O1_Coastal lagoon

Improving coastal lagoon benefits under multiple pressures

Lead Author: DELTARES
Contributors: Ghada El Serafy, Alex Ziemba, Sonja Wanke, Myra van der Meulen, Arjen Boon, Evelien van Eijsbergen
Editor: Asja Bernd (UBT)


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. 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) 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 European 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 and 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 fishermen, boating and mudflat walking excursionists, as well as 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 a stake in a portion of the system to have the policy and management developed at the trilateral level; see http://www.waddensea-secretariat.org/trilateral-cooperation/organisational-structure. 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 (http://www.waddensea-secretariat.org/management/publications/the-wadden-sea-quality-status-report-synthesis-report-2010), as well as two more recent reports in Dutch (Janssen, et al., 2017) and (Smit, Kooistra, Bakker, Rijpma, Hoogerduijn, & Hoeksema, 2016). 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 important 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 among others 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 exists 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 http://www.waddenzee.nl/fileadmin/content/Bestuur/pdf/Natura2000/docs_mrt/Doeluitwerking_Waddenzee__def_2dec14.pdf, 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 are also at risk of 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.

Developments within ECOPOTENTIAL

Within ECOPOTENTIAL, we use different approaches focused on modelling to improve the understanding of ongoing changes in the Dutch Wadden Sea and what management strategies may be suitable in response.

1)    Mind Maps and Models
We used Mind Maps to determine the critical variables required for monitoring and evaluating the Ecosystem Services (ESs) and their proxies defined in the scope of work. By developing and working through a Mind Map (Figure 1), we condensed our we summarised the overall understanding of the Protected Area (PA) and its inter-relation with Ecosystem Services. By doing so, it allowed selecting the necessary variables for the different ecological models, which can provide PA managers, scientists, and stakeholders, among others, with a better understanding of the driving forces and dynamic processes of the coastal system in question. Ecological models are able to provide this information in different spatial and temporal scales giving the possibility to analyze numerous management scenarios and their possible impacts on future ecological conditions.
However, the hydro-ecological modelling of tidal zones, estuaries and coastal ecosystems poses a particular challenge because of the fluctuations and interactions of the systems. We applied different models related to ecology, hydrodynamics and biogeochemistry. Ensemble modelling approaches were able to introduce and capture uncertainties arising from the input and forcing functions on the model, thereby portraying the reliability and variability within the modelling effort.
In any ecosystem, primary production is one of the main drivers and in a region like the Wadden Sea where there has been a steady decline of seagrass, other primary producers take on a bigger role to keep the whole system stable. One of the main primary producers in the Wadden Sea is the microphytobenthos, which consists of mostly single-celled organisms. Because data on microphytobenthos occurrence is scarce, we combined different types of data to test if it is possible to predict the microphytobenthos distribution in the Dutch Wadden Sea, based on their requirements. These included in-situ measurements, Earth Observation data from satellite missions like Landsat and MERIS, and the Wadden Sea modelling results. Additionally, we processed an algorithm with the following input variables: sediment grain size prediction and MERIS Products such as Total Suspended Matter (TSM), Chlorophyll-a (Chl-a) and Photosynthetically Active Radiation (PAR) (Figure 2).
Two main training models were derived from the microphytobenthos prediction algorithm and were then fed into two main training models (Figure 3). Although more extensive data is required to further validate this procedure, this alternative method has proven to be a viable technique in developing more non-invasive procedures to map microphytobenthos while maximizing the use of existing datasets.

2)    The Dynamic Bayesian Network
Both anthropogenic pressures and fluctuating natural conditions can pose a particular threat to the ecosystem of the Dutch Wadden Sea: they can interact with each other and, thus, create feedback loops or cumulative or cascading effects impacting the ecosystem more strongly than each pressure on its own.
Understanding those effects and how they develop over time is a crucial basis for sound decision-making. One way to obtain knowledge about them are Bayesian Networks. They can deal with environmental problems and decision making under uncertainty. They also help to understand pathways or relationships between variables. We applied a Dynamic Bayesian Network that can detect cumulative and cascading effects, as well as feedback loops and the evolution of variables over time. The model focused on the influential components of the Blue Mussel (Mytilus edulis), represented by different variables (Figure 4 and 5).
The outcome of this research was a functioning DBN that can detect whether effects occur and how they interact. While some limitations arose from data scarcity, which may be overcome in the future, cumulative effects were able to be detected. The network, therefore, can enable stakeholders, local populations and decision makers to become more aware of them and to make better and more appropriate future management decisions.

3)    The Ecosystem Services Serious Game
Lastly, in order to better understand Ecosystem Services in the Wadden Sea and how they are impacted by anthropogenic activities, we developed a serious game. Through a digital interface, players can explore how effective different measures to optimise Ecosystem Services for specific goals are and what uncertainty lies in the pathways to achieve such an optimisation. Such a game may facilitate discussions between stakeholders on the implementation of possible measures and their effects, as well as the difficulties in coming to agreements. We built the game from publicly available social and economic metadata from the Wadden Sea and an Ecosystem Services impact analysis on present and proposed anthropogenic to determine their potential or observed impact.
The research showed how Ecosystem Services concepts can be used to understand coastal and marine management issues. Current challenges are the differing significance of certain indicators and different effects of anthropogenic activities on different services that can lead to an unbalanced overall outcome. Nonetheless, a serious game is a suitable method to visualize how coastal and marine management issues relate to coastal and marine management. In the future, serious games that integrate Ecosystem Services of unique areas such as the Wadden Sea can develop into management tools for decision-makers, as well as educational tools for the general public.


Figure 1: The Wadden Sea is confined by a series of barrier islands which mark the border between the North Sea and the Wadden Sea. These islands provide the intertidal flats shelter from the strong erosive forces of North Sea storms and also key nesting and breeding grounds for many bird species. This 2011 aerial shot showcases the Frisian island of Terschelling. Credit: https://beeldbank.rws.nl, Rijkswaterstaat / Joop van Houdt

Figure 2: Map showing the study area within the country borders of The Netherlands highlighted in yellow. Zoomed-in area is the Dutch Wadden Sea. GIS layer taken from DIVA-GIS. Credit: Sara Pino Cobacho

Figure 3: Thousands of migratory birds and many different species rely on the Wadden Sea area. For some, this bountiful ecosystem and adjacent North Sea acts as a refuelling station for longer journeys, providing needed energy and nutrition to make extended migrations from equatorials to arctics. Others come specifically to this region to breed and raise their young in the safety of the dunes of the Wadden Isles, feeding on cockles, and other intertidal staples. Credit: Jan van der Kam / CWSS

Figure 4: Snippet of the whole Dutch Wadden Sea Mind Map focusing on the tidal flats and their Ecosystem Services according to the CICES classification

Figure 5: Different inputs such as sediment grain size prediction, TSM, Chl-a and PAR

Figure 6: MPB training map from integration of sediment grain size map derived from a Landsat image and TSM, Chl-a and PAR derived from MERIS in May 2004 (left) and August 2004 (right)

Figure 7: Conceptual Dynamic Bayesian Network. The dotted blue links are time delay links that are used to enable a feedback loop in the network. Temporary variables occurring in two time slices of the DBN are (blue frame): Turbidity; Primary Production; Food Competition, Food Availability and Blue Mussels. The variables are grouped into natural and climate conditions, maintenance, fishery and water quality. These represent the natural conditions and anthropogenic pressures which are the most influencing factors for Blue Mussels.

Figure 8: The developed DBN depicting various anthropogenic pressures (e.g. tourism, chemical pollution) and natural conditions (e.g. nutrient load, wind, water temperature) affecting the blue mussel abundance in the Dutch Wadden Sea

Figure 9: Alpha version of the Ecosystem Services Serious Game

Figure 10: Many birds make use of the daily tidal cycle and scavenge the mudflats and exposed shorelines at low tide to collect tasty morsels including cockles, lugworms, mussels, and more. Here we see a group of waders poking through the shallow waters in search of a meal. Credit: https://beeldbank.rws.nl, Rijkswaterstaat / Rob Jungcurt

Figure 11: With its long tail and legs the black-tailed Godwit if well-adapted to searching for food in the mudflats. Credit: Bo L. Christiansen

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Smit, T., Kooistra, C., Bakker, J., Rijpma, J., Hoogerduijn, G., & Hoeksema, R. (2016). Wadden in beeld: Signalen vanuit het beheer.

ECOPOTENTIAL-related references
Guerra C.A., Pendleton L, Drakou E.G., Proença V., Appeltans W., Domingos T., Geller G., Giamberini A., Gill M., Hummel H., Imperio S., McGeoch M., Provenzale A., Serral I., Stritih A., Turak E., Vihervaara P., Ziemba A., Pereira H.M., 2019. Finding the essential: Improving conservation monitoring across scales, Global Ecology and Conservation, 18, e00601, https://doi.org/10.1016/j.gecco.2019.e00601.
Pasetto D., Arenas-Castro S., Bustamante J., Casagrandi R., Chrysoulakis N., Cord A. F., Dittrich A., Domingo-Marimon C., El Serafy G., Karnieli A., Kordelas G. A., Ioannis M., Lorenzo M., Monteiro A., Palazzi E., Poursanidis D., Rinaldo, A., Terzago S., Ziemba, A., Ziv G., 2018. Integration of satellite remote sensing data in ecosystem modelling at local scales: Practices and trends. Methods in Ecology and Evolution, 9(8), 1810-1821. Special issue Improving biodiversity monitoring using satellite remote sensing. https://doi.org/10.1111/2041-210X.13018.
Spinosa A, Ziemba A., Saponieri A., Navarro-Sanchez V.D., Damiani L, El Serafy G., 2018. Automatic Extraction of Shoreline from Satellite Images: a new approach. 2018 IEEE International Workshop on Metrology for the Sea; Learning to Measure Sea Health Parameters (MetroSea), pp. 33-38. IEEE. https://doi.org/10.1109/MetroSea.2018.8657864

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 641762.

Last update: March 2020