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In dit onderzoek staat centraal de vraag of Maria de Medici in staat is om in de periode van haar ballingschap van 1631-1642 in staat is om te werken aan haar zelfrepresentatie en haar macht te doen gelden door middel van de kunsten.

De devotie van de middeleeuwer geeft een inzicht in het gebruik van de zijkapellen in de Nederlandse middeleeuwse kerken. De overeenkomst en de verschillen in gebruik en architectuur tussen de zijkapellen in vier Nederlandse middeleeuwse kerken wordt besproken.

There is a growing recognition of the important role of scale-dependent feedback for biogeomorphological landscape formation, where organisms locally improve survival and growth but at the same time negatively affect organisms at larger distance. However, little is known on how scale-dependent bio-geomorphic feedback is influenced by organism traits in combination with abiotic forcing. This was studied by measuring in a flume, the flow patterns around patches of three contrasting marsh species (Spartina anglica, Puccinellia maritima and Salicornia procumbens), using the flow acceleration around vegetation patches and deceleration within vegetation patches as quantitative proxy for the negative and positive feedback to the vegetation performance. The importance of external forcing was assessed by comparing three realistic current velocities: 0.1, 02 and 0.3 m s(-1). Our results showed that the dense clonal growth of stiff Spartina anglica shoots caused strongest flow deviations, irrespective of the applied current velocity. In contrast, the more sparsely growing, shorter stiff shoots of Salicornia procumbens induced much less flow deviation, allowing more water to pass through and over the vegetation canopy. The dense but highly flexible shoots of Puccinellia maritima caused strong flow deviations at low velocities, which diminished at higher velocities due to bending of the vegetation. Overall, these hydrodynamic results demonstrate that plant species traits interact with environmental conditions in creating scale-dependent feedbacks explaining why the effects of vegetation on landscape formation in saltmarshes are species specific.

[1] Feedback between vegetation growth, water flow, and landform is important for the biogeomorphic evolution of many landscapes, such as tidal marshes, alluvial rivers, and hillslopes. While experimental studies often focus on flow reduction within static homogeneous vegetation, we concentrate on flow acceleration around and between dynamically growing vegetation patches that colonize an initially bare landscape, with specific application to Spartina anglica, a pioneer of intertidal flats. Spartina patches were placed in a large-scale flow facility of 16 × 26 m, simulating the growth of two vegetation patches by increasing the patch diameter (D = 1–3 m) and decreasing the interpatch distance (d = 2.3–0 m). We quantified that the amount of flow acceleration next to vegetation patches, and the distance from the patch where maximum flow acceleration occurs, increases with increasing patch size. In between the patches, the accelerated flow pattern started to interact as soon as D/d ≥ 0.43–0.67. As the patches grew further, the flow acceleration increased until D/d ≥ 6.67–10, from which the flow acceleration between the patches was suppressed, and the two patches started to act as one. These findings are in accordance with theory on flow around and between nonpermeable structures; however, the threshold D/d values found here for permeable vegetation patches are higher than those for nonpermeable structures. The reported flow interactions with dynamic vegetation patches will be essential to further understanding of the larger-scale biogeomorphic evolution of landscapes formed by flowing water, such as tidal flats, floodplain rivers, and hillslopes., [1] Feedback between vegetation growth, water flow, and landform is important for the biogeomorphic evolution of many landscapes, such as tidal marshes, alluvial rivers, and hillslopes. While experimental studies often focus on flow reduction within static homogeneous vegetation, we concentrate on flow acceleration around and between dynamically growing vegetation patches that colonize an initially bare landscape, with specific application to Spartina anglica, a pioneer of intertidal flats. Spartina patches were placed in a large-scale flow facility of 16 × 26 m, simulating the growth of two vegetation patches by increasing the patch diameter (D = 1–3 m) and decreasing the interpatch distance (d = 2.3–0 m). We quantified that the amount of flow acceleration next to vegetation patches, and the distance from the patch where maximum flow acceleration occurs, increases with increasing patch size. In between the patches, the accelerated flow pattern started to interact as soon as D/d ≥ 0.43–0.67. As the patches grew further, the flow acceleration increased until D/d ≥ 6.67–10, from which the flow acceleration between the patches was suppressed, and the two patches started to act as one. These findings are in accordance with theory on flow around and between nonpermeable structures; however, the threshold D/d values found here for permeable vegetation patches are higher than those for nonpermeable structures. The reported flow interactions with dynamic vegetation patches will be essential to further understanding of the larger-scale biogeomorphic evolution of landscapes formed by flowing water, such as tidal flats, floodplain rivers, and hillslopes.

To unravel the relation between hydrodynamic forcing and the dynamics of the tidal flat–salt-marsh ecosystem, we compared hydrodynamic forcing in terms of proxies relevant to bed sediment motion for four tidal flat–salt-marsh ecosystems that were contrasting in terms of wind exposure (sheltered vs. exposed) and lateral development (shrinking vs. expanding). Wave and current field measurements on these four contrasting tidal flat and salt-marsh ecosystems indicated that the hydrodynamic forcing on the bottom sediment (bed shear stress) was strongly influenced by wind-generated waves, more so than by tidal- or wind-drive currents. The measurements further showed that the hydrodynamic forcing decreased considerably landward of the marsh cliff, highlighting a transition from vigorous (tidal flat and pioneer zone) to sluggish (mature marsh) fluid forcing. Spatial wave modeling using measured wind, revealed that the time-integrated wave forcing on the intertidal mudflat in front of the marsh (i.e., the potential bed sediment pickup) was a factor two higher for salt marshes that are laterally shrinking than for laterally expanding marshes, regardless of whether these marshes were exposed to or sheltered from the wind. The same result could not be obtained from a straightforward wind speed and fetch length approach for estimating wave forcing. This confirmed that wave force estimates required spatial modeling to be consistent with the sites trends of shrinking or expanding marshes and wind exposure is not enough to characterize the wave forcing at these sites. Seasonal changes in wave forcing identified from wind measurements potentially provide an alternative mechanism for marsh cliff formation. During the calm summer, fine sediments switches from the water column to the bed. During the following winter, fine sediment is retained within the vegetated regions while being returned to the water column from the bare tidal flats. The continuous slow upward growth of vegetated a

Successful management and restoration of coastal vegetation requires a quantitative process-based understanding of thresholds hampering (re-)establishment of pioneer vegetation. We expect scouring to be important in explaining the disappearance of seedlings and/or small propagules of intertidal plant species, and therefore quantify the dependence of scouring depend on plant traits (flexibility, size) and physical forcing by current velocity. Flume studies with unidirectional flow revealed that scouring around seedlings increased exponentially with current velocity and according to a power relationship with plant size. Basal stem diameter rather than shoot length was found to be the factor controlling scouring volume. Flexible shoots caused far less scouring than stiff shoots, provided that the bending occurred near the sediment surface as was the case for Zostera, and not on top of a solid tussock base as we observed for Puccinellia. Therefore, shoot stiffness is likely to strongly affect the chances for initial establishment in hydrodynamically exposed areas. Plant traits such as shoot stiffness are subject to a trade-off between advantages and disadvantages, the outcome of which depends on the physical settings., Successful management and restoration of coastal vegetation requires a quantitative process-based understanding of thresholds hampering (re-)establishment of pioneer vegetation. We expect scouring to be important in explaining the disappearance of seedlings and/or small propagules of intertidal plant species, and therefore quantify the dependence of scouring depend on plant traits (flexibility, size) and physical forcing by current velocity. Flume studies with unidirectional flow revealed that scouring around seedlings increased exponentially with current velocity and according to a power relationship with plant size. Basal stem diameter rather than shoot length was found to be the factor controlling scouring volume. Flexible shoots caused far less scouring than stiff shoots, provided that the bending occurred near the sediment surface as was the case for Zostera, and not on top of a solid tussock base as we observed for Puccinellia. Therefore, shoot stiffness is likely to strongly affect the chances for initial establishment in hydrodynamically exposed areas. Plant traits such as shoot stiffness are subject to a trade-off between advantages and disadvantages, the outcome of which depends on the physical settings.