Westerschelde Research Articles

Beyond the sum

This study presents a multiproxy palaeodemographic perspective by combining radiocarbon dates with counts of archaeological site phases in the western Scheldt basin, spanning from the beginning of the Neolithic to the Early Bronze Age. The results were assessed critically, accounting for differences in research methodology, soil conditions and changes in building traditions. The results indicate a dynamic region characterized by almost continual growth. Moreover, two distinct sub-regions of the basin could be compared, thereby elucidating the sub-regional differences. It is clear that palaeodemographic studies are only feasible when a multiproxy analysis is used on a detailed, highly scrutinized dataset.

Global path planning for inland vessels based on fast marching algorithm

Ship path planning is essential for enhancing navigation safety, shipping efficiency, cost savings and autonomy. This paper presents a path planning algorithm specifically designed for inland vessels, exemplified on the Western Scheldt waterway area from Hansweert to Bath in the Netherlands (known as the area of Schaar van Valkenisse). The algorithm utilizes the fast marching (FM) method to generate safe and cost-efficient paths for both autonomous and conventional navigation, considering factors such as water depth, distance to waterway borders, preferential navigation zones (e.g. starboard side and parallel routes), ship dimensions, and manoeuvring characteristics.The fast marching algorithm uses starting points and a velocity grid, generated based on the aforementioned factors, to produce an arrival time map. The velocity here represents preferences for deeper water, and wider and starboard navigation zones. Subsequently, a gradient descent algorithm is applied to determine the fastest route from the destination to the starting point on the arrival time map. To ensure the route is navigable, the optimal path is updated to a Dubins path that satisfies the ships’ dynamic constraints by using a so-called Dubins model filter.Case studies with various navigation scenarios demonstrate that the path planning tool can provide expected results with tunable parameters allowing for customized preferences. This work can further assist in predicting paths for a traffic study, designing fairways, aids to navigation and can possibly serve as an operational tool to assess the accessibility of a (alternative) fairway.

Exploring the Holocene rise, disturbance and decline of pine forests in the river valleys of northeastern Belgium using pollen and botanical macroremains

The Holocene evolution of vegetation and environment in the Kleine Nete valley in the coversand region of northeastern Belgium is studied through sedimentological, palynological and macrobotanical analysis of a radiocarbon dated peat sequence. Peat formation started at the beginning of the Holocene in mesotrophic fen conditions. After a period of fast peat growth, the accumulation slowed down and the peat surface became dry in the Middle Holocene.The palynological results are compared with other pollen data from the region, in order to establish a regional pollen biozonation for the Early and Middle Holocene in the Nete Basin. This shows that pine has long been a characteristic element in the Nete Basin. Pine forest expanded immediately after the 11.4 cold event, which is earlier than in the western Scheldt Basin. Pine and birch grew along the valley, possibly also within the peatland. Peaks of microcharcoal, herbs and/or coarse sediment in the peat reflect temporary local forest disturbances in the Early Holocene. Some may reflect small-scale controlled fires induced by hunter-gatherers, although a natural cause seems much more plausible given the dominance of fire-associated pines and increased drought. Pine remained important throughout the Early Holocene. This long-lasting predominance of pine in the Nete Basin, compared to elsewhere in the Scheldt Basin, is likely related to the poor sandy subsoil in the region, which hinders more nutrient-demanding broadleaf trees to overtake.

Predicting ecotopes from hydrodynamic model data: Towards an ecological assessment of nature-based solutions

Estuaries worldwide are of substantial ecological value due to the presence of various gradients, such as salinity. Preserving the natural value of estuaries is vital for meeting the climate stabilization goals of the Paris Agreement. Recognizing nature as a stakeholder is imperative, given the surpassing value of ecosystem services over global gross domestic product. Quantifying the current ecological state and future ecological shifts faces challenges, including variable dependencies, spatial-temporal disparities, and the limitations in available information. This study introduces EMMA (Ecotope-Map Maker for Abiotics), a method for quantifying the effects of human interventions or climate change scenarios on estuarine ecosystems by linking abiotic characteristics derived from a hydrodynamic model to ecotopes. The Western Scheldt, an estuary connecting the Scheldt river to the North Sea in the Netherlands, serves as a case study. The method successfully reproduced an existing ecotope-map, which is dependent on real-time data such as aerial photographs. The developed method not only proves applicable in assessing the current ecological state and future ecological shifts for hypothetical scenarios but also demonstrates utility in predicting future situations, providing valuable insights for decision-makers in estuarine ecosystem management and contributing to climate and environmental preservation goals.

The shape of fringing tidal flats in engineered estuaries

For the management of estuaries and the preservation of tidal flats it is crucial to understand the tidal flat shape and development. Previous work focused predominantly on the quasi-equilibrium shape of tidal flats along open coasts with a dominant cross-shore flow and wave exposure. This paper evaluates the shape of fringing tidal flats in engineered estuaries, where longshore velocities generally dominate. Using a long-term (20 years) topographic data set of an anthropogenically modified estuary in the Netherlands (the Western Scheldt estuary), we relate key profile shape parameters and changes over time to natural and anthropogenic processes. In an engineered estuary, the tidal flat shape depends on the estuary geometry, hydrodynamic forcings and human interventions. In contrast to open coast tidal flats, the presence of the channel and dominant longshore flow determines the available cross-shore length (accommodation space) of the tidal flat and the shape of the tidal flat. This accommodation space defines the maximum tidal flat height and opportunity for marsh development. We propose the use of the Index of Development, indicating to what extend tidal flats have space to develop. This index is not only influenced by longshore and cross-shore flow, but also (or even more) by hydraulic structures, dike realignments and channel migration. Especially the latter two strongly influence the accommodation space and thereby the maximum tidal flat height and the opportunity for marsh development. For large stretches of the Western Scheldt, the accommodation space is too small, and the majority of the tidal flats do not vertically extent to mean high water. The success of tidal flat and marsh restoration projects depends on the accommodation space.

A vertebra of a small species of Pachycetus from the North Sea and its inner structure and vascularity compared with other basilosaurid vertebrae from the same site.

In the Western Scheldt Estuary near the Belgian-Dutch border, middle to late Eocene strata crop out at the current seafloor. Most vertebrae of large Eocene basilosaurid taxa from this area were previously described in several papers. They represent three morphotypes: elongated vertebrae of a large species of Pachycetus (Morphotype 1b), a not-elongated vertebra of a large 'dorudontid' basilosaurid (Morphotype 2) and 'shortened' vertebrae of a new, unnamed taxon (Morphotype 3). This article deals with a still undescribed, smaller vertebra, NMR-16642, from this site. Our first aim was to date it by dinoflagellate cysts in adhering sediments. Yielding an age of about 38 Ma, it is one of the very few remains of basilosaurids from Europe, of which the age could be assessed with reasonable certainty. The vertebra, Morphotype 1a, is assigned to a small species of Pachycetus. High-quality CT scans are used to differentiate between NMR-16642, Morphotype 1a, and the large species of Pachycetus, Morphotype 1b. Another aim of this paper is to investigate the inner structure and vascularity of the study vertebra and that of the other morphotypes (1b, 2, 3) from this area by using high-quality CT scans. Notwithstanding differences in size, shape and compactness, the vertebral inner structure with a multi-layered cortex of periosteal bone, surrounding two cones of endosteal bone appears to be basically similar in all morphotypes. Apparently, this inner structure reflects the ontogenetic vertebral growth. An attempt to reconstruct the vascularity of the vertebrae reveals a remarkable pattern of interconnected vascular systems. From the dorsal and, if present, ventral foramina, vascular canals are running to a central vascular node. From this node a system of vascular canals goes to the epiphyseal ends, giving rise to separate systems for cortex and cones. It is the first time that the vascularity of vertebrae of archaeocetes is investigated.

The changing role of hazelnuts (Corylus avellana) in the Mesolithic diet: The Scheldt basin (W Belgium) as a case-study

Hazelnuts were an important foodstuff for Early to Mid-Holocene (Mesolithic) hunter-gatherers all over North-western and Central Europe, mainly thanks to their high fat content, the fact that they are easy to collect and process and produce high areal yields. Based on an extensive and well-dated dataset of charred hazelnut shells, collected on Mesolithic camp-sites from the western Scheldt basin (W Belgium), in this paper the availability of this food resource is studied. Unlike other North(west) European regions, the decline in the exploitation and consumption of hazelnuts in the Scheldt basin appears to start early, from the mid-Boreal period onwards. The available high-resolution pollen and anthracological records indicate that this is presumably related to the rapid and substantial expansion of oak, creating a shady environment which was less favourable for hazel. This paper further examines the impact as well as the possible response of Mesolithic hunter-gatherers to this drastic change in subsistence resources, which arose on top of other challenges during the Boreal, such as increased drought and forest fires, abrupt cooling around 9.3 ka and the possible influx of groups from the adjacent drowning North Sea basin. Human responses possibly ranged from increased mobility, over intensified exploitation of other edible plants to increased fish consumption. The paper ends with emphasizing the importance of high-resolution paleoecological studies on a local/regional level as well as the systematic fine-meshed recovery of plant remains, such as charred hazelnut shells, from archaeological sites.

Comparison of methods for the radiological impact assessment of aquatic releases to the waters in the low countries

Accurate assessment of the radiological impact of liquid discharges on the marine environment is challenging despite all developments in recent years. The lack of consensus on this type of assessment manifests itself even stronger when transborder issues are expected, such as in the Low Countries. Belgium and the Netherlands operate nuclear power plants with discharges in the shared estuary of the Western Scheldt, therefore if there are safety concerns, information on both sides of the border must be coherent. This work provides a comparison of two computational methods used for assessment of aquatic releases in the Western Scheldt estuary and the adjacent North Sea.The work demonstrates a fair degree of consistency in modelling the uptake and fate of key anthropogenic radionuclides. Nevertheless, there are also considerable differences found in sediment and sea species with concentrations ranging by over two orders of magnitude in some cases. These explainable differences are methodological in nature, occurring in codes that underwent extensive validation during development. Therefore, the outcomes of this work clearly demonstrate the need to produce explicit guidance that is specifically tailored to the (inter)national water system of concern. This should not be limited to releases from nuclear power plants, but also include other nuclear applications. For all these reasons, more intensive collaboration and model harmonisation across borders is essential, signalling the direction for future investigations.

Sediment resuspension enhances nutrient exchange in intertidal mudflats

Intertidal coastal sediments are important centers for nutrient transformation, regeneration, and storage. Sediment resuspension, due to wave action or tidal currents, can induce nutrient release to the water column and fuel primary production. Storms and extreme weather events are expected to increase due to climate change in coastal areas, but little is known about their effect on nutrient release from coastal sediments. We have conducted in-situ sediment resuspension experiments, in which erosion was simulated by a stepwise increase in current velocities, while measuring nutrient uptake or release in field flumes positioned on intertidal areas of a tidal bay (Eastern Scheldt) and an estuary (Western Scheldt). In both systems, the water column concentration of ammonium (NH4+) and nitrite (NO2−) increased predictably with greater erosion as estimated from pore water dilution and erosion depth. In contrast, the phosphate (PO43−) dynamics were different between systems, and those of nitrate (NO3−) were small and variable. Notably, sediment resuspension caused a decrease in the overlying water PO43− concentration in the tidal bay, while an increase was observed in the estuarine sediments. Our observations showed that the concentration of PO43− in the water column was more intensely affected by resuspension than that of NH4+ and NO2−. The present study highlights the differential effect of sediment resuspension on nutrient exchange in two contrasting tidal coastal environments.

Annual biogeochemical cycling in intertidal sediments of a restored estuary reveals dependence of N, P, C and Si cycles to temperature and water column properties

Estuarine intertidal sediments are important centres for organic matter remineralization and nutrients recycling. Nevertheless, there is limited understanding regarding how these processes occur along the salinity gradient and their seasonality. Here, we report on the seasonal biogeochemical cycles from three types of intertidal sedimentary habitats (freshwater, brackish and marine) located in the Western Scheldt estuary (The Netherlands and Belgium). A full year of solute fluxes, porewater nutrient and sediment pigment concentrations at a monthly resolution revealed clear differences in the biogeochemistry of the three sites, indicating that environmental conditions determined the local nutrient dynamics. Temperature controlled sediment oxygen consumption rates and nutrient fluxes, but also affected pore water nutrient concentrations up to 14 cm deep. Fresh and brackish sediments had a net influx of dissolved inorganic nitrogen (DIN) (−1.62 mmol m−2 d−1 and -2.84 mmol m−2 d−1, respectively), while only the freshwater sediments showed a net influx of phosphate (−0.07 mmol m−2 d−1). We estimated that intertidal sediments remineralized a total of 10,000 t C y−1, with 97% of mineralization occurring in the brackish and marine parts. Overall, sediments removed 11% (1500 t N y−1) and 15% (∼200 t P y−1) of the total nitrogen and phosphorus entering the estuary from riverine input. Moreover, observations revealed the historical improvement of water quality resulting from water treatment policies. This spatiotemporal study of OM remineralization and early diagenesis in estuarine systems highlights the importance of intertidal sediments for estuarine systems. Our observations can be used in models to predict estuarine biogeochemistry or assess climate change scenarios.

Large-scale morphological changes and sediment budget of the Western Scheldt estuary 1955–2020: the impact of large-scale sediment management

Abstract In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human–sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m3. The highest sediment imports occurred between 1980–1994 and 2005–2020 (2.9 and 3.7 million m3/year). A 1.3 million m3/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, large-scale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of the Western Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide.

Breaching and liquefaction in subaqueous retrogressive flow slides

Although retrogressive flow slides in subaqueous sandy slopes can be very large and cause substantial damage, the failure mechanisms of such slides are not very clear yet. This study analyses two well-monitored flow slides in a shoal margin in the Western Scheldt estuary in the Netherlands: a natural flow slide that eroded 300 m into the edge of the shoal and an artificially induced flow slide that was triggered by dredging and eroded only 30 m of the shoal margin. Both slides were simulated with a newly developed numerical model that describes the physics of slow retrogressive breaching and the much faster retrogression of statically liquefied fine to medium (silty) sands. The simulations show that the differences in trigger and size can be explained by assuming that in the larger slide both retrogressive breaching and static liquefaction took place, while in the smaller one only breaching occurred. The main contribution of retrogressive liquefaction to the larger slide was the generation of a temporary high-erosive density flow that proved sufficient to create such a high, near-vertical slope that the breaching process could continue over a long period and distance. It is therefore likely that both breaching and static liquefaction play a role in large natural flow slides.

Satellite-Derived Trends in Inundation Frequency Reveal the Fate of Saltmarshes

Some of the world’s coastal saltmarshes experience loss in area due to environmental changes, such as relative sea level rise and limited sediment supply. We use satellite remote sensing to assess changes in inundation (flooding) frequency in tidal basins and investigate the bio-physical interactions with saltmarshes. We apply a simple automated method to retrieve time series of inundation frequency change and seaward habitat change of saltmarshes and tidal flats from Landsat-5 TM satellite imagery between 1985 and 2011, for a number of contrasting tidal basins (estuaries, deltas) globally. We evaluated the satellite-derived information on inundation frequency with such information obtained from elevation and tide gauge data for the Western Scheldt estuary, showing good agreement. Application of the method on all study sites reveal which tidal basins are stable or net emerging and which tidal basins are net drowning, but also show large spatial variation in the changes in inundation frequency within each basin. Tidal basins experiencing an overall significant increase in inundation frequency (Mississippi Delta and Venice Lagoon) were associated with an overall loss of saltmarsh area. Satellite-derived temporal and spatial information on inundation frequency helps to assess the fate of saltmarshes in light of sea level change, changes in sediment supply and subsidence.

Transitional polders along estuaries: Driving land-level rise and reducing flood propagation

Dikes are the conventional means of flood defence along rivers and estuaries. However, dikes gradually lead to the superelevation of waterbodies compared to the subsiding embanked areas, resulting in a rapidly increasing unstable situation under sea-level rise. Therefore, future flood management requires new, sustainable strategies that not only minimise flood risk, but also steer land-level rise. An example is a transitional polder, where a dike-protected area is temporarily reopened to the tide to capture sediment until it has risen well above mean sea-level, after which it could be returned to its original function. This study explores how the sequence of opening transitional polders affects sediment capture and large-scale estuary dynamics through 2D modelling in Delft3D. To this end, different opening sequences were tested along a large estuary, using the Western Scheldt (NL) as an example. Findings show land-level rise in all permutations. However, polders opened later in an opening sequence temporarily experience a lag in muddy sediment capture, most likely due to a deficit in fines. Opening more upstream located polders alone or at the start of an opening sequence generally causes a stronger reduction in mean tidal range than opening more downstream located polders. This is explained by increased friction due to (1) locally added intertidal width and (2) shallowing of the main channels because of increased flood dominance. An upstream-to-downstream opening sequence caused the greatest reduction in mean tidal range, but this is negligible compared to the increase in tidal range due to historic dredging within the estuary for navigational purposes. Further work is needed to determine how dredging, closure of transitional polders and storm surges may negate this benefit to flood safety.

Observed and modelled tidal bar sedimentology reveals preservation bias against mud in estuarine stratigraphy

AbstractMud plays a pivotal role in estuarine ecology and morphology. However, field data on the lateral and vertical depositional record of mud are rare. Furthermore, numerical morphodynamic models often ignore mud due to long computational times and simplifications of mixed depositional processes. This study aims to understand the spatial distribution, formative conditions and preservation of mud deposits in the intertidal zone of bars in high‐energy sand‐dominated estuaries, and to elucidate the effects of mud on morphology, ecology and stratigraphic architecture. To meet these objectives, field data (historic bathymetry, bio‐morphological maps and sediment cores of the shoal of Walsoorden, Western Scheldt estuary, the Netherlands) were combined with complementary hydro‐morphodynamic numerical modelling (Delft3D). Based on the field observations, two types of mud deposits were distinguished: (1) mudflat deposits, which are thick (>10 cm) mud beds at the surface associated with high elevations and low accumulation rates; and (2) mud drapes, which are thin (millimetre to centimetre) buried laminae that form and preserve at a wide range of elevations and energy conditions. Model results show that deposition on mudflats occurs just after high‐tide slack water in areas shielded from high flood velocities, suggesting that mud accumulation is mostly controlled by elevation, flow velocity and flow direction. Mud accumulation increases shoal elevation, sometimes to supratidal levels. This reduces flow over the shoal, which in turn reduces chute channel formation, stabilises bar morphology and decreases local tidal prism. These effects further promote mud deposition and vegetation settling. Although observations show that mud cover at the surface is relatively high (20%–40% of the intertidal area), mud constitutes only a small percentage of the total estuary volume (ca 5%) revealing that only a small fraction is preserved in the stratigraphy. Due to this mismatch between surface and subsurface expression of mud, interpretations of estuarine stratigraphy risk underestimating the influence of mud at the surface on morphodynamics and habitats.

AUTONOMOUS SHIP CONTROL IN SHALLOW AND CONFINED WATER

The paper describes the definition and usage of autonomous ship control systems in shallow and confined water. The application of such control system is shown in a case study : a systematic analysis of ship transits in the approach channel to the Port of Antwerp (Western Scheldt) .The control algorithm not only is capable of correctly navigating the ship through the fairway, it also delivers insight in rudder and propeller usage in function of the tidal conditions. Such control systems are validated based on model tests carried out in towing tanks. Flanders Hydraulics Research (FHR) has recently inaugurated their second towing tank, the Towing Tank for Manoeuvres in Shallow Water. One of the functionalities of this facility is the role it can play as test basin for autonomous shipping. Next to the further validation and expansion of existing control scenarios, it will be used to model interaction events between multiple ships. A numerical effort to model interaction events is presented, which will be validated in the model test basin.

Contrasting behaviour of sand and mud in a long‐term sediment budget of the Western Scheldt estuary

AbstractUnderstanding trends in estuarine sediment fluxes is of great interest to sustainable estuarine management addressing anthropogenic interferences and climate change. The long‐term sediment budget of the Western Scheldt estuary, Netherlands, is investigated by a detailed analysis of a unique and long‐term bathymetric data set and data of a three‐dimensional subsurface model (‘GeoTop’). Different sediment types show contrasting transport behaviour. The Western Scheldt narrowed and deepened, while the estuary exported sand (1.5 to 2.5 million m3 per year) and imported mud (0.5 to 1.5 million m3 per year) over the 1860 to 1955 period. The eroded sand originated from the channels in the seaward part of the estuary and was dispersed in all directions. A significant amount of mud permanently deposited in the side branches, which were also gradually reclaimed. These results suggest that sediment characteristics potentially play a crucial role in deriving long‐term sediment budgets and morphodynamic behaviour of estuarine environments. Future morphodynamic sand–mud model studies may reproduce and further explain the underlying transport processes of the current study.

Where and why do creeks evolve on fringing and bare tidal flats?

Although tidal flats appear homogeneous from a distance, morphological variations are found on various spatial scales. These are driven by physical and/or biological processes. In this paper, we consider the creeks that are present on fringing tidal flats and which are orientated approximately perpendicular to the main channel. To explain why these creeks occur, we analysed high-resolution aerial pictures and yearly measured LiDAR data of the Ems-Dollard and Western Scheldt estuaries, located in the Netherlands. We selected nine bare fringing tidal flats, with and without creeks in both estuaries. Subsequently, we related the flat shape to the creek occurrence by evaluating cross-sections of tidal flats from the two estuaries. Finally, we studied how the flat shape affects the cross-shore flow velocity with a 1D numerical model to link creek occurrence to tidal flow. The results show highest ebb velocities, the largest velocity gradients and the largest erosion potential at the transition area between the lower and the upper flat. The milder the slope of the upper flat and the shorter the transition zone, the larger the flow velocities. Based on the data analysis and numerical model outcomes, we conclude that the conditions are favourable for creeks on convex-up intertidal flats with a sharp transition between the upper part and lower part of the flat and that they are predominantly found in this transition zone. We finally argue that these tidal creeks are not only a consequence of the tidal flat profile, but also affect the (equilibrium) profile of the tidal flat.

Facilitating Salt Marsh Restoration: The Importance of Event-Based Bed Level Dynamics and Seasonal Trends in Bed Level Change

Intertidal salt marshes provide a range of valuable ecosystem services which typically increase with marsh width. Understanding the drivers for salt marsh expansion versus retreat is thus key to managers. Previous research highlights the influence of short-term (daily/event) bed level dynamics on germination and establishment and subsequent vegetation presence. However, more recent literature suggests the importance of medium-term seasonal bed level dynamics on viable seed availability and subsequent vegetation presence. This study aims to assess event-based and seasonal bed level dynamics for vegetation presence in natural and semi-natural salt marshes and to provide generic thresholds for vegetation presence. To gain insight into bed level dynamics, data was used from autonomous Optical and Acoustic Surface Elevation Dynamics sensors (O-SED and A-SED) around the edge of natural and semi-natural salt marshes. Sensors were installed at vegetated and unvegetated measurement station Field observations from 22 O-SEDs deployed at 4 well-established natural salt marshes in the Western Scheldt estuary and 4 O-SEDs at a well-established semi-natural salt marsh in the Wadden Sea were reanalyzed. Six novel A-SEDs were deployed at a pioneer semi-natural salt marsh in the Ems-Dollard Estuary. The measurement duration at all salt marshes was at least 1 year. The A-SED sensor was successfully validated against manual measurements. Furthermore, vegetation data and water level data were obtained. No significant difference was observed between natural and semi-natural salt marshes. However, a significant difference between vegetated and unvegetated measurement stations for short-term bed level dynamics was observed. Vegetation was found to be present at locations restricted by short-term bed level variability smaller than or equal to 12 mm, emphasizing the presence of a short-term threshold. Although trends in the non-growing season were significantly different between vegetated and unvegetated stations, seasonal thresholds for vegetation presence were not found. The findings imply that knowledge of bed level-dynamics in well-established natural marshes can be used to predict vegetation presence in constructed semi-natural marshes. The importance of local short-term dynamics for vegetation presence instead of longer-term dynamics highlights possibilities for developing favorable conditions for vegetation presence in marsh restoration projects and the construction of new salt marsh ecosystems.

Hindcasting Ecosystem Functioning Change in an Anthropogenized Estuary: Implications for an Era of Global Change

Understanding how altered hydrodynamics related to climate change and anthropogenic modifications affect ecosystem integrity of shallow coastal soft-sediment environments requires a sound integration of how species populations influence ecosystem functioning across heterogeneous spatial scales. Here, we hindcasted how intertidal habitat loss and altered hydrodynamic regimes between 1955 and 2010 associated with geomorphological change to accommodate expansion in anthropogenic activities in the Western Scheldt altered spatial patterns and basin-wide estimates of ecosystem functioning. To this end we combined an empirically derived metabolic model for the effect of the common ragworm Hediste diversicolor on sediment biogeochemistry (measured as sediment oxygen uptake) with a hydrodynamic and population biomass distribution model. Our integrative modeling approach predicted an overall decrease by 304 tons in ragworm biomass between 1955 and 2010, accounting for a reduction by 28% in stimulated sediment oxygen uptake at the landscape scale. Local gains or losses in habitat suitability and ecosystem functioning were primarily driven by changes in maximal current velocities and inundation regimes resulting from deepening, dredging and disposal practices. By looking into the past, we have demonstrated how hydro- and morphodynamic changes affect soft-sediment ecology and highlight the applicability of the integrative framework to upscale anticipated population effects on ecosystem functioning.