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Aquaculture at sea and the decommissioning of offshore wind farms come with many opportunities and challenges. For the efficient development of future policy on these activities, it is essential that the priorities and concerns of the many stakeholders are heard and integrated in an open and transparent manner into a broad-based vision that policymakers can subsequently work with.

To address this, the Royal Belgian Institute of Natural Sciences launched two separate participatory trajectories on these themes on behalf of the Marine Environment Department of the Federal Public Service Public Health, Food Chain Safety and Environment and Minister for the North Sea, Vincent Van Quickenborne. More than 50 different organisations responded to this interactive cooperation initiative.

Steven Degraer (Royal Belgian Institute of Natural Sciences): “Getting stakeholders to talk to each other always yields surprising insights and this for all parties around the table. It is the way to get to know each other, share insights and look for a sustainable future for the sea together.”

The kick-off of both trajectories took place in Bruges on Tuesday 18 October 2022. Stakeholders met almost monthly, and also worked intersessionally on vision-building. During a closing event on Monday 15 May, also in Bruges, the resulting visions around aquaculture and decommissioning of offshore wind farms in the Belgian part of the North Sea were presented to the trajectories’ participants and the press.

Aquaculture

Key elements identified within the stakeholder consultation on marine aquaculture are:

Sustainable food production for our and future generations is the primary goal of aquaculture in the Belgian part of the North Sea. Various organisms are suitable for this purpose. First and foremost, oysters and mussels are considered, but also algae, whelks, scallops and other bivalves, crustaceans and fish. Aquaculture of jellyfish, sea cucumbers, sea urchins, sea grasses and even bacteria is also theoretically possible. To what extent combining the farming of different species (integrated multitrophic aquaculture) is possible our Belgian North Sea needs further investigation.

Other economic activities (such as fuel and cosmetics production, tourism) can be linked to aquaculture and thus play a role in eliminating residual flows.

Optimal use of available space is one of the main concerns. Potential spatial conflicts with other users of the sea were raised, as well as opportunities for multiple use of space.

Attention to the environment also scores very high. Here, there is not only concern about possible forms of negative impact, participants also see opportunities to combine aquaculture with nature conservation, nature restoration and coastal protection.

Basic and preconditions

Several conditions must be respected when looking for suitable sites and forms of aquaculture.

Important basic conditions are:

• To start with, it is important to understand in which locations the target species thrive. This varies between potential target species and depends on species-specific abiotic and biotic factors.
• Sustainable aquaculture should be extractive, meaning that no additional nutrients or drugs should be added. It should also not exceed the carrying capacity of the surrounding natural ecosystem.
• In nature reserves, aquaculture will no longer be allowed before the areas are in good conservation status, and then only with native species.
• Aquaculture products must comply with common food safety requirements.

Additional preconditions that should be pursued to the maximum extent possible relate to personal and marine traffic safety, multiple space use, social acceptability, environmental damage, cooperation, ecological footprint, engineering/technical aspects, socio-economics, legal and insurance aspects and broad governance context.

The future

A North Sea in good conservation status is a prerequisite to provide sufficient carrying capacity for aquaculture. To promote opportunities and mitigate concerns, well-designed licensing criteria must be established. Administrative obstacles and red tape must be removed. The development of a central monitoring and warning system and a pooled knowledge platform would offer many benefits. Targeted grants could help address knowledge gaps and develop opportunities.

In the next phase, additional data and map material will be collected to create an opportunity map for aquaculture in the Belgian part of the North Sea, linked to the predefined basic and boundary conditions. Taken together, these elements will form a solid basis for policy support.

Cooperation and coordination between the North Sea countries is also desirable, including in terms of drafting uniform European regulations.

Vincent Van Quickenborne, Minister for the North Sea: “The North Sea is a breeding ground for innovation. With no fewer than 53 partners, we have joined forces in recent months on two important themes. For instance, despite our small North Sea, we have a lot of space to do aquaculture. E.g. between the windmills. We are now mapping those areas. We are looking into species of which we can combine the cultivation. And we are looking for European money to invest in this.”

Decommissioning of offshore wind farms

The licences to operate Belgium’s already operational wind farms date back 10 to 15 years. The decommissioning of that first generation of wind turbines is now approaching. Just as the installation of these farms was pioneering work, their decommissioning will be too. Moreover, in the time that has passed, many questions arose about the phased decommissioning process in the period 2034-2047. On the one hand, new technologies are succeeding at lightning speed and, on the other, new insights are constantly emerging around the interaction between wind farms and biodiversity.

New technologies: New options for decommissioning offshore wind farms are being developed, with regard to techniques, materials and cost. For example, options for repurposing and recycling blades and ways to remove monopile foundations in their entirety from the ground are being explored.

Biodiversity: Monitoring the ecological effects of wind farms shows that additional biodiversity has been created in and around the offshore wind turbines, the so-called artificial reef effect. The new hard substrates underpin a rich underwater fauna of invertebrates, which in turn attracts various fish species, bird species and marine mammals.

Decommissioning options

To decommission offshore wind farm infrastructure, there are several theoretical options. The foundations can either be completely or partially removed or remain entirely on site. Erosion protection layers and cabling can also be removed or remain on site. The majority of the participants to the process of vision creation favoured complete removal of all man-made structures.

The naturally occurring and desirable fauna of dynamic sandy substrates is adapted to high dynamics, allowing it to withstand a temporary disturbance caused by decommissioning activities well and recover quickly. The new biodiversity created as a result of the artificial reef effect is not considered of such interest in a naturally dynamic sandy-bank ecosystem to be left untouched because it is a habitat that does not naturally occur at that site. Moreover, when decommissioning in the context of repowering, hard substrate will again be provided in the form of a new wind farm, so that those additional habitat, shelter and resting opportunities will recover in the short term and in phases.

Leaving some of the infrastructure in place could be useful for attaching structures for aquaculture, passive fishing or as a research base (sensors, testing new technologies, etc.), for example, but these functionalities could equally be envisaged for yet-to-be-built wind turbines.  In addition, retaining (part of) the monopiles and leaving erosion barriers and cables in place do not outweigh the disadvantages of insecurity and the missed opportunity to reuse materials.

In contrast, wind farm operators, who after all have to carry out and pay for decommissioning, are rightly concerned about whether it will be both feasible and affordable engineering-wise to completely remove a monopile. Also, removing the erosion protection, even if it is to be reused for the same purpose when repowering, is a costly and time-consuming activity. Thus, further research and consultations still appear necessary to identify the feasibility and the advantages and disadvantages of the alternative decommissioning scenarios (complete removal, partial removal or complete abandonment of wind farm infrastructure, including erosion protection layers). By starting this in time, with the vision process as the first component, we give time to the public and private partners involved to prepare.

Useful info for future wind farms

The findings from the participatory process also offer insights into how future wind farms can be optimally designed, taking into account the decommissioning phase. In particular, promoting circular use of materials offers sustainability opportunities.

The Princess Elisabeth zone contains zones of natural hard substrate, a low-dynamic habitat with high ecological value. Decommissioning activities will therefore have a greater impact here than on the dynamic sandy soils where the current wind farms are located. On the other hand, in the gravel beds of the Princess Elisabeth zone, many win-wins can be achieved by implanting artificial hard substrate such as wind turbines and erosion protection layers. Whereas in the first zone it is advised, for reasons of natural value, to remove everything when decommissioning, in the Princess Elisabeth zone it remains to be seen how to avoid disturbance of the gravel beds during decommissioning as much as possible, and how to preserve the natural value of the artificial hard substrate in the vicinity of the gravel beds as much as possible.

Vincent Van Quickenborne, Minister for the North Sea: “Our country is among the world leaders in offshore wind. Now we are going to have to decommission the first generation of offshore wind turbines within a few years. We are now figuring that out with all kinds of agencies and researchers. Because we also want to decommission in a sustainable way. By being a pioneer in this activity, we ensure that our companies will once again be world-class specialists.”

 

The final reports of the stakeholder projects ‘Aquaculture’ and ‘Decommissioning of offshore wind farms’ will be available for consultation from mid-June on the Marine Environment Service website, specifically in the ‘North Sea Publications’ section (Dutch – French).

In its new report ‘Marine mammals in Belgium in 2022’ (available in Dutch and French), the Royal Belgian Institute of Natural Sciences compiles the results of monitoring and scientific research on marine mammals in Belgium in 2022. Relatively few Harbour porpoises washed ashore, but numbers at sea were among the highest since counts began. The numbers of dead seals washed ashore follow an upward trend, although there were fewer in 2022 than in 2021. The probable birth of a young Harbour Seal in Nieuwpoort was a first for our country. Two Humpback whales, two groups of White-beaked dolphins and a Sowerby’s beaked whale are among the rarer species in the southern North Sea.

Which dead or dying marine mammals washed up on our beaches? Which causes of death could be identified? What are the trends of marine mammals in Belgium? How many seals did Sealife take in? Which rare species were observed? These are the questions to which one can find the answers in the latest marine mammal report, which focuses on the results from 2022.

Harbour porpoises

In 2022, 45 Harbour porpoises washed up on our beaches, the lowest number since 2004. Four of these stranded alive, but all died on the beach or during attempts to rescue them. One of the animals was pregnant.

However, the fact that relatively few Harbour porpoises washed ashore cannot be related to the numbers present at sea. Indeed, aerial surveys over the Belgian part of the North Sea in March and October resulted in estimates of over 11,000 and over 2,000 Harbour porpoises. The March number was the third highest number documented since surveys began in 2009. The highest number was over 18,000 in April 2018. Although Belgian waters are only part of the habitat of Southern North Sea Harbour porpoises, and numbers in Belgium can fluctuate widely, the results confirm a pattern already evident in previous years: our waters contain the largest numbers in spring, with a shift to the west – English waters – in summer and autumn.

What was striking in 2022 was that half of the strandings occurred between July and September, often involving juveniles and starved animals. In previous years, Harbour porpoises stranded mainly in March and April, the period with the highest numbers at sea, and bycatch in fishing was the main cause of death. In 2022, bycatch could only be identified in two cases, while six Harbour porpoises fell victim to predation by Grey seals. A number of Harbour porpoises were too decomposed to determine the cause of death.

Seals

With 54 seals washed ashore dead (18 Grey, 10 Common and 26 that could not be identified to species), 2022 was a quieter year than 2021, when 101 dead seals washed ashore. A large proportion of these appeared to be victims of fishing with passive gear. It seems unlikely that such fishing was conducted in a different way or in a different area in 2021 compared to previous years and 2022, so possibly the 2021 peak can be partly explained by different meteorological conditions in spring or an anomalous movement pattern of Grey seals after weaning in the English east coast colonies.

Nevertheless, 2022 involved the second highest number of dead seals in the time series. At least 14 of them died in fishing nets, all between January and May. At least one animal was killed by another seal. Many seals were too decomposed to determine the most likely cause of death.

12 Grey seals and three Harbour seals ended up in the shelter of Sealife Blankenberge in 2022. As in 2021, some young seals, both dead and alive, had noticeable injuries around the neck, no doubt caused by monofilament yarn from passive fishing gear.

A Harbour seal was probably born on the right bank of the IJzer estuary at Nieuwpoort: a first for our country. We found no other data on seal births in Belgium in the 20th or 21st century.

Rare Species

In 2022, two Humpback whales were seen in Belgian waters (May-June and December), and there were two sightings of groups of White-beaked Dolphins (June and December). The solitary Bottlenose dolphin, social towards humans, was still present in the border area with France. Also a dead Bottlenose dolphin washed ashore (October). This animal possibly died after a ship strike. In 2022, as was the case in 2020, a live Sowerby’s beaked whale washed ashore (July). This is a very rare species in the southern North Sea. The animal could be returned to the sea. A month later, very close to shore, a live, non-identified beaked whale was seen. A dead Fin whale drifted along the Belgian coast before finally washing up in the Netherlands (September-October).

Additional contributions

Boxed sections take a closer look at 30 years of ASCOBANS (Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas), a project to avoid collisions of ships with whales, the role of the North Seal Team in protecting seals and measures related to the avian flu virus, which also affected marine mammals in a number of places around the world in 2022.

All marine mammals are legally protected in Belgium. Monitoring of the populations and research into explanations for the observed trends, for which the Royal Belgian Institute of Natural Sciences was appointed as the responsible institute, is part of the implementation of the Royal Decree on the protection of species in marine areas under Belgian jurisdiction, whereby, among other things, the agreements made within the Coast Guard are followed. Research into the state of health and causes of death is also an obligation in international agreements, which moreover teaches us a lot about the state of the marine environment. However, the monitoring and scientific research on marine mammals are only possible thanks to the support of the local emergency and control services and the enthusiasm and willingness to report of many observers.

The report ‘Marine mammals in Belgium in 2022’ was produced with the cooperation of the Department of Veterinary Pathology of the University of Liège, the Faculty of Veterinary Medicine of the University of Ghent, Sealife Blankenberge and the North Seal Team.

For information on recent sightings of marine mammals in Belgium and instructions on what to do when stranded, please visit the website marinemammals.be. The annual marine mammal reports (available in Dutch and French) can also be consulted here.

In 2021, an article in Nature made world headlines because it equated the carbon released from seabed disturbance due to bottom trawling to the amount of CO2 generated by the global aviation industry. Now these conclusions are refuted by an article also published in the prestigious journal. The authors, including Sebastiaan van de Velde of the Royal Belgian Institute of Natural Sciences and the Université Libre de Bruxelles, fear that using exaggerated figures for bottom trawling will increase global CO2 emissions while reducing global food supply.

An article published today in Nature refutes the conclusions of an earlier paper by Sala et al on the amount of CO2 released from the seabed by bottom trawling. That article made world headlines when it was published in 2021 because it equated the carbon released from disturbance by bottom trawling to the amount of CO2 generated by the global aviation industry.

In the new paper, however, researchers show that the methodology used by Sala et al greatly overestimated carbon emissions. To calculate the amount of CO2 released by bottom disturbance from bottom trawling, the authors of the 2021 study modelled the amount of carbon that would be disturbed, assuming that most of this carbon would be converted to CO2.

However, most of the organic carbon in the seabed would decompose and be released as CO2 anyway, regardless of whether it is disturbed by bottom trawling. Only a very small proportion of seabed carbon potentially responds to disturbance by bottom fishing. The effect of bottom trawling on carbon storage in the ocean floor appears to be as much as 100 to 1,000 times smaller than that of global air transport, according to the new study.

“The authors of the original study focused their calculations on the ‘juicy’ and reactive organic carbon at the surface, which would be rapidly released by natural processes anyway, rather than on the aged and much less reactive carbon stored on the seabed,” explains Sebastiaan van de Velde, senior researcher at the Royal Belgian Institute of Natural Sciences and the Université Libre de Bruxelles, and second author of the study. “Since the most reactive carbon is rapidly converted into CO2 anyway, assuming it is affected by bottom trawling greatly inflates the estimated CO2 emissions.”

Unjustly reassured

There is no doubt that bottom trawling disrupts natural carbon fluxes and disturbs marine life on the ocean floor, but seabed carbon fluxes are very complex. The use of exaggerated figures is worrying as many governments and other actors propose to ban bottom trawling and use “carbon credits” to offset other activities. But when the carbon emissions from disturbing the seabed are overestimated by several orders of magnitude, we risk being unduly reassured by any ban on bottom trawling. In reality, this could divert efforts away from more efficient methods, while in the meantime increasing overall carbon emissions while decreasing global food supply.

“Refuting results of previous studies is part of the classical scientific process: one study presents a hypothesis, others challenge it with their own experiments, and that’s how we get closer to the truth,” van de Velde concludes.

What technologies are used and can potentially be used in the future for the monitoring and inspection of fisheries? What are the current and future developments in fisheries control? How does Belgium do it? What does the European Fisheries Control Agency (EFCA) do and how do other European Union coastguard partners conduct fisheries control? How does this work in practice? 

The use of evidence based upon innovative technologies in fisheries monitoring and inspection constituted the theme of this third workshop under the Belgian chairmanship of the ECGFF, the European Coast Guard Functions Forum which brings together coastguard authorities of several European countries to work on collaborative issues. The aim of the workshop was to share experiences and good practices within the European Union.

From Tuesday the 2nd of May till Thursday the 4th of May, delegations gathered in Bruges, and went on an excursion to the port of Ostend. In total, there were 119 participants, the majority of whom were physically present, while only a few attended online. Almost all member states of the ECGFF that have a coastline participated, comprising 22 member states.

Piet Pieters, attending chair of the ECGFF opened the workshop in Bruges with a bit of history: “During the Golden Age, Bruges was a thriving seaside trading hub, home to nations from several European countries. It is symbolic that we, as maritime nations, are forging new, forward-looking partnerships with the European Commission and with the specialised European Agencies precisely at this location. Furthermore, what is discussed here is relevant not only to fisheries control, but also to all other coast guard functions.”

During a first session, the Department of Agriculture and Fisheries explained the current and future possibilities on fisheries control and the use of evidence in Belgium. A video was also shown on Flemish fisheries control and on how the EFCA operates in European waters using their own vessel. The EFCA then gave an overview of existing technologies and their potential for evidence collection to support fisheries control. Other agencies (EMSA and Frontex) and participants also shared best practices.

In the afternoon, a visit was planned to some coastguard platforms in the port of Ostend. As such, the participants visited, among others, the Sirius, one of the vessels of the Agency Maritime Services and Coast (MDK), Flemish government organization VLOOT and the Ocean Protector, a vessel of the EFCA,  which all play a role in offshore surveillance and control of fisheries. Finally, they visited the Maritime Rescue Coordination Centre (MRCC), where they were given a presentation on incidents involving fishing vessels at sea.

On Thursday May 4th , the practical issues were discussed further. A panel discussion was organized on the use of evidence provided by new technologies. This last day was concluded with a debriefing of the exercise of the Ministry of Defense.

 

The Coast Guard is a unique Belgian organisation that pools and coordinates the expertise of 17 partners in the maritime sector to ensure safety and security at sea. Partners also include the Scientific Service ‘Management Unit of the Mathematical Model of the North Sea (MUMM)’, part of the Royal Belgian Institute of Natural Sciences (RBINS).

In 2022-2023, the Belgian Coast Guard chairs the European Coast Guard Functions Forum (ECGFF). Together with the European agencies FRONTEX, EMSA and EFCA, it will organise a number of workshops during the year. In cooperation with DG Mare of the European Commission, it will also organise a Cybersecurity Working Group and the summit taking place at the end of September 2023.

How does the Green Deal affect the operations of coast guard authorities from different European partners? The Green Deal is a package of policy initiatives launched by the European Commission which aims to make the European Union climate neutral by 2050. How can we make security and law enforcement in European waters as green and sustainable as possible? What opportunities does the Green Deal create for coast guard organisations? And what challenges does this pursuit of sustainability entail?  

These questions constituted the theme of the second workshop under the Belgian chairmanship of the ECGFF, the European Coast Guard Functions Forum, which brings together the coast guard authorities of several European countries to work on collaborative issues.

From Monday the 17th  till Wednesday the 19th of April, delegations gathered in the Portuguese capital Lisbon, where EMSA is headquartered. The European Maritime Safety Agency was established in 2002 to ensure a high, uniform and effective level of maritime safety, security, prevention of and response to pollution caused by ships.

The workshop kicked-off with a welcome speech by Nathalie Balcaen, Flemish president of the ECGFF. Ms Balcaen emphasized the commitment of the Belgian Coast Guard, which guards one of the shortest stretches of coastline in Europe but is at the same time partly responsible for one of the busiest shipping lanes in the world.

During a first session, information and expertise was mainly exchanged on the new legislation surrounding the Green Deal and on challenges and opportunities for maritime transport, i.e. using alternative energy sources to power ships and better monitoring and control of exhaust fumes.

The topic of marine pollution was also discussed, more specifically prevention activities to protect the environment and the deployment of resources in the event of a pollution incident.

How can the Coast Guard adequately respond to loss of cargo from ships, or fuel tank leaks? And most importantly, how can pollution, of any scope, simply be avoided?

A notable speaker on the first day was Mr. Carl Decaluwé, governor of the Belgian province of West Flanders. The governor is responsible for coordinating emergency response on the North Sea and chairs the Belgian Coast Guard’s consultation body.

The second day was largely dedicated to EMTER 2.0, the European Maritime Transport Environmental Report. The workshop looked ahead to the results of this new study by EMSA and the European Environment Agency (EEA), which will not be published until next year. The report is a follow-up to the first version which was published in 2021 and probes the far-reaching effects that maritime transport has on the environment. For instance, it zooms in on the effects of shipping on climate, air quality, marine fauna and flora and the health of European citizens.

During the closing session, Ms. Maja Markovčić Kostelac, Executive Director of EMSA, commended the Belgian Chairmanship of the ECGFF underlining the excellent cooperation that went into organising what was a highly informative and yet very practical workshop.

The next European workshop will once again take place on the Belgian coast. It starts on May 2nd  with the BELCOASTEX exercise, during which various security scenarios will be tested in an offshore wind farm. From 2 to 4 May, EFCA, the European Fisheries Control Agency, will take centre stage. At the end of May, delegations will meet in Brussels to discuss cyber security. Later this year, in September, the final conclusions of the workshops will be formulated during a closing event in Knokke, Belgium. After this, the Belgian presidency will be concluded and the chairmanship of the ECGFF will be passed on to Portugal.

The Coast Guard is a unique Belgian organisation that pools and coordinates the expertise of 17 partners in the maritime sector to ensure safety and security at sea. Partners also include the Scientific Service ‘Management Unit of the Mathematical Model of the North Sea (MUMM)’, part of the Royal Belgian Institute of Natural Sciences (RBINS).

In 2022-2023, the Belgian Coast Guard chairs the European Coast Guard Functions Forum (ECGFF). Together with the European agencies FRONTEX, EMSA and EFCA, it will organise a number of workshops during the year. In cooperation with DG Mare of the European Commission, it will also organise a Cybersecurity Working Group and the summit taking place at the end of September 2023.

Circular Low Trophic Aquaculture in Offshore Wind Farms

The new project ULTFARMS aims to revolutionize the application of Low-Trophic Aquaculture (LTA) systems through the integration of novel engineering, technical, ecological, and biological processes to optimize production in harsh offshore conditions, low-salinity environments, and within Offshore Wind Farms (OWFs). This will be achieved through the development of six Low-Trophic Aquaculture Pilots located in offshore wind farms across the North and Baltic Seas. The pilots will cover the entire value chain expertise for LTA production in OWFs and are to be situated in Belwind (Belgium), Borssele (the Netherlands), FINO2, FINO3 (Germany), Anholt and Samsø (Denmark).

Within ULTFARMS, the Marine Ecology and Management team (MARECO) of RBINS leads WP7 ‘Environmental Sustainability Assessment’ and participates in several other tasks, offering its expertise in marine ecology, advisory services about environmental licensing and cumulative effect assessments and management. RBINS will also substantially contribute to the Belgian pilot.

Integrated monitoring and management

ULTFARMS will bring together stakeholders from across the value chains of OWF and LTA to ensure that environmentally sound, low-carbon, and safe LTA products are produced from design to commercialization. New cultivation structures, grow-out systems, and eco-friendly design measures will be advanced through the project. Through integrated monitoring and management platforms such as the HiSea service platform and by drawing on existing open databases and operational forecasting systems such as CMEMS (Copernicus Marine Environment Monitoring Service) and SeaDATANET, the planning and operation of LTAs will be effectively supported through an enhanced technical service.

As such, ULTFARMS will offer scientifically sound services to aquaculture producers for monitoring and minimizing diseases and alien species, managing inputs, optimizing sustainable production, and demand management including risk analysis.

Legacy

The legacy of ULTFARMS will be a profitable, sustainable, and ecological production chain of low-trophic level species, such as seaweed and molluscs, in offshore wind farms located in the North Sea and Baltic Sea. Furthermore, the project will share lessons learned and innovations developed through comprehensive communication and dissemination activities, which will be underpinned by the active involvement of five Associate Regions throughout the project.

ULTFARMS is a 42 month project that started on January 1st, 2023, and ends on June 30th, 2026. It is led by Deltares, an independent institute for water and subsurface research based in the Netherlands. The project consortium consists of 25 partners from 9 different countries. The project is funded by the European Union’s Horizon Europe research and innovation programme under Grant Agreement No 101093888.

Rising sea levels are increasingly bringing nature-based solutions to the fore. The construction of dunes in front of the dike are an example of such a nature-based solution. These protect us from flooding, but also provide other ecosystem services such as a pleasant environment for recreation, increased biodiversity, reduced sand nuisance behind the dunes, etc.

However, these solutions themselves require a lot of sand, while sand resources in the North Sea are rapidly depleting. Moreover, sand extraction also has an impact on the marine ecosystem. The SUSANA project (Sustainable Use of SAnd in NAture-based solutions) will develop a coupled ecosystem services model to weigh up the pros and cons of a dune in front of the dike (dune-by-dike). This model will support the development of a long-term strategy for the sustainable use of sand in nature-based solutions. The project focuses on two aspects of sustainability: (1) the (re)use of lower-quality sandy material and (2) striving to reduce the impacts of sand extraction.

The specific research questions are:

• To what extent can alternative sand sources also provide the necessary ecosystem functions and services in a dune-by-dike?
• What is the impact of different sand extraction regimes on the ecosystem functions and services of the bottom ecosystem on the different sandbanks, and on the more distant valuable gravel beds?

Based on these research questions, a linked ecosystem services model will be developed, which will allow us to weigh up the advantages and disadvantages of constructing a dune-by-dike, and the sand extraction required to do so, respectively.

The fieldwork has already started. This video (RBINS/Vera Van Lancker) illustrates the work on board the RV Simon Stevin (VLIZ) during a campaign at sea in early March 2023: taking vibrocores where sediment samples were extracted from the bottom via drilling to a depth of 2.5m. For RBINS, the aim was to map dredge dumping areas as an alternative source area of sand. Dumping leaves mainly sandy material at the site as the fine material is washed out by currents. The study sites were mainly situated in the coastal zone. However, sand quality here is considerably lower than in the more seaward reclamation areas, but possibly sufficient for the construction of nature-based coastal protection such as dune-by-dike. At night, the seabed and upper subsurface layers were mapped using acoustic measurement techniques.

The SUSANA project started in February 2023, lasts for 3 years and is financially supported by VLAIO/The Blue Cluster.

The project team consists of the following partners: Universiteit Antwerpen (coordinator), Universiteit Gent, Katholieke Universiteit Leuven, ILVO (Research Institute for Agriculture, Fisheries and Food) and RBINS (Royal Belgian Institute of Natural Sciences).