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Contains fulltext : 35149.pdf (Publisher’s version ) (Open Access) 148 p.

A three-dimensional hydrodynamic and sediment transport model was used to study the relative impact of (1) vegetation, (2) micro-topography, and (3) water level fluctuations on the spatial flow and sedimentation patterns in a tidal marsh landscape during single inundation events. The model incorporates three-dimensional (3-D) effects of vegetation on the flow (drag and turbulence). After extensive calibration and validation against field data, the model showed that the 3-D vegetation structure is determinant for the flow and sedimentation patterns. As long as the water level is below the top of the vegetation, differences in flow resistance between vegetated and unvegetated areas result in faster flow routing over unvegetated areas, so that vegetated areas are flooded from unvegetated areas, with flow directions more or less perpendicular to the vegetation edge. At the vegetation edge, flow velocities are reduced and sediments are rapidly trapped. In contrast, in between vegetated areas, flow velocities are enhanced, resulting in reduced sedimentation or erosion. As the water level overtops the vegetation, the flow paths described above change to more large-scale sheet flow crossing both vegetated and unvegetated areas. As a result, sedimentation patterns are then spatially more homogeneous. Our results suggest that the presence of a vegetation cover is the key factor controlling the long-term geomorphic development of tidal marsh landforms, leading to the formation of (1) unvegetated tidal channels and (2) vegetated platforms with a levee-basin topography in between these channels. [KEYWORDS: hydrodynamic modeling ; sediment transport ; wetlands ; floodplain dynamics ; riparian systems]

Contrasting soil conditions caused by different inundation frequencies require different root growth strategies along the elevational gradient of coastal salt marshes. The objective of this study was to examine (1) if root lifespan was shorter in Elymus pycnanthus, a relatively fast-growing competitive species dominating high marshes, than in Spartina anglica, a relatively slow-growing stress-tolerating species dominating low marshes, and (2) if the species with longer lifespan had higher tissue density (g cm-3) and lower specific root length (m g-1) than the species with shorter lifespan. Root production and mortality rates were established by sampling roots in in-growth cores, and using triphenyltetrazolium chloride (TTC) staining to distinguish vital from dead roots. Root lifespan was estimated by dividing the living root biomass (Elymus: 36 g m-2, Spartina: 100 g m-2) by root production (Elymus: 0.28 g day-1 m-2, Spartina: 0.25 g day-1 m-2) or root mortality rates (Elymus: 0.42–0.53 g day-1 m-2). Spartina did not exhibit substantial mortality. Despite the present method only yielding rough estimates of average root lifespan, it is evident that root longevity is much shorter in Elymus than in Spartina. Root lifespan ranged between 10–19 weeks for Elymus but was close to 1 year in Spartina, indicating that Elymus replaces it's roots continuously throughout the growing season, whereas Spartina maintains its roots over the growing season. Fine roots of Elymus had slightly lower tissue density (0.094) than those of Spartina (0.139), whereas coarse roots of Elymus and Spartina had similar tissue density (0.100 g cm-3). Fine roots of Elymus and Spartina had similar specific root length (195 m g-1). However, coarse roots of Elymus (50 m g-1) had higher specific root length than those of Spartina (20 m g-1) due to having smaller root diameter (Elymus: 548 µm, Spartina: 961 µm). We conclude that present observations on Elymus and Spartina support our first hypothesis that the ‘competitive’ species from the high marsh had short-lived roots compared to the ‘stress-tolerating’ species from the low marsh. However, our result provide only weak support for the existence of a positive correlation between root longevity and tissue density and a negative correlation between root longevity and specific root length. [KEYWORDS: Root diameter, Root lifespan, Root turnover, Specific root length, Tidal marsh, Tissue density]

The salt marshes along the Western Scheldt Estuary have very distinct spatial vegetation patterns, depending on salinity (between marshes), elevational gradients (within marshes) and hydrodynamics (within marshes). We will start with a brief description of the plant species distribution both within and between marshes, briefly explain some of the most important underlying physiological plant characteristics, and briefly elucidate some of the consequences for biochemical processes (research focus of former NIOO-department of Littoral Vegetations). We will then introduce our current research on plant-benthos interactions and on hydrodynamic processes in salt marshes (research focus of the in January 2002 founded NIOO-department Spatial Ecology). This summer, we did an extensive sampling campaign to identify the macro-benthos within vegetations at different elevational heights (i.e., macro algae vs. Zostera noltii meadows vs. Spartina marsh). We also manipulated the environment for the benthos in parts of the Spartina marsh. With respect to hydrodynamics, we measured wave energy, current velocities and sediment load in the water column, during the plant growth season 2002. In addition, we performed detailed experiments in a laminar-flow flume and in a wave-generating flume, using both natural and artificial vegetations. Preliminary results will be discussed.

In citrus, the majority of fine roots are distributed near the soil surface - a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant's below-ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q(10) = 1.8-2.0), provided that the changes in temperature were short-term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 degreesC, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO2 concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO2 concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material. Root respiration was strongly affected by diurnal fluctuations in temperature (Q(10) = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO2 concentrations (400 to 25000 ppm CO2; pH around 6). Soil CO2 was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter me [KEYWORDS: Citrus volkameriana Tan. & Pasq.; CO2-diffusion gradient; root respiration; soil CO2 concentration; Volkamer lemon]

Quantitative knowledge of both photosynthesis and respiration is required to understand plant growth and resulting crop yield. However, especially the nature of the energy demanding processes that are dependent on dark respiration in full-grown tissues is largely unknown. The main objective of the present study was to establish the identity and energy requirements of the most important of these (maintenance) processes, and to gain insight in methods of determining the rates and specific costs of these processes. Developing such methods is more important than obtaining data on the rates of maintenance processes for certain crops, as these rates are likely to vary as a function of e.g. the environmental conditions, developmental stage and species.Leaf respiration rates of 15 potato cultivars (Solanum tuberosum L.) differed significantly (chapter 2). To examine whether growth and maintenance requirements differed, two cultivars were compared. After synchronizing their development, leaf protein content, shoot and leaf respiration, photosynthetic light response curves and the growth parameters (i.e. RGR, LAR, SLA, and LWR) were similar, thus excluding potential differences in growth and maintenance respiration. It was concluded that it is important to study the physiological cause of respiratory differences, before starting to select genotypes for low respiration rate.Protein turnover is generally regarded as an important maintenance process. The component of dark respiration rate associated with overall protein turnover of tissues was quantified in vivo by the use of an inhibitor of cytosolic protein synthesis (chapter 3). The in vivo effect of this inhibitor was assessed by monitoring the inhibition of the induction of the ethyleneforming enzyme activity. The respiratory costs of protein turnover were maximally 17 - 35% of total respiration. The maximum degradation constants (i.e. K d -values) derived for growing and full-grown leaves were up to 2.42 x 10 -6and 1. 12 x 10 -6s -1, respectively.Nocturnal carbohydrate export is another process requiring respiratory energy. The potential contribution of the energy requirements associated with nocturnal carbohydrate export to i) the fraction of dark respiration affected by leaf nitrogen concentration and ii) the dark respiration of mature source leaves, was explored (chapter 4). The estimate of the specific energy cost involved in carbohydrate export (0.70 mol C0 2 [mol sucrose]-1), agrees well with both literature data (0.47 to 1.26) and the theoretically calculated range for starch-storing species (0.40 to 1.20). Maximally 42 to '107'% of the effect of the leaf organic nitrogen concentration on the dark respiration of primary bean leaves, is ascribed to the energy costs associated with nocturnal export of carbohydrates. Total energy costs associated with export account on average for 29% of the dark respiration rate for various starch-storing species.The respiratory energy requirements of maintaining ion gradients were quantified on plant roots (chapter 5). Combining the anion efflux rate (35 neq [g dry weight] -1s -1) with literature data on the specific costs of ion transport, suggests that energy costs associated with re-uptake of ions may account for up to 66% of the total respiratory costs involved in (an)ion influx. A value of 34% of the total respiratory costs involved in (an)ion influx was obtained if the net uptake rate was based on the relative growth rate observed for potato, and assuming phosphate and sulfate to be both 10% of nitrate in- and efflux. Comparison of relative values of the respiration of root and shoot is not useful, as in both tissues other processes add to the total.Estimating the respiratory energy requirements of maintaining ion gradients is complicated by lack of knowledge on efflux kinetics. Therefore, efflux kinetics was studied, using a dynamic simulation model (chapter 6). Simulations showed that the overall efflux kinetics observed in the medium may differ significantly, even if actual efflux rates (and thus costs involved in maintaining ion gradients) in the simulations were equal. Similarly, the relative contribution of ions originally located in the apoplast, cytoplasm and vacuole of different cell layers to these efflux kinetics and the observed cumulative efflux originating from the symplast were different. All these differences were due to the presence or absence of an endodermis, different pathways involved in net uptake and different number of cell layers involved in efflux.Integration of the available knowledge on maintenance, growth and uptake processes enabled to explain the respiration of potato roots. The costs calculated for protein turnover could explain total maintenance requirements (10.2 to 14.8 nmol O 2 [g DW] -1s -1). It was deduced that overall costs for maintaining solute gradients (i.e. re-uptake balancing efflux) account for up to 33% of the overall costs of nitrate influx (i.e. 1/U is up to a factor 1.5 higher if efflux takes place). This agrees well with the results of chapter 5.

Hydrodynamic impacts of vegetation in the intertidal zone are highly important to coastal protection. However, most studies on hydrodynamic impacts of vegetation in the intertidal zone are carried out in flumes. This results in a lack of field data for validating models that describe short-term hydrodynamic impacts of vegetation. The current research focuses on field measurements of flow patterns and waves in vegetated intertidal areas. Ample measurement devices are available to measure hydrodynamic processes in the field. Examples are: acoustic Doppler current profilers (ADCP), high resolution acoustic Doppler current profilers (HR-ADCP) and acoustic Doppler velocity meters (ADV). This study focuses on the differences in the performance of these devices, to determine which of them can be best deployed in a future fieldwork campaign in mangroves. Major points of attention in this comparison are the accuracy of the data and the potential disturbance of the measurements by the presence of vegetation. It is concluded that ADV’s perform very well in vegetated intertidal areas, while (HR-)ADCP’s show difficulties when deployed upward looking. Furthermore, ADV’s are preferred over (HR-)ADCP’s due to their ability of combining high frequent wave and current measurements and their convenient deployment.

This paper reports on the preliminary results from a true-to-scale flume experiment carried out to better understand plant and sediment responses, as well as their interactions, under extreme hydrodynamic forcing in shallow coastal salt and brackish water marsh settings. We report here on bed level changes under individual plant seedlings and denser plant arrangements transplanted from seed and field sites on the Scheldt estuary and on the response of vertically extracted sediment cores from two UK field sites with contrasting sediment characteristics and plant species occupying the surface. Due to the relatively recent completion of the experiment in addition to time-consuming, complex data processing and analysis methods more time is required before definitive quantitative results can be reported. Initial insights into the general behaviour of salt marsh sediments under horizontal and vertical wave-driven hydrodynamic forcing, however, confirm marsh surfaces to be highly stable structures, at least during extreme storm surge events.

Tidal marshes often present cyclic dynamics, with alternating phases of expansion and lateral retreat. Marsh seedling establishment is a primary condition for marsh colonization and expansion. Successful establishment is often episodic due to bio-physical thresholds, as expressed in the ‘Windows of Opportunity’ concept. Identifying critical factors and understanding how they enable or hamper seedling establishment, is highly relevant for coastal management and restoration schemes. This study quantified the effects of critical factors in tidal marsh establishment processes. Firstly, by exposing marsh seedlings to different disturbances in terms of sedimentation regime and wave exposure, this study found that these disturbances affect seedling establishment both directly and via bio-morphological adjustments (Chapter 2 and 3). Secondly, channel related drainage relief was found to facilitate seedling survival, especially in the early phase of marsh establishment in muddy systems (Chapter 4). Thirdly, by using marsh seedlings with different disturbance-free periods in both laboratory and field experiments, this study confirmed that a longer disturbance-free period can strongly enhance seedling survival as well as their resistance to later extreme disturbances (Chapter 2 and 4). The erosion of tidal marshes often leads to the development of a cliff at the boundary between tidal flat and marsh. The formation of a cliff shifts marsh development from a phase of lateral expansion to a retreating phase, as a result of the interdependent feedbacks between marsh vegetation and external forcing. This thesis investigated the tipping point conditions of cliff formation at marsh edges with different marsh species. The clonal growth of vegetation at marsh edges was found to respond to different sediment types and to affect the cliff formation processes. Species-specific clonal growth strategies in step length have important effects on initiating cliffs, lateral retreat and thus landscape dynamics at marsh edges (Chapter 5). In summary, this study provides mechanistic insight into the primary expansion (i.e., seedling establishment) of tidal marshes under a variety of critical forcing factors, as well as insight in the factors contributing to cliff formation and the onset of lateral retreat. It highlights the variability in relevant species-specific responses, as well as the importance of location-dependent factors. These results add quantitative support to models predicting the critical transitions in marsh dynamics, both marsh expansion and marsh retreat. The findings of this study are instructive for marsh restoration and nature based coastal defense schemes. While they contribute to understanding the overall stability of marsh ecosystems in the face of global change, they also highlight the need for tailor-made solutions for the application of nature-based solutions at particular locations.

Contains fulltext : 225923.pdf (Publisher’s version ) (Open Access) Radboud University, 19 november 2020 Promotores : Lamers, L.P.M., Heide, Tijsse van der, Bouma, T.J. Co-promotor : Lengkeek, W. 203 p.

Contains fulltext : 201202.pdf (Publisher’s version ) (Open Access) Radboud University, 01 maart 2019 Promotores : Herman, P.M.J., Hendriks, A.J., Bouma, T.J Co-promotor : Katwijk, M.M. van 192 p.

Foreshore Assessment using Space Technology (FAST, 2014 - 2018) is a project funded by the European Union's (EU) Seventh Framework Programme (FP7) for research, technological development and demonstration under grant agreement number 607131. FAST is developing down-stream services for the European Earth Observation Programme Copernicus to support cost-effective, nature-based shoreline protection against flooding and erosion. This book aims to communicate the services generated by the FAST project to the general public as well as provide its readers with information on how to access its products after the project lifetime.

Despite being highly valuable ecosystems, seagrass meadows are threatened worldwide, mostly by human activities. In order to preserve seagrass meadows from collapse, we need to better understand their resilience in a changing environment. By means of various manipulative field experiment in temperate systems, the present thesis addressed seagrass resilience by looking at (i) indicators of resilience as needed for monitoring; (ii) strategies and mechanisms of resilience allowing seagrasses to resist stresses and to recover from disturbances; and (iii) the influence of climatic –latitudinal –gradients as drivers of seagrass traits, resilience and indicators.Indicators of resilienceIndicators are needed in order to monitor seagrass ecosystems and to predict nearness to collapse. In this thesis, we raised the question on the proper interpretation of indicators to estimate seagrass health and resilience. We compared the response of two indicators: i) vegetation cover, which is a traditionally used indicator to asses the seagrass health status; and ii)critical slowing downwhich is a theoretically suggested indicator for seagrass health status in terms of resilience to disturbances, expressed asrelative recovery from disturbance. The two indicators showed an opposite response to disturbance: the higher the cover, the lower the relative recovery from disturbance (Chapter 2). This was however only observed during the seagrass growing phase (Chapter 3). Indeed, we noticed that the timing of a disturbance relative to the seagrass seasonal growth period, were crucial for seagrass resilience, with highest recovery at the start of the growing season, and a decreasing recovery with higher cover (Chapter 3). This conflicting response between indicators was observed independently from wave exposure or nutrient status (i.e. same response even under eutrophication stress). These results do emphasis the need to carefully consider timing of monitoring of the indicators, as it forms a fundamental factor to evaluate indicators in terms of resilience. These findings are likely to extent beyond seagrass, also to other temperate seasonal ecosystems.CHAPTER 9176Strategies/mechanisms for resilienceSeagrasses have the capacity to adapt to their environment by changing their morphological, physiological and mechanical traits. They moreover present different strategies, related to their growth rate (Grime, 1977), resource allocation or ecosystem engineering that make them more or less resilient to stresses and disturbances and preserve them from collapse.In this thesis, we observed that the plant’s responses to stress and disturbances deviated from the response predicted by Grime’s growth strategies, under the influence of ecosystem engineering (Chapter 4). That is, the fast-growing seagrass species was not only a better recoloniser after disturbance as compared to a slower-growing species, but also more resistant to sulphide invasion. This higher resistance was explained by its strong capacity to reduce the stress through ecosystem engineering (i.e. release of oxygen through their root system). Ecosystem engineering hence forms an essential strategy to cope with stressful and disturbed environment by making some seagrass species more resilient. We speculate that this effect depends however on the nature of the ecosystem engineering (i.e. based on physiological or structural traits) as well as the nature of the environment (i.e. stimulating growth or stimulating the formationof physically strong tissues).Another strategy for resilience evidenced in this thesis was related to their resource allocation and more specifically the use of their carbon reserves for resilience. Being photosynthetic organisms, seagrasses can store carbon reserves in their rhizomes during their seasonal growth. These reserves are stored in the form of non-structural carbohydrates and mostly used for growth or to survive the winter period. We showed that, when experiencing short-term stress events, seagrasses use their carbohydrate reserves to recover and regrow, particularly the fast-growing species (Chapter 4 and 5). Overall, we saw that the use of carbohydrate reserves as a resilience mechanism increased depending on the species (i.e. fast growth strategy), the environmental conditions (i.e. exposure to hydrodynamics, nutrient status), the climatic settings (cold winter temperatures and low daily light doses) and the occurrence of short-term stress events during their seasonal growth. It can be speculated thaton the short-term, the use of carbon reserves for regrowth is beneficial for the plants. But on the long-term, the over-consumption of their reserves to recover from disturbance SUMMARY177might be enough to tip the system and lead to collapse, particularly when done at the end of the season (Chapter 5).Being sessile organisms, seagrasses have the capacity to modify their structure or traits to resist the adverse effect of biotic or abiotic stressors such as waves or currents. It is known that the mechanical resistance of seagrass leaves to physical stress depends on their species-specific traits (i.e. growth strategies). In this thesis we also showed that seagrasses could adapt their mechanical traits depending on their distribution along a seasonal or latitudinal gradient but also depending on their environment such as their nutrient status (Chapter 6). In eutrophic conditions, seagrasses presented more brittle leaves, easier to break but also more extensible than in more oligotrophic conditions. This plasticity and adaptation to their local environmental conditions forms hence another important strategy for resilience.The influence of climatic –latitudinal-gradientsSeagrasses can be found in temperate systems along a large gradient of environmental and climatic conditions, controlling the length of their seasonal growth and their population dynamics. With this thesis we demonstrated that these gradients could play an important driving role on their traits such as their reproductive success, carbon reserves, physiological and mechanical traits (Chapters 5 to 7). We also observed that the seasonal dimension of seagrass growth in temperate systems plays a major driving role for seagrass resilience, particularly the winter period (Chapter 5) and the peak of growth (Chapter 3). In fact, depending on their local conditions and distribution along a climatic –latitudinal –gradient, seagrasses present different traits, shaping their resilience to external stresses or disturbances. The northern-European populations may be considered to be in a perpetually colonizing phase with yearly recurrent population initiation by sexual propagules (seeds) (Chapter 7), making them genetically more diverse; and by asexual –clonal –extension of the dormant rhizomes relying on their carbon reserves (Chapter 5). In contrast, the southern, evergreen populations depend much more on clonal propagation, hence being productive all year due to suitable light and temperature conditions for photosynthesis; and relying less on their carbon reserves (Chapter 5) or seed production (Chapter 7), with mechanically stronger leaves (Chapter 6). CHAPTER 9178Conclusions and implicationsOverall, all the mechanisms involved in seagrass resilience as well as the influence of global trends have considerable consequences on the seagrass resilience and the stability of coastal ecosystems in the long-tem. Seagrasses can adapt to their changing environment, as observed along a climatic –latitudinal –gradient. But additional effects of short-term stresses such as e.g. nutrient enrichment inducing eutrophication, might push the system towards its bifurcation point. In that situation, even a small disturbance may induce a meadow to collapse, due to a reduced resistance to stress and recovery potential. The consequences of such collapse are large for the overall health of the coastal ecosystems. In general, a lowered resilience of seagrass meadows can affect their efficiency as ecosystem engineers and thus the positive feedbacks they induce. The maintenance of positive feedbacks for seagrass meadows is essential, as this affects their strategies for resilience (for instance, capacity to reduce sulphide stress through their root system) and their capacity to adapt to climatic gradients.Our findings bear implications for the management of seagrass meadows. In a context of climate change and increasing occurrence of stochastic events (i.e. storms, extreme weather) and human-induced stresses, managers, scientists and stakeholders should consider the importance of: when (seasonal growth), where (latitudinal –climatic gradient) and how (nature of the threat, resilience strategies) seagrass resilience might be affected. Considering these parameters is essential to better preserve temperate seagrass meadows from collapse and to maintainthe stability of their ecosystems

Contains fulltext : 155841.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 08 maart 2016 Promotor : Herman, P.M.J. Co-promotor : Bouma, T.J. 142 p.

Tidal flat landscape formation and evolution are closely related to the biotic and abiotic processes that take place in the intertidal environments. Extensive studies have been carried out on the relevant agents such as hydrodynamics, sediment transport and the related ecosystem (vegetation and benthic communities) dynamics. However, the feedback mechanism among multiple agents is complex and many key aspects are currently understudied. In times of accelerating global change, knowledge of the mechanisms that drive tidal flat evolution is of great importance to ecosystem conservation and restoration. This thesis addresses the currently understudied subjects related to intertidal hydrodynamic processes as well as the intertidal landscape developments, which are of great economic and ecological importance.

Coastal defence structures are proliferating as a result of rising sea levels and stormier seas. With the realisation that most coastal infrastructure cannot be lost or removed, research is required into ways that coastal defence structures can be built to meet engineering requirements, whilst also providing relevant ecosystem services—so-called ecological engineering. This approach requires an understanding of the types of assemblages and their functional roles that are desirable and feasible in these novel ecosystems. We review the major impacts coastal defence structures have on surrounding environments and recent experiments informing building coastal defences in a more ecologically sustainable manner. We summarise research carried out during the THESEUS project (2009–2014) which optimised the design of coastal defence structures with the aim to conserve or restore native species diversity. Native biodiversity could be manipulated on defence structures through various interventions: we created artificial rock pools, pits and crevices on breakwaters; we deployed a precast habitat enhancement unit in a coastal defence scheme; we tested the use of a mixture of stone sizes in gabion baskets; and we gardened native habitat-forming species, such as threatened canopy-forming algae on coastal defence structures. Finally, we outline guidelines and recommendations to provide multiple ecosystem services while maintaining engineering efficacy. This work demonstrated that simple enhancement methods can be cost-effective measures to manage local biodiversity. Care is required, however, in the wholesale implementation of these recommendations without full consideration of the desired effects and overall management goals.

Contains fulltext : 135165.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 12 december 2014 Promotor : Herman, P.M.J. Co-promotores : Bouma, T.J., Katwijk, M.M. van 237 p.

Contains fulltext : 131904.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 04 september 2014 Promotores : Herman, P.M.J., Ziegler, A.D. Co-promotor : Bouma, T.J. 169 p.

Contains fulltext : 101061.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 22 maart 2013 Promotores : Herman, P.M.J., Roelofs, J.G.M. Co-promotor : Bouma, T.J. 138 p.