Improving coastal lagoon benefits under multiple pressures

Lead Author: DELTARES


The Wadden Sea is an international, highly productive estuarine area, and one of the largest coastal wetlands in the world. Situated abreast mainland Europe in the south-eastern portion of the North Sea, it borders Germany, the northern portion of the Netherlands, and western Denmark, thereby requiring tri-lateral cooperation in the management and protection of the system. This coastal area is a biodiversity hotspot due to its positioning as a convergence point of multiple domains, including terrestrial, fresh water, brackish and marine habitats. This multi-faceted combination allows for the support of a wide breadth of biota. The Wadden Sea is characterized by extensive tidal mud flats, saltmarshes, and deeper tidal creeks between the mainland and chain of islands which denote the outer boundary between the Wadden and North Sea. This mosaic of systems interacts dynamically due to wind, wave, tidal and riverine/runoff forcing functions, resulting in the creation of different types of coastlines. The common composition of such a coastline includes one or all of the following: i) a barrier coast with lido, barrier islands, mudflat systems and coastal lagoons, ii) deltaic systems and iii) bar-built and funnel-shaped estuaries. In the case of the Wadden Sea, all aspects are included to varying degrees.

The area has both UNESCO World Heritage and Natura 2000 status. It is approximately 500 km long with a surface area of around 9000 km2, a quarter of which is located within the Netherlands. Almost the entire region is submerged at high tide, and half the area (the mud flats where many birds feed) is exposed during low tide. As with many lagoonal and estuarine systems, the variety of habitats and high productivity lends itself to having a large biodiversity of invertebrates, fish, birds and marine mammals.

The high value ascribed to the Wadden Sea comes from its important regulatory and maintenance functions for the south-eastern coastal portion of the North Sea, its diverse aesthetic values, and the protection it offers against westerly storms to the German, northern Dutch, and western Danish coasts. The Wadden Sea is a nursery area for many fish species as well as a resting and fuelling station for a wide variety of wading birds. More than half of the juvenile plaice, a flatfish, population of the North Sea grow up in the area. Moreover, more than 10 million birds spend varying degrees of time in the region, often on migratory routes between nesting grounds near the North Pole to wintering sites as far south as Africa. This treasured combination of varied species and aesthetics draws a high volume of tourists in many forms, including but not limited to island visitors, game fisherman, boating and mudflat walking excursionists, and commercial operations. Commercial activities include industrial fishing for commercial fish and shellfish; recently aquaculture for shellfish has been introduced. One of the objectives of the application of protected area status to the Wadden Sea is to limit the degree of exploitation by the commercial shellfish industry whose high degree of pressure through mussel extraction has significantly impacted the system’s capacity to support the large volume of migratory birds.

The management goals of the Wadden Sea are primarily at the national level, but agreements have been made between all three countries which have stake in a portion of the system to have the policy and management developed at the trilateral level; see Note that this organizational body needs to be taken into account when addressing future management issues of the Wadden Sea.


Pressures and implications for ecosystem state/condition changes and their services

One of the most comprehensive natural assessment documents for the Wadden Sea is the Quality Status Report (QSR) Wadden Sea (2010 This QSR describes extensively the natural values of the area, its development and the pressures causing the changes in it. It describes the different pressures in detail and their impacts on various ecosystem elements. The main issues described in this report which have been designated as of importance and to be addressed are as follows:

  1. Mainland salt marshes and intertidal wetlands have been lost; management needs to restore the natural character of the artificial forelands.

  2. Many anthropogenic changes have been applied to the tidal areas. These changes have resulted in spatial shifts in erosion/sedimentation zones, oxygen deficiencies, loss of tidal flat area, and siltation of gullies. This process has been directly attributed to a reduction of biodiversity and therefore requires remediation and a reversion to more natural state of hydro- and morphodynamics.

    1. Deepened estuaries and gullies to allow for shipping traffic

    2. Damming and use of dikes

    3. Tidal pumping

  3. The eutrophication of dunes and problem of invading (species of) bushes and trees due to decreased grazing

  4. Decreased dynamics of back-barrier salt marshes which have been made static by dikes and dams leaving them vulnerable to eutrophication and hydrosere (the process of plant succession in shallow fresh water bodies, leading ultimately to drying of the water body and a forest type climax stage).

  5. The declining quality of both bird and seal habitats caused by human disturbance (e.g. fisheries, aquaculture, and recreational activities), preventing further growth of these populations.

  6. The scope of foraging habitats for birds and fish (i.e. intertidal flats and low dynamic shallow waters). Gas-exploitation, which has been causing sea-bed lowering, in conjunction with sea level rise, threatens benthic communities and therefore also food availability for higher trophic level organisms.

  7. Eutrophication and pollution introduction from rivers and overland runoff, while reduced, are still above what has been deemed as acceptable and target levels (external pressure).

  8. Littering has increased (external pressure).

  9. High fishing pressure in both the North and Wadden Seas impacts predatory fishes which act as regulatory components of the ecosystem (external pressure).

  10. Increased introduction of alien species (external pressure).

  11. Climate change (external pressure).

  12. Wind farms (external pressures).

  13. Recreational pressure, such as island visitors, game fishing, boating and mudflat walking.

  14. Aquaculture for shellfish.

  15. Transport to and from the mainland (i.e. ferries) causes noise disturbance and pollution and shipping lanes need to be dredged regularly?

The above issues have impacts on all the above-mentioned ecosystem services.


Policy and legal instruments, and management responses in the Wadden Sea

The natural capital and environmental properties of the Wadden Sea are protected under a variety of regulations. It is designated as a Natura2000 site (habitats and bird SAC and SPA), a RAMSAR site, a Water Framework Directive transitional water body, and a UNESCO world heritage site.

The Wadden Sea covers three national territories: the Netherlands, Germany and Denmark. In the Netherlands, national legislation is developed to cover this international legislation. Currently, the Wadden Sea is protected by the Dutch Nature Protection Act, the Flora and Fauna Act (Dutch implementation of the Birds and Habitats Directives), and the Water Act (Dutch implementation of i.a. the Water Framework Directive). Next to these laws, the Wadden Sea is further protected by several international and national agreements and policies (which are less strict than the above-mentioned Acts), such as the OSPAR convention, ASCOBANS (for the protection of small cetaceans), and the Bonn agreement (which covers i.a. the protection of harbour seals). Also, the Wadden Sea is part of the Dutch Ecological Network, whose objective is to ensure the free movement of species between the large water bodies in the Netherlands. Each protection framework comes with a set of management goals, assessment approaches and monitoring requirements. These management goals are integrated as much as possible. To this end, a Wadden Sea Management Council has been set up, with the aim of improving the efficiency of all different managers of the area. At the moment, a mix of management strategies exist for the Wadden Sea. These focus on tourism, economic development, and nature protection.

The natural goals of the Wadden Sea (see the Management plan under Natura 2000, in Dutch) currently utilize the ecosystem-based approach in the development of remediation and management plans. In regard to pressure management, strategies vary from the reversal of mainland land reclamation (summer polders) impacts to limiting fishing for blue mussels and mussel seed while increasing the growth of mussel seed on ropes. They also include decreasing the influence of sand extraction and dredging on shellfish and benthic communities, lowering nutrients and pollution (especially oil) introduction, and limiting the collection of cockles to hand raking only. Tourism is now moving towards a higher level of sustainability, due to the assignment of the Dutch and German Wadden Sea as a UNESCO site. Relatively new pressures, i.e. wind energy and alien species introduction need to be better managed. The on-going impact of gas-extraction under the Wadden Sea is now heavily under debate.

An emerging issue of great concern is that of climate change. As mentioned above, when compounded with the effects of subduction resulting from gas extraction, it is placing the functionality of the shallow low-dynamic regions at considerable risk. The intertidal zones and the salt marshes also risk becoming compromised as the depths increase leading to marsh flooding and intertidal become sub-tidal. Furthermore, the dredging of shipping lanes has been increasing, especially in the estuaries of the Weser, Elbe and Ems, thereby causing increased siltation and turbidity in these areas.

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