly in terms of the flora that colonize them, with different plant communities replacing each other over time. The first phases, which are strongly characterized by grass, are characterized by strong mechanical loads, during which, for example, sand repeatedly spills the plants.

Primary or pre-dune

The area between the flushing line and the dune belt is called the primary or pre- dune. It has a high moisture content, but is less salty and nutrient-rich than the rinsing hem. Here you can still find salt-tolerant plants such as rush couch grass ( Elymus farctus ), potash saltwort ( Salsola kali ), sea ​​mustard and chickweed .

White or heap dune

The white dune, also called secondary dune or heap dune, is often several meters high and consists of pure quartz sand from the primary dune. Here the first signs of soil formation can be seen, but it remains with a raw soil ( loose syrup ) with a low nutrient content. Therefore it is only covered with vegetation to 10-30%. Typical plants are beach grass , beach rye , felty butterbur and sea ​​thistle .

Gray dune

The flatter gray dune emerges from the white dune. Their slope is around 20%. The soil development is already advanced in the stage of Ah / C soil ( Regosol ) and thus the gray dune has the richest vegetation belt in the entire dune area. The area coverage here is up to 90%. Their color is caused by dead plant material, the pH value of a gray dune sinks from around pH 6 to 7 to pH 4 to 5 during its existence. Typical plants are sagebrush , potato rose , lichen and deciduous lichen , hawkweed , Silver grass , creeping willow , stonecrop and dune rose . If there is no grazing, shrubs such as crowberry and common heather can immigrate. The gray dune, together with the brown dune, is also known as the tertiary dune.

Brown dune

The soil formation of the brown dunes is determined by the poor sands and covered by a closed vegetation cover. After Regosol, the stage of a nutrient-poor brown earth is usually reached. The vegetation adds organic matter to the soil. In contrast to the younger white and gray dunes, the carbonate is largely washed out here. The progressive acidification of the soil under the influence of precipitation and humic acids causes podsolization of the soil. The soils themselves are then referred to as podsol . Typical plants and plant communities are natural Heide companies , crowberry, Polypody , heather , creep pasture and sea buckthorn . Do people by sods removed the top layers of soil until just before the groundwater at these types how can sundew and lycopodiella inundata settle.

Dune valleys

"Primary dune valleys" arise from the sandy beach through the formation of new dune walls, by which parts of the beach level are shielded from the sea, "secondary dune valleys" through the removal of dunes on the side facing away from the sea. These are mostly directly connected to the brown dunes or are located between the gray and brown dunes. Especially in secondary dune valleys, moisture often collects through capillary rising groundwater and rainwater, which in some of these dune valleys leads to the formation of small watercourses that carry water all year round. The ecological importance of these humid dune valleys in the immediate vicinity of dry locations lies in particular in the occurrence of a combination of species of flora and fauna that does not otherwise occur in this form. The species typical for such locations include the natterjack toad ( Bufo calamita ) and the endangered beachling ( Littorella uniflora ).

Shifting dune

Lontzkedüne : a shifting dune on the Polish Baltic coast

Shifting dunes have little or no vegetation on the surface and, driven by the wind, move at a speed of a few meters a year. Moving dunes have a slight gradient on the windward side, the windward side , while on the windward side, the lee side , the slope is generally rather steep. They can reach heights of up to a hundred meters. Existing landscapes, such as heathland, forests and lakes, which are in their direction of spread, are overlaid by them. On shifting dunes, the development of a dune can often be viewed in several stages at the same time. Well-known shifting dunes are located on the Baltic coast in the Slowinzischen National Park in Poland ( Lontzkedüne ) and on the French Atlantic coast near Arcachon ( Dune du Pyla ).

Human use and hazards

In many places, dunes protect the coast from storm surges , but shifting dunes also pose a risk as they threaten to overflow human settlements and facilities. To fix dunes, they are planted with beach grass, for example. In some regions, dunes are regularly used as grazing land. This prevents small shrubs from settling.

Dunes are often of great importance for tourism. On the European coasts, many dune landscapes are criss-crossed by a dense network of hiking trails and parking lots, so that breeding birds such as gulls and ducks are almost only found in special protected areas.

Individual evidence

  1. ^ A b c Neuhaus / Beinker / Bründel / Lange: Dunes on the west coast of Schleswig-Holstein . In: Federal Environment Agency and national park administrations of Lower Saxony Wadden Sea / Schleswig-Holstein Wadden Sea (ed.): Wadden Sea Environment Atlas . Vol. 1: North Frisian and Dithmarsches Wadden Sea . Eugen Ulmer, Stuttgart 1998/1999, ISBN 3-8001-3491-8 , pp. 92-93.
  2. a b Berndt Heydemann: New biological atlas. Wachholtz, Neumünster 1997, ISBN 3529054046 .

Web links

Commons : Coastal Dunes  - Collection of images, videos and audio files