Managed realignment is the landward relocation of flood infrastructure to re-establish tidal exchange on formerly reclaimed land. Managed realignment can be seen as a nature-based flood defence system that combines flood protection by the realigned dike (artificial) and restored saltmarshes (nature-based). So far, research on coastal managed realignment is primarily directed to saltmarsh restoration on formerly reclaimed land. This study focuses on the realigned dikes. The aim of this research is to characterize realigned dikes and to indicate the characteristics that offer opportunities for nature-based flood protection. We categorized 90 European coastal managed realignment projects into two realigned dike groups: (1) Newly built landward dikes and (2) Existing landward dikes of former multiple dike systems. The second group has two subcategories: (2a) Former hinterland dikes and (2b) Realignments within summer polders. For each group we present the realigned dike characteristics of a representative case study. We consider that the use of existing landward dikes or local construction material make realignment more sustainable. From a nature-based flood protection perspective, the presence of an artificial dike is ambiguous. Our results show that targeted and expected saltmarsh restoration at managed realignment does not necessarily result in a greener realigned dike design that suits for combined flood protection with restored saltmarshes. We recommend coastal managers to explicitly take combined flood protection into account in the realigned dike design and steer the topography of the realignment site to facilitate nature-based flood protection and promote surface elevation increase seaward of the realigned dike in response to sea level rise. This makes managed realignment a nature-based flood defence zone for now and for the future.
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This research addresses the question on how Delfzijl can take advantage of the dykes referred to recreational activities within the next five years. In order to investigate this problem statement, the elaboration was started with the definition of research questions and secondary research. Here, brochures, websites, books and other researches were used to gather significant information about Delfzijl. Next, quantitative and qualitative research methods were used in order to collect data and information about the different stakeholders, the current situation of the municipality and the expectations of the people concerning the future. Thus, a fieldtrip was done to interview stakeholders and to distribute questionnaires to the sample. Additionally, a benchmarking was done with the German city `Nessmersiel` in order to compare and discover development possibilities. The research outcome is that Delfzijl suffers from a decreasing population number, a low level of recreational attractiveness and lack of money. Many people claim that the dyke is a significant resource that should be used for recreational developments. Hereby, developments can be done on a small budget.
The research presented in this thesis has highlighted (bio)geochemical, hydrological, and wetland ecological processes that interact and enhance ecosystem development on wetlands built on fine sediment. A combination of greenhouse and laboratory experiments were conducted. Some measured data from these experiments formed important input for subsequent analysis in a modeling environment. The findings presented in Chapters 2-6 can be divided into four topics: 1) Plant–soil interactions in the terrestrial zone, 2) wetland–terrestrial processes influencing nutrient availability in the land–water zone, 3) effects of plants on sediment consolidation in the terrestrial zone, and 4) effects of bioturbation on nutrient availability in the aquatic zone. The next sections give a summary of the results for these four topics. The last section summarizes the recommendations formulated for the Marker Wadden project.
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The seaweed aquaculture sector, aimed at cultivation of macroalgal biomass to be converted into commercial applications, can be placed within a sustainable and circular economy framework. This bio-based sector has the potential to aid the European Union meet multiple EU Bioeconomy Strategy, EU Green Deal and Blue Growth Strategy objectives. Seaweeds play a crucial ecological role within the marine environment and provide several ecosystem services, from the take up of excess nutrients from surrounding seawater to oxygen production and potentially carbon sequestration. Sea lettuce, Ulva spp., is a green seaweed, growing wild in the Atlantic Ocean and North Sea. Sea lettuce has a high nutritional value and is a promising source for food, animal feed, cosmetics and more. Sea lettuce, when produced in controlled conditions like aquaculture, can supplement our diet with healthy and safe proteins, fibres and vitamins. However, at this moment, Sea lettuce is hardly exploited as resource because of its unfamiliarity but also lack of knowledge about its growth cycle, its interaction with microbiota and eventually, possible applications. Even, it is unknown which Ulva species are available for aquaculture (algaculture) and how these species can contribute to a sustainable aquaculture biomass production. The AQULVA project aims to investigate which Ulva species are available in the North Sea and Wadden Sea which can be utilised in onshore aquaculture production. Modern genomic, microbiomic and metabolomic profiling techniques alongside ecophysiological production research must reveal suitable Ulva selections with high nutritional value for sustainable onshore biomass production. Selected Ulva spp lines will be used for production of healthy and safe foods, anti-aging cosmetics and added value animal feed supplements for dairy farming. This applied research is in cooperation with a network of SME’s, Research Institutes and Universities of Applied Science and is liaised with EU initiatives like the EU-COST action “SeaWheat”.
For the general public harbour and grey seals are the symbol of the Wadden Sea. The Wadden Sea is an ideal environment for seals: sandbanks that fall dry at low tide are important for rest and for suckle pups. However, the total population of harbour seals has first stabilized and later decreased in recent years, while the annual number of pups born has increased, but the mechanisms underlying this mismatch remain unclear. Furthermore, the harbour seal population has declined since 2022, but the cause of this decline is also unknown. The objective of the proposed study is to increase our understanding of the mechanisms underlying the population trends of harbour seals currently observed in the Dutch Wadden Sea. The study will be carried out by a consortium, involving key players involved in seal conservation and research in the Netherlands. Furthermore, to ensure that the research is embedded in the international context, the Common Wadden Sea Secretariat is a partner in the consortium. The consortium partners have concluded that essential monitoring data on harbour seals is missing and therefore we propose to investigate and report on four themes: (1) mapping of governance, stakeholders and data landscape, (2) identifying mechanisms underlying the observed population numbers, by reviewing available evidence and exploring possible mechanisms, (3) evaluation and improvement of harbour seal monitoring and (4) communication and advice for governance. We will share our findings through reports, scientific papers, infographics, conference presentations, workshops, and proposed monitoring protocols. We will synthesize and communicate our findings targeting four specific groups: (1) the general public (2) the scientific community, (3) educational institutions, and finally (4) the ministry of Agriculture, Nature and Food Quality (LNV), providing them with advice on how to advance research, conservation and management of the harbour seal population in the Dutch Wadden Sea.
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