Forschungszentrum Küste

The European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System) operates a global-scale monitoring system for atmospheric trace gases, aerosols and clouds utilising the existing global civil aircraft. This new monitoring infrastructure builds on the heritage of the former research projects MOZAIC (Measurement of Ozone and Water Vapour on Airbus In-service Aircraft) and CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container). CARIBIC continues within IAGOS and acts as an important airborne measurement reference standard within the wider IAGOS fleet. IAGOS is a major contributor to the in-situ component of the Copernicus Atmosphere Monitoring Service (CAMS), the successor to the Global Monitoring for the Environment and Security – Atmospheric Service, and is providing data for users in science, weather services and atmospherically relevant policy. IAGOS is unique in collecting regular in-situ observations of reactive gases, greenhouse gases and aerosol concentrations in the upper troposphere and lowermost stratosphere (UTLS) at high spatial resolution. It also provides routine vertical profiles of these species in the troposphere over continental sites or regions, many of which are undersampled by other networks or sampling studies, particularly in Africa, Southeast Asia and South America. In combination with MOZAIC and CARIBIC, IAGOS has provided long-term observations of atmospheric chemical composition in the UTLS since 1994. The longest time series are 20 yr of temperature, H2O and O3, and 9–15 yr of aerosols, CO, NO y , CO2, CH4, N2O, SF6, Hg, acetone, ~30 HFCs and ~20 non-methane hydrocarbons. Among the scientific highlights which have emerged from these data sets are observations of extreme concentrations of O3 and CO over the Pacific basin that have never or rarely been recorded over the Atlantic region for the past 12 yr; detailed information on the temporal and regional distributions of O3, CO, H2O, NO y and aerosol particles in the UTLS, including the impacts of cross-tropopause transport, deep convection and lightning on the distribution of these species; characterisation of ice-supersaturated regions in the UTLS; and finally, improved understanding of the spatial distribution of upper tropospheric humidity including the finding that the UTLS is much more humid than previously assumed.

ABSTRACT This study analyses beach morphological change during six consecutive storms acting on the meso‐tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub‐aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run‐up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep‐sloping beaches, since sub‐aerial beach volume reductions up to 30 m 3 /m were followed by intertidal area recovery (–2 < z < 3 m) with rates reaching ~10 m 3 /m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non‐dimensional, morphological parameters. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract Beach nourishments are a widely used method to mitigate erosion along sandy shorelines. In contrast to hard coastal protection structures, nourishments are considered as soft engineering, although little is known about the cumulative, long-term environmental effects of both marine sediment extraction and nourishment activities. Recent endeavours to sustain the marine ecosystem and research results on the environmental impact of sediment extraction and nourishment activities are driving the need for a comprehensive up-to-date review of beach nourishment practice, and to evaluate the physical and ecological sustainability of these activities. While existing reviews of nourishment practice have focused on the general design (motivation, techniques and methods, international overview of sites and volumes) as well as legal and financial aspects, this study reviews and compares not only nourishment practice but also the accompanying assessment and monitoring of environmental impacts in a number of developed countries around the world. For the study, we reviewed 205 openly-accessible coastal management strategies, legal texts, guidelines, EIA documents, websites, project reports, press releases and research publications about beach nourishments in several developed countries around the world (Germany, Denmark, the Netherlands, Belgium, Spain, UK, USA and Australia). Where information was not openly available, the responsible authorities were contacted directly. The study elaborates on the differences in coastal management strategies and legislation as well as the large dissimilarities in the EIA procedure (where applicable) for both marine sediment extraction and nourishment activities. The spatial disturbance of the marine environment that is considered a significant impact, a factor which determines the need for an Environmental Impact Assessment, varies substantially between the countries covered in this study. Combined with the large uncertainties of the long-term ecological and geomorphological impacts, these results underline the need to reconsider the sustainability of nourishments as “soft” coastal protection measures.

BACKGROUND AND PURPOSE: Stenting is increasingly used as an adjunct to medical therapy in symptomatic intracranial stenoses. High periprocedural adverse event rates are one of the limitations of endovascular treatment. Data from the INTRASTENT multicentric registry should demonstrate in-hospital complications at the current stage of clinical development of the stent procedure. METHODS: Participating centers entered the records of all their consecutive intracranial stent procedures into the database. To determine the clinical outcome in the acute phase, we distinguished transient ischemic attack/nondisabling stroke (modified Rankin Scale <2), disabling stroke, death, and intracranial hemorrhage as clinical complications and analyzed whether they were associated with patient- or stenosis-related risk factors. RESULTS: Data from 372 patients with 388 stenoses proved 4.8% disabling strokes and 2.2% deaths. Transient or minor events were detected in 5.4% of the cases. Hemorrhagic events (3.5%) occurred more frequently after treatment of middle cerebral artery stenoses (P=0.004) and were associated with significantly higher morbidity and mortality rates. Ischemic strokes by compromise of perforating branches were detected mainly in the posterior circulation. However, the overall rate of severe adverse events was not dependent from location, degree, and morphology of the stenosis or from patient's age, gender, vascular risk factors, or type of qualifying event. CONCLUSIONS: The complication rates within the registry are within the limits of previously published data. Severe adverse events were equally distributed between potential risk groups with similar rates but different types of main complications in the anterior and posterior circulation.

Abstract. This work investigates historical variation and trends in storm climate for the South Portugal region, using data from wave buoy measurements and from modelling, for the period 1952 to 2009. Several storm parameters (annual number of storms; annual number of days with storms; annual maximum and mean individual storm duration and annual 99.8th percentile of significant wave height) were used to analyse: (1) historical storminess trends; (2) storm parameter variability and relationships; and (3) historical storminess and its relationship to the North Atlantic Oscillation (NAO). No statistically significant linear increase or decrease was found in any of the storm parameters over the period of interest. The main pattern of storm characteristics and extreme wave heights is an oscillatory variability with intensity peaks every 7–8 yr, and the magnitude of recent variations is comparable with that of variations observed in the earlier parts of the record. In addition, the results reveal that the NAO index is able to explain only a small percentage of the variation in storm wave height, suggesting that more local factors may be of importance in controlling storminess in this region.

Abstract A full‐scale controlled experiment was conducted on an excavated and re‐assembled coastal wetland surface, typical of floristically diverse northwest European saltmarsh. The experiment was undertaken with true‐to‐scale water depths and waves in a large wave flume, in order to assess the impact of storm surge conditions on marsh surface soils, initially with three different plant species and then when this marsh canopy had been mowed. The data presented suggests a high bio‐geomorphological resilience of salt marshes to vertical sediment removal, with less than 0.6 cm average vertical lowering in response to a sequence of simulated storm surge conditions. Both organic matter content and plant species exerted an important influence on both the variability and degree of soil surface stability, with surfaces covered by a flattened canopy of the salt marsh grass Puccinellia experiencing a lower and less variable elevation loss than those characterized by Elymus or Atriplex that exhibited considerable physical damage through stem folding and breakage. Copyright © 2015 John Wiley &amp; Sons, Ltd.

The interactions between water, sediment and biology in fluvial systems are complex and driven by multiple forcing mechanisms across a range of spatial and temporal scales. In a changing climate, some meteorological drivers are expected to become more extreme with, for example, more prolonged droughts or more frequent flooding. Such environmental changes will potentially have significant consequences for the human populations and ecosystems that are dependent on riverscapes, but our understanding of fluvial system response to external drivers remains incomplete. As a consequence, many of the predictions of the effects of climate change have a large uncertainty that hampers effective management of fluvial environments. Amongst the array of methodological approaches available to scientists and engineers charged with improving that understanding, is physical modelling. Here, we review the role of physical modelling for understanding both biotic and abiotic processes and their interactions in fluvial systems. The approaches currently employed for scaling and representing fluvial processes in physical models are explored, from 1:1 experiments that reproduce processes at real-time or time scales of 10−1-100 years, to analogue models that compress spatial scales to simulate processes over time scales exceeding 102–103 years. An important gap in existing capabilities identified in this study is the representation of fluvial systems over time scales relevant for managing the immediate impacts of global climatic change; 101 – 102 years, the representation of variable forcing (e.g. storms), and the representation of biological processes. Research to fill this knowledge gap is proposed, including examples of how the time scale of study in directly scaled models could be extended and the time scale of landscape models could be compressed in the future, through the use of lightweight sediments, and innovative approaches for representing vegetation and biostabilisation in fluvial environments at condensed time scales, such as small-scale vegetation, plastic plants and polymers. It is argued that by improving physical modelling capabilities and coupling physical and numerical models, it should be possible to improve understanding of the complex interactions and processes induced by variable forcing within fluvial systems over a broader range of time scales. This will enable policymakers and environmental managers to help reduce and mitigate the risks associated with the impacts of climate change in rivers.

This paper presents the current status of the development of the Lead-cooled Fast Reactor (LFR) in support of Generation IV (GEN IV) Nuclear Energy Systems.The approach being taken by the GIF plan is to address the research priorities of each member state in developing an integrated and coordinated research program to achieve common objectives, while avoiding duplication of effort. The integrated plan being prepared by the LFR Provisional System Steering Committee of the GIF, known as the LFR System research Plan (SRP) recognizes two principal technology tracks for pursuit of LFR technology:- a small, transportable system of 10–100 MWe size that features a very long refueling interval,- a larger-sized system rated at about 600 MWe, intended for central station power generation and waste transmutation.This paper, in particular, describes the ongoing activities to develop the Small Secure Transportable Autonomous Reactor (SSTAR) and the European Lead-cooled SYstem (ELSY), the two research initiatives closely aligned with the overall tracks of the SRP, and outlines the Proliferation-resistant Environment-friendly Accidenttolerant Continual & Economical Reactors (PEACER) conceived with particular focus on burning/transmuting of long-living TRU waste and fission fragments of concern, such as Tc and I.The current reference design for the SSTAR is a 20 MWe natural circulation pool-type reactor concept with a small shippable reactor vessel. Specific features of the lead coolant, the nitride fuel containing transuranics, the fast spectrum core, and the small size combine to promote a unique approach to achieve proliferation resistance, while also enabling fissile self-sufficiency, autonomous load following, simplicity of operation, reliability, transportability, as well as a high degree of passive safety. Conversion of the core thermal power into electricity at a high plant efficiency of 44 % is accomplished utilizing a supercritical carbon dioxide Brayton cycle power converter.The ELSY reference design is a 600 MWe pool-type reactor cooled by pure lead. This concept has been under development since September 2006, and is sponsored by the Sixth Framework Programme of EURATOM. The ELSY project is being performed by a consortium consisting of twenty organizations including seventeen from Europe, two from Korea and one from the USA. ELSY aims to demonstrate the possibility of designing a competitive and safe fast critical reactor using simple engineered technical features while fully complying with the Generation IV goal of minor actinide (MA) burning capability.The use of a compact and simple primary circuit with the additional objective that all internal components be removable, are among the reactor features intended to assure competitive electric energy generation and longterm investment protection. Simplicity is expected to reduce both the capital cost and the construction time; these are also supported by the compactness of the reactor building (reduced footprint and height). The reduced footprint would be possible due to the elimination of the Intermediate Cooling System, the reduced elevation the result of the design approach of reducedheight components.

Physical modelling is a key tool for generating understanding of the complex interactions between aquatic organisms and hydraulics, which is important for management of aquatic environments under environmental change and our ability to exploit ecosystem services. Many aspects of this field remain poorly understood and the use of physical models within eco-hydraulics requires advancement in methodological application and substantive understanding. This paper presents a review of the emergent themes from a workshop tasked with identifying the future infrastructure requirements of the next generation of eco-hydraulics researchers. The identified themes are: abiotic factors, adaptation, complexity and feedback, variation, and scale and scaling. The paper examines these themes and identifies how progress on each of them is key to existing and future efforts to progress our knowledge of eco-hydraulic interactions. Examples are drawn from studies on biofilms, plants, and sessile and mobile fauna in shallow water fluvial and marine environments. Examples of research gaps and directions for educational, infrastructural and technological advance are also presented.

This cross-sectional study was designed to obtain the current prevalence of deep vein thrombosis (DVT) and analyze related risk factors in patients undergoing lumbar interbody fusion. Medical record data were collected from Department of Spinal Surgery, The Third Hospital of Hebei Medical University, between July 2014 and March 2015. Both univariate analysis and binary logistic regression analysis were performed to determine risk factors for DVT. A total of 995 patients were admitted into this study, including 484 men and 511 women, aged from 14 to 89 years old (median 50, IQR 19). The detection rate of lower limb DVT by ultrasonography was 22.4% (223/995) in patients undergoing lumbar interbody fusion. Notably, average VAS (visual analog scale) score in the first 3 days after surgery in the DVT group was more than that in the non-DVT group (Z = -21.69, P < 0.001). The logistic regression model was established as logit P = -13.257 + 0.056*X1 - 0.243*X8 + 2.085*X10 + 0.001*X12, (X1 = age; X8 = HDL; X10 = VAS; X12 = blood transfusion; x = 677.763, P < 0.001). In conclusion, advanced age, high postoperative VAS scores, and blood transfusion were risk factors for postoperative lower limb DVT. As well, the logistic regression model may contribute to an early evaluation postoperatively to ascertain the risk of lower limb DVT in patients undergoing lumbar interbody fusion surgery.

By reducing current velocity, tidal marsh vegetation can diminish storm surges and storm waves. Conversely, currents often exert high mechanical stresses onto the plants and hence affect vegetation structure and plant characteristics. In our study, we aim at analysing this interaction from both angles. On the one hand, we quantify the reduction of current velocity by Bolboschoenus maritimus, and on the other hand, we identify functional traits of B. maritimus' ramets along environmental gradients. Our results show that tidal marsh vegetation is able to buffer a large proportion of the flow velocity at currents under normal conditions. Cross-shore current velocity decreased with distance from the marsh edge and was reduced by more than 50% after 15 m of vegetation. We were furthermore able to show that plants growing at the marsh edge had a significantly larger diameter than plants from inside the vegetation. We found a positive correlation between plant thickness and cross-shore current which could provide an adaptive value in habitats with high mechanical stress. With the adapted morphology of plants growing at the highly exposed marsh edge, the entire vegetation belt is able to better resist the mechanical stress of high current velocities. This self-adaptive effect thus increases the ability of B. maritimus to grow and persist in the pioneer zone and may hence better contribute to ecosystem-based coastal protection by reducing current velocity.

Large-scale experiments were conducted at the Coastal Research Centre (FZK), Germany to characterize the mechanics and characteristics of impact pressures due to breaking waves on a vertical sea wall with a recurve. The characteristics and distribution of impact pressure are found to be greatly depending on the breaking case, so the breaking wave impact is classified into different case like the slow breaking wave, breaking with small air trap and breaking wave with large air trap. When a small air is entrained between the breaking waves and the structure, there is a significant increase in impact pressures. However, if the entrapped air volume increases, impact pressure reduces because of the breaking of waves into smaller water droplets. The impact pressure variation at the vertical wall and recurve along the vertical direction are reported in different breaking cases from the experimental results and the relation between maximum impact pressures with respect to rise time is described by a power equation.

The hydraulic performance and wave loads of single screens and chamber systems were investigated within an extensive test programme at the Large Wave Flume (GWK) in Hannover, which is part of the "Forschungszentrum Küste (FZK)", a joint coastal engineering research centre of both Universities Hannover and Braunschweig. In cases where wave transmission has to be completely avoided (e.g. to achieve sufficient operating time of sea ports) single permeable walls do not provide sufficient protection, hence structures with an impermeable wall have to be considered. A comparison of One- and Multi-Chamber-Systems in terms of the reflection properties and the wave loads demonstrates the advantages of systems with more than one wave chamber. The phase lag analysed between front wall and rear wall of One-Chamber-Systems is particularly investigated and discussed. This paper is mainly dealing with wave forces acting on such structures. Due to strong interrelations between wave forces, wave reflection and surface elevation, the two latter aspects will also be considered.

Large scale experiments have been conducted in the LARGE WAVE CHANNEL of the Forschungszentrum Küste (Coastal Research Centre) in Hannover to investigate the loads acting on a slender circular cylinder attacked by a breaking wave. The wave kinematics, the impact and the cylinder's response were measured simultaneously. For the load measurement two independent methods were used. On the one side pressures were measured and on the other side forces were determined at the bearings. Analysing the data a theoretical description for the two-dimensional impact is confirmed and peak values for the three-dimensional impact are obtained. It is shown that the commonly used calculation method for the impact force fails because the duration of impact is overestimated.

ALARA [Analytic and Laplacian Adaptive Radioactivity Analysis] v1.0,1,2 a new activation code released in January 1998 and developed specifically for the analysis of radioactivity in fusion energy systems, has been validated by comparison to other commonly used activation codes, FISPACT-973 and DKR-Pulsar 2.04 using the International Atomic Energy Agency [IAEA] Fusion Evaluated Nuclear Data Library [FENDL] Calculational Activation Benchmark.5 The solutions to the benchmark problem for both steady-state and pulsed operation have been calculated with all three programs on the same IBM RS/6000 workstation. In addition to comparing the total activity in each of the 44 non-void zones and the isotopic contributions to the activity at specific spatial points, the required computing time has been compared. For the steady state problem, agreement between ALARA and FISPACT-97 for the total activity was within 2.5% in all zones at all cooling times, and within 0.5% in most zones. For both the steady state and pulsed problem, agreement between ALARA and DKR-Pulsar 2.0 was within 1% in all zones and at all cooling times where tritium inventories were not significant. The agreement between ALARA and FISPACT-97 for the individual isotopic inventories in the stainless steel first wall back-plate were within 1% for all dominant isotopes at all cooling times, while the DKR-Pulsar 2.0 results showed some significant discrepancies. The processing time for ALARA is 2/3 of that for DKR-Pulsar 2.0 and less than 1/5 of that for FISPACT-97. This validation exercise proves that ALARA is an accurate and fast computational tool for the calculation of induced activity in fusion power systems.

The interaction of hafnium(IV) and thorium(iv) with humic acid, HA, is studied using EXAFS and compared to the interaction of these metal ions with carboxylate groups of the cation exchanger Bio-Rex70. Fourier-f'fltered Hf and Th I-,3 edge transmission EXAFS for the first oxygen shell is analyzed. For both Hf(IV)-HA and Hf(IV)-Bio-Rex70, in wet paste and air-dried forms, 6-7 oxygen atoms at R=2.14 A are found. Th(IV)-HA also exhibits coordination similar to Th(IV)-Bio-Rex70. These observations support conclusions from previous studies on U(VI)-HA that metal cations are sorbed primarily onto HA carboxylate groups; other HA functional groups play a less significant role.

Quarante-neuf organismes européens rassemblent dans le réseau <b>SARNET<b/> (Severe Accident Research and management NETwork) leurs moyens de recherche sur les accidents graves de réacteur, afin de réduire les problèmes importants en suspens dans ce domaine, et ainsi contribuer à l'amélioration de la sûreté des centrales nucléaires actuelles et futures. Le projet a été défini en prenant en compte la nécessité d'optimiser l'utilisation des moyens disponibles en Europe, et d'associer de manière pérenne les complémentarités des laboratoires de recherche. SARNET s'attaque à la fragmentation existant entre les différents programmes nationaux de R&D, notamment en élaborant en commun des programmes de recherche ainsi que des outils de calcul et des méthodologies pour les évaluations de sûreté. Coordonné par l'IRSN le réseau SARNET rassemble la plupart des acteurs impliqués dans la recherche sur les accidents graves en Europe.Pour atteindre ces objectifs, toutes les membres du réseau SARNET contribuent à un programme d'activités commun (JPA), constitué de plusieurs éléments :• Mise en oeuvre d'un outil de communication avancée pour favoriser l'échange d'informations ;• Harmonisation et réorientation de programmes de recherche et définition commune de nouveaux programmes ;• Analyse des résultats expérimentaux fournis par les programmes de recherche afin d'aboutir à une compréhension commune des phénomènes concernés ;• Développement du logiciel ASTEC (outil de calcul permettant de simuler le comportement d'un réacteur nucléaire lors d'un accident grave) qui capitalise en termes de modèles physiques les connaissances élaborées par SARNET ;• Développement de bases de données scientifiques dans lesquelles tous les résultats des programmes de recherche sont stockés ;• Développement d'une méthodologie commune pour les évaluations probabilistes de sûreté des réacteurs ;• Enseignement, formation et rédaction d'ouvrages ;• Mise en oeuvre d'un programme de mobilité de personnels entre les divers organismes membres du réseau.Le réseau a atteint en terme de compétence, dans le domaine des accidents graves et pour l'ensemble des réacteurs nucléaires en Europe, la masse critique nécessaire à la réalisation et l'interprétation de programmes expérimentaux ainsi qu'au développement de modèles et à leur intégration dans le logiciel ASTEC. Quelques organismes couvrent un large éventail de compétences, qui sont compétées par l'apport de contributions spécialisées dans des domaines très spécifiques.Afin de préserver les intérêts des différents membres du réseau, une politique claire en termes de protection de la propriété intellectuelle a été définie. Les documents contenant des données "protégées" ne sont remis qu'aux membres qui, de par l'activité qu'ils proposent, augmentent de manière importante la valeur des données (production d'analyses, développement de modèles et évaluation). Néanmoins, les méthodologies d'évaluation de sûreté et le logiciel ASTEC, produits intégrateurs des connaissances et modèles élaborés au sein de SARNET, seront disponibles pour tous les membres du réseau et les autres organismes européens désireux de les utiliser pour des évaluations de sûreté ou pour l'amélioration de leurs centrales nucléaires.

Abstract: Biofilms constitute an important issue in microbial ecology, due to their high ecological and economic relevance, but the impact of abiotic conditions and microbial key players on the development and functionality of a natural biofilm is still little understood. This study investigated the effects of light intensity (LI) and bed shear stress (BSS) and the role of dominant microbes during the formation of natural biofilms and particularly the process microbial biostabilization. A comprehensive analysis of microbial biomass, extracellular polymeric substances produced, and the identification of dominant bacterial and algal species was correlated with assessment of biofilm adhesiveness/stability. LI and BSS impacted the biofilms in very different ways: biofilm adhesiveness significantly increased with LI and decreased with BSS. Moreover, microbial biomass and the functional organization of the bacterial community increased with LI, while the dynamics in the bacterial community increased with BSS. Most stable biofilms were dominated by sessile diatoms like Achnanthidium minutissimum or Fragilaria pararumpens and bacteria with either filamentous morphology, such as Pseudanabaena biceps , or a potential high capacity for extracellular polymeric-substance production, such as Rubrivivax gelatinosus . In contrast, microbes with high motility, such as Nitzschia fonticola , Pseudomonas fluorescens , and Caulobacter vibrioides , dominated the least adhesive biofilms. Their movement and potential antibiotic production could have had a disruptive impact on the biofilm matrix, which decreased its stability. This is the first study to unveil the link between abiotic conditions and resulting shifts in key microbial players to impact the ecosystem-service microbial biostabilization. Keywords: microbial biostabilization, natural biofilms, abiotic factors, microbial community, mesocosm

Worldwide, seagrass meadows are under threat. Consequently, there is a strong need for seagrass restoration to guarantee the provision of related ecosystem services such as nutrient cycling, carbon sequestration and habitat provision. Seagrass often grows in vast meadows in which the presence of seagrass itself leads to a reduction of hydrodynamic energy. By modifying the environment, seagrass thus serves as foundation species and ecosystem engineer improving habitat quality for itself and other species as well as positively affecting its own fitness. On the downside, this positive feedback mechanism can render natural recovery of vanished and destroyed seagrass meadows impossible. An innovative approach to promote positive feedback mechanisms in seagrass restoration is to create an artificial seagrass (ASG) that mimics the facilitation function of natural seagrass. ASG could provide a window of opportunity with respect to suitable hydrodynamic and light conditions as well as sediment stabilization to allow natural seagrass to re-establish. Here, we give an overview of challenges and open questions for the application of ASG to promote seagrass restoration based on experimental studies and restoration trials and we propose a general approach for the design of an ASG produced from biodegradable materials. Considering positive feedback mechanisms is crucial to support restoration attempts. ASG provides promising benefits when habitat conditions are too harsh for seagrass meadows to re-establish themselves.

Abstract Although tidal marshes are known for their coastal defense function during storm surges, the impact of extreme wave forcing on tidal marsh development is poorly understood. Seedling survival in the first season after germination, which may involve exposure to extreme wave events, is crucial for the natural establishment and human restoration of marshes. We hypothesize that species‐specific plant traits plays a significant role in seedlings survival and response to wave induced stress, i.e., through stem bending and uprooting. To test this hypothesis, seedlings of pioneer species ( Bolboschoenus maritimus , Schoenoplectus tabernaemontani , Spartina anglica , and Puccinellia maritima ) with contrasting biophysical traits were placed in the Large Wave Flume in Hannover (Germany) and exposed to storm wave conditions. Seedlings of P. maritima and S. anglica experienced a lower loss rate and bending angle after wave exposure compared to S. tabernaemontani and especially B. maritimus . The higher loss rates of B. maritimus and S. tabernaemontani result from deeper scouring around the stem base. Scouring depth was larger around stems of greater diameter and higher resistance to bending. Here, B. maritimus and S. tabernaemontani have both thicker and stiffer stems than S. anglica and P. maritima . Our results show that especially seedlings with thicker stems suffer from erosion and scouring, and have the highest risk of being lost during extreme wave events. This implies that for successful seedling establishment and eventually the establishment of a mature tidal marsh vegetation, the species composition and their capacity to cope with storm wave disturbances is crucial.