Salt Marshes, Meadows and Coastal Zones
Historically, there has often been a wide belt of meadows and marshes along many of the Danish coasts. This has also been the case at Løgstør Bredning, where the coastal zone used to be dominated by a gradual transition from freshwater to salt meadows when getting closer to the coastline. The meadows were intersected by several streams that connected the surrounding agricultural areas to the Limfjord.
Today, a narrow belt of protected salt meadows still exists along the coast, and behind this belt lies a dike that protects the agricultural land behind it. Restoring the extensive meadow areas could be part of a nature restoration effort. Large, continuous meadow areas and the recreation of the natural hydrology, with the transition between saltwater and freshwater, would create an interesting and dynamic natural area.
Salt meadows are naturally open landscapes, as there are no larger salt-tolerant trees or shrubs in Denmark. They are shaped by the salinity of seawater and periodic flooding from sea or fjord. Salt meadows feature a substrate that varies from moist areas, such as coastal lakes and lagoons, to drier zones. Typically, salt meadows form a strip along the shoreline, lying between the sea and the more intensively managed inland landscape. Low-lying reed beds, salt meadows, and salt-tolerant grass communities regularly flooded by saltwater are collectively referred to as salt marshes.
Salt meadows are low-lying, saltwater-influenced areas covered with vegetation, typically found along sheltered fjord or sea coasts. The meadows are periodically flooded by saltwater and are often divided into distinct plant zones. These zones form as different plant species have adaptations to the natural gradient from salt-affected meadows near the coast to areas with fresher conditions further inland.
To maintain low-growing vegetation, coastal meadows must be either grazed or mowed, which helps sustain suitable habitats for wading birds. Without such management, salt meadows gradually transition into terrestrial swamps dominated by taller vegetation, such as common reed (Phragmites australis).
Salt meadows are the most widespread of Denmark’s protected habitat types. At the same time, Danish salt meadows represent a significant proportion of Europe’s salt meadows, giving Denmark a special responsibility to protect this habitat.
Salt marshes serve as habitats and foraging grounds for numerous wading birds, migratory birds, invertebrates, and fish. Establishing new salt marshes enhances biodiversity by creating improved living conditions for a wide variety of plants and animals.
Salt marshes also play a crucial role as buffers against climate effects. Globally, salt marshes accumulate significant amounts of carbon, storing atmospheric CO2 over the long term, which helps mitigate climate change and rising sea levels. Salt marshes stabilize shorelines and protect against erosion, storm surges, and (climate-related) flooding. Additionally, they are essential for nitrogen and phosphorus cycling, contributing to the reduction of eutrophication.
Salt marshes are found along sheltered coasts of fjords and shallow marine areas in most coastal regions of Denmark. However, salt marshes are absent along most of the Jutland west coast, except in the Wadden Sea area, where salt marshes with significant tidal influence are the dominant terrestrial natural habitat. Historically, Denmark had significantly more salt marshes, but coastal protection measures such as dikes and groynes have prevented and disrupted the periodic flooding. Combined with the use of salt meadows for agricultural purposes, this has led to the disappearance of a substantial portion of these habitats.
The restoration of salt meadows can be achieved by raising the water level so that, instead of drained and cultivable lands, wet meadows are created. These meadows will periodically be flooded while remaining, especially during the summer months, dry enough for grazing. At the same time, the coastal dikes, which currently prevent the intrusion of water from the fjord and sea, need to be wholly or partially removed so that saltwater can enter the areas. Depending on the terrain, this will create saltwater-influenced areas with varying water levels. In some places, the salt meadow will only be flooded during high water levels. In other areas, more or less permanent water bodies will form, such as coastal lakes without a direct connection to the fjord or lagoons that remain permanently connected to the water in the fjord.
The location of salt meadows and marshes at the transition between the marine and terrestrial environments, along with their dense vegetation, makes them function as a natural coastal defense. Restored salt marshes will therefore contribute to coastal protection and can replace traditional coastal defense methods, which often have negative and undesirable consequences for coastal nature. When high water levels hit the salt marsh, wave energy will be reduced, and water velocity will decrease. This mitigates erosion and slows down the wave energy that can affect infrastructure behind the marsh. Furthermore, a healthy salt marsh can typically regenerate quickly after storms due to its ability to trap and bind sediments and other suspended materials. Nature-based coastal protection, therefore, takes advantage of the fact that salt marshes, possibly combined with eelgrass meadows, stone reefs, and biogenic reefs, in shallow waters can reduce the undesirable effects of sea level rise and erosion.
Restoring salt marshes will also contribute to increased carbon storage. When the tide floods the salt marshes, water velocity is reduced through the network of leaves and stems created by the salt-tolerant vegetation. This attenuation of wave energy leads to increased deposition of organic material and sediment on the surface of the salt marsh. The recurring floods also contribute to low oxygen levels in the soil which slow down the decomposition of organic material, contributing to carbon sequestration.