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Increased pressures from human activities may cause cumulative ecological effects on marine ecosystems. Increasingly, the study of ecosystem services is applied in the marine environment to assess the full effects of human activities on the ecosystem and on the benefits it provides. However, in the marine environment, such integrated studies have yet to move from qualitative and scorebased to fully quantitative assessments. To bridge this gap, this study proposed a 4-tiered method for summarizing available knowledge and modelling tools to aid in quantitative assessments of ecosystem services supply. First, the ecosystem functioning mechanisms underlying the supply of services are conceptually mapped. Second, the impacts of the human activity of interest are summarized and linked to the first conceptual model in a case-specific model of ecosystem services supply. Third, indicators are selected that would best represent changes in the most important parameters of the conceptual model in a quantitative manner. Fourth, the knowledge gained in the previous steps is used to select models that are most useful to quantify changes in ecosystem services supply under the human pressure of interest. This approach was applied to the case study of offshore wind energy in the Belgian part of the North Sea, which is one of the most rapidly expanding industries in the marine environment globally. This study provides a useful tool to proceed towards quantification of marine ecosystem services, highlighting the need for a fully integrated approach to developing environmental impact assessment tools.

We studied how changing human impacts affected phytoplankton dynamics in the freshwater and brackish tidal reaches of the Zeeschelde estuary (Belgium) between 2002 and 2018. Until the early 2000s, the Zeeschelde was heavily polluted due to high wastewater discharges. By 2008, water quality had improved, resulting in lower nutrient concentrations and higher oxygen levels. Since 2009, however, increased dredging activities resulted in altered hydro-dynamics and increased suspended sediment concentration. The combined effects of these environmental changes were reflected in three marked transitions in phytoplankton community composition. Assemblages were dominated by Thalassiosirales and green algae (especially Scenedesmaceae) until 2003. The period 2003-2011 was characterized by the wax and wane of the centric diatoms Actinocyclus and Aulacoseira, while in the period 2012-2018 Thalassiosirales and Cyanobacteria became dominant, the latter mainly imported from the tributaries. Phytoplankton biomass increased sharply in 2003, after which there was a gradual decline until 2018. By 2018, the timing of the growing season had advanced with about one month compared to the start of the study, probably as a consequence of climate warming and intensified zooplankton grazing pressure. Our study shows that de-eutrophication (during the 2000s) and morphological interventions in the estuary (in the 2010s) were dominant drivers of phytoplankton dy-namics but that the main shifts in community composition were triggered by extreme weather events, suggesting sig-nificant resistance of autochthonous communities to gradual changes in the environment.

This report is compiled on request of the Maritieme Toegang and has the goal of evaluating a proposed critical nitrogen (N) load to the Scheldt brackish tidal marshes, defined as the N load above which “there is a risk that the quality of the habitat will be significantly affected by the acidifying and/or eutrophicating influence of atmospheric nitrogen deposition”. The present document consists of two main sections: in the first, the proposed nitrogen threshold is evaluated; in the second, a nitrogen mass-balance for brackish tidal marshes is constructed, based on a) available literature from comparable estuaries and b) data obtained from the Scheldt. The magnitude of the pools and fluxes of nitrogen in brackish tidal marshes and its transformations is then evaluated and compared to the proposed critical N load. Most N pools and fluxes in brackish tidal marshes (and in the Scheldt in particular) are in the same order of magnitude or regularly exceed the proposed threshold. This could indicate that estuaries in Europe are already highly impacted by nitrogen pollution, yet it might also mean that the threshold value itself is inappropriate and was not constructed keeping estuaries like the Scheldt in mind. This report discusses both hypotheses.

Managing sediments, especially from dredging, disposal, nourishments and sand mining is important for the management of estuaries and coastal areas. When implemented in the right way, a sediment management strategy can be qualified as a nature-based solution as it uses the physical processes of erosion and sedimentation to create added value. There is a need for an evaluation of sediment strategies and the habitats that are created for a wider range of objectives than only biodiversity and nature conservation. The concept of ecosystem services provides this broader framework.

It is expected that climate change will cause more frequent extreme events of heavy precipitation and drought, changing hydrological conditions in riverine ecosystems, such as flow velocity, evapotranspiration (drought) or runoff (heavy precipitation). This can lead to an increased input of terrestrial organic matter and elevated levels of dissolved organic carbon (DOC) and CO2 due to degradational processes in water. Consequences for submerged macrophytes, as essential organism group, are still poorly understood. The combined effects of changing flow velocity, DOC and CO2 have not been studied before, so this was tested in a racetrack flume experiment on the macrophyte Berula erecta using a trait-based approach. The plants were exposed to two different flow velocities, two DOC concentrations and two CO2 concentrations in a full factorial design. Apart from individual dose-response tests, two climate change scenarios were tested: a wet scenario simulating heavy precipitation and runoff with high flow velocity, high DOC and CO2 concentrations and a dry scenario simulating evapotranspiration with low flow velocity, high DOC and high CO2 concentrations. Growth rate, biomass, morphology, chlorophyll and nutrient content (C, N, and P) were measured. B. erecta responded strongly to both scenarios. Biomass and the relative growth rate increased and stems were shorter, especially in the wet scenario, and vegetative reproduction (the number of stolons) decreased. In both scenarios, the N content was lower and P content higher than in conditions without climate change. It can be concluded that climate change effects, especially shading by DOC, strongly influence macrophytes: macrophyte abundance will probably be negatively affected by climate change, depending on the macrophyte species and abundance of epiphytic algae. This may have consequences for other components of the aquatic ecosystem.

Anurans from the genus Xenopus have long been used as standard testing organisms and occur naturally in tropical and sub-tropical areas where malaria vector control pesticides are actively used. However, literature on the toxic effects of these pesticides is limited. This review analyses the available data pertaining to both Xenopus and the pesticides used for malaria vector control in order to determine the pesticides that have the greatest potential to influence amphibian health while also identifying gaps in literature that need to be addressed. Amphibian diversity has shown the fastest decline of any group, yet there are still voids in our understanding of how this is happening. The lack of basic toxicity data on amphibians with regard to pesticides is an issue that needs to be addressed in order to improve effectiveness of amphibian conservation strategies. Meta-analyses performed in this review show that, at current usage, with the available acute toxicity literature, the pyrethroid pesticide group could hold the highest potential to cause acute toxicity to Xenopus sp. in relation to the other MVCPs discussed, but the lack of data cripples the efficacy with which meta-analyses can be performed and conclusions made from such analyses. Several studies have shown that DDT accumulates in Xenopus sp. from malaria vector control areas, but accumulation of other MVCPs in frogs is still largely unknown. Through this review we hope to encourage future research into the field of amphibian ecotoxicology and to promote the use of the Xenopus standard model in order to build comprehensive datasets that may be used in amphibian conservation.

Climate change can result in multiple indirect alterations of the environment in riverine ecosystems, due to changes in precipitation and runoff. Flow velocity, concentrations of CO2 and nutrients are thereby expected to change, and consequences of the combination of those effects for macrophytes, a key organism group, are still poorly understood. This was tested in a racetrack flume experiment on macrophyte species Berula erecta, an amphibious species growing fully submerged in the experiment. In a full-factorial design, plants were exposed to two different CO2 concentrations, two nutrient concentrations (N, P and Si) and two flow velocities. Apart from individual dose-response tests, two climate change scenarios were tested: a wet scenario simulating heavy precipitation and runoff with high flow velocity, high CO2 and high nutrient concentrations and a dry scenario simulating evapotranspiration with low flow velocity, high CO2 and high nutrient concentrations. Growth rate, biomass, morphology, chlorophyll and nutrient content were measured. Berula erecta responded strongly to both scenarios. Biomass and relative growth rate increased, leaf BSi content decreased, and especially in the wet scenario macrophytes had shorter stems and formed stolons with new ramets: the plants invested in horizontal growth to avoid hydrodynamic stress. Moreover, the C/N ratio was higher, leading to lower quality of macrophyte tissue as food source, and chlorophyll concentration was lower in the high CO2 treatment. It can be concluded that combined stressors caused by climate change strongly affect macrophytes, which may indirectly have consequences for other organisms of the aquatic ecosystem that depend on macrophytes.

In 2013 verdwenen onverwachts de macrofyten (ondergedoken waterplanten) in grote delen van de Grote Nete. De Vlaamse Milieumaatschappij (VMM) zocht naar de aanleiding van deze verdwijning en naar mogelijkheden om de waterplantenpopulatie te herstellen. Uit dit vooronderzoek kwamen twee plausibele hypotheses naar voren omtrent de oorzaak van het probleem: (1) de aanwezigheid van grote aantallen invasieve Chinese wolhandkrabben die de waterplanten zouden aantasten en groei verhinderen, en (2) de aanwezigheid van een ecotoxicologische stof die de groei van waterplanten zou inhiberen. Dit eindrapport geeft een overzicht van de resultaten van het onderzoek naar de eerste hypothese.

The second coastal safety assay in The Netherlands, reported in 2006, showed that more than 70% of the 24-kilometre-long Wadden Sea dyke on the island of Texel failed to meet safety standards. A refurbishment was executed on 14 kilometres of the dyke, increasing its width and height, and adding a cover layer of grass and asphalt. Along the remaining 3.2-kilometre long section in front of the Prins Hendrik Polder (Section 9), a soft coastal protection design called the Prins Hendrik Zanddijk (PHZD) was realised. A dune and beach sandbody was reclaimed seaward of the dyke, upgrading some 200 hectares of the Wadden Sea area.

De Hedwigepolder, letterlijk en figuurlijk een godvergeten uithoek van Nederland, geprangd tussen het verdronken land van Saeftinge, de Schelde en de Belgisch-Nederlandse grens, werd plots landelijk nieuws in Nederland en voorwerp van een jarenlange discussie tussen Vlaanderen en Nederland en van harde acties tegen het ontpolderen. In het in 2005 gesloten Verdrag tussen het Koninkrijk der Nederlanden en het Vlaams Gewest betreffende de uitvoering van de Ontwikkelingsschets 2010 Schelde-estuarium werd immers afgesproken om in het kader van natuurherstel de Hedwigepolder te ontpolderen, waardoor het weer onderhevig zou worden aan de getijdenwerking en het opnieuw tot een slik- en schorgebied zou kunnen ontwikkelen. Op het eerste zicht lijkt het teruggeven van land aan de zee misschien wel een beetje absurd en zeker in Zeeland waar de desastreuze overstromingen van 1953 bij de oudere bevolking nog een echt trauma is. Het doorsteken van dijken roept die oude herinneringen op en alle daarmee gepaard gaande emoties. Is het hele plan om de Hedwigepolder te ontpolderen dan een absurd idee? Uiteraard niet en in deze bijdrage wil ik ingaan op hoe dit plan is tot stand gekomen en wat we mogen verwachten in het gebied, eens ontpolderd. Het is niet de bedoeling om een gedetailleerd beeld te schetsen van alle procedures, ik wil vooral aangeven hoe dit project past binnen een integrale visie op het duurzaam beheer van het Schelde estuarium.

Implementing ‘Working with nature’ in sediment management means the development of sediment management strategies that are more cost-effective and include additional environmental benefits by supporting the creation of specific habitats. Such a smart sediment strategy may not only improve the status of protected areas and species, but at the same time provides multiple socio-economic benefits, known as ecosystems services. Although ecosystem services is considered a key concept to guide sustainable management, practical tools to apply the concept in an estuarine context were found to be missing. In this paper we introduce a GIS-tool that identifies the benefits from ecosystem services in estuaries and links these to several sediment management measures. The tool allows managers to investigate and demonstrate the effects of different sediment management strategies on the delivery of ecosystem services. State-of-the-art knowledge on ecosystem processes and the relationships with ecosystem services were used to develop the impact calculation rules. Following ecosystem services can be assessed: food production (mussels, shrimp and sole), water quality regulation, flood regulation, raw materials provisioning, navigation, climate regulation, recreation (on-shore, swimming and recreational navigation) and habitat support (for seals, breeding birds and wading birds). The practicability and validity of the tool is tested on a series of smart sediment management strategies in the transboundary Scheldt delta.

In deze studie werd de performantie van de huidige indexen voor macro-invertebraten (de Multimetrische Macro-Invertebraat Index Vlaanderen – MMIF) en fytobenthos (Procentuele Abundantie van Impact Sensitieve en Impact Geassiocieerde Diatomeeën – PISIAD) geëvalueerd voor het Vlaamse watertype polderwaterlopen (P) met opsplitsing in zoete (Pz) en brakke (Pb) polderwaterlopen. Eveneens werd de fysicochemie van zoete en brakke polderwaterlopen met elkaar vergeleken. Op basis van chlorideconcentraties werd vastgesteld dat enkele waterlichamen die aangeduid staan als type Pb zouden moeten behoren tot het type Pz. Hiervoor werd een voorstel tot wijziging geformuleerd. De PISIAD-index bleek onvoldoende te presteren voor beide types. Voor een zinnige verandering in klasseindeling (de renspercentages van IA en IS taxa) werd namelijk geen bewijs gevonden Het werd duidelijk dat de MMIF voor de zoete(re) punten een associatie heeft met de waterkwaliteit. Voor brakke lopen vertoonde de MMIF geen zinvolle correlatie met de fysisch-chemische karakteristieken, maar eveneens werden er geen goede vervangindexen gevonden Er werd aangeraden om meer onderzoek te doen naar soortgemeenschappe in plaats van familie- en genus-gemeenschappen in brakke polderlopen. Vooral het effect van zoutfluctuatie dient hierin te worden meegenomen.

Zowel de Marker Horizons, als de Surface Elevation Table’s en de Marker Palen geven nog steeds aan dat een sterke opslibbing van het gebied gaande is. De trend die in 2014 reed opgemerkt werd, met name de vermindering van de hoeveelheid jaarlijks afgezette sediment, werd verder doorgetrokken in 2015. De verklaring hiervoor is dat de meeste slikken zich niet ver meer onder de gemiddelde hoogwaterlijn bevinden. Verwacht wordt dat de sedimentatiesnelheden de komende jaren nog verder zullen dalen. Voor de vegetatie is dit positief nieuws. Nu al merken we in het noordwestelijke gedeelte van het gebied, het gebied met de laagste sedimentatiesnelheden, een voorzichtige ontwikkeling van de diverse schorvegetaties op. Andere delen hebben anderzijds nog steeds te lijden onder de hoge sedimentatiesnelheden, waardoor vegetaties niet de kans hebben om de stukken te koloniseren. Een aantal algemene tot schaarse schorrensoorten hebben het gebied ondertussen weten te vinden en zetten de eerste stapjes in het kolonisatieproces. Andere zeldzame, maar te verwachten schorrensoorten, hebben het gebied nog niet ontdekt. Dit is niet geheel onlogisch daar de meeste van deze soorten typisch pas verschijnen in de latere successiestadia van de vegetatie. Verwacht wordt dat het dan ook maar een kwestie van tijd is tot de meeste van deze soorten Burchtse Weel weten te koloniseren.

In high-latitude fjord ecosystems, the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web. However, the environmental factors that control the timing and intensity of these spring blooms remain uncertain. In 2013, we studied the spring bloom dynamics in Godthabsfjord, a large fjord system adjacent to the Greenland Ice Sheet. Our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers. A combination of out-fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring (April-May), which supplied nutrient-rich water to the surface layer. This surface water was subsequently transported out-fjord, and due to this circulation regime, the biomass accumulation of phytoplankton was displaced away from the glaciers. In late May, the upwelling weakened and the dominant wind direction changed, thus reversing the direction of the surface water transport. Warmer water was now transported toward the inner fjord, and a bloom was observed close to the glacier terminus. Overall, our findings imply that the timing, intensity, and location of the spring blooms in Godthabsfjord are controlled by a combination of upwelling strength and wind forcing. Together with sea ice cover, the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem.

Deelstudie 9 volgt de ontwikkeling op in estuariene herstelprojecten. Hierbij kunnen we twee types monitoring onderscheiden: onderzoeksmonitoring en projectmonitoring. In Lippenbroek wordt onderzoeksmonitoring verricht in het kader van OMES. In een zeer gedetailleerde proefopzet wordt de ontwikkeling van het gebied opgevolgd, met als doel kennis te vergaren. Lippenbroek is immers het eerste gecontroleerd overstromingsgebied met gecontroleerd gereduceerd getij. Een tweede type van monitoring vormt de projectmonitoring. Deze monitoring is minder intensief en gaat via een aantal sleutelparameters hoe de gebieden evolueren. Binnen OMES worden Bergenmeersen, Burchtse en Bazel opgevolgd.

In recent years, it has become increasingly clear that two-way interactions between organisms and landscape-forming processes play a key role in the evolution of many aquatic ecosystems. To be able to compare sedimentation processes among different environments, a standardized method that is generally applicable is necessary. Current methods are usually designed for one environment only or are unreliable in the presence of vegetation. This paper presents the functionality of a plate sediment trap with a lid in combination with a filter paper, which enables the measurement of sedimentation rates in both permanently subaqueous environments and periodically flooded wetlands. We first present the trap design and demonstrate its functionality. No significant differences were found between replicates, nor was there any indication of a trap size effect on the sedimentation rate. Secondly, we demonstrate its applicability in periodically flooded and permanently subaqueous environments and in the presence or absence of vegetation. It is concluded that the use of a standardized method and equipment makes it possible to compare (bio)geomorphological changes in totally different environments.

Based on an analysis in the frequency domain of the governing equation of oxygen dynamics in aquatic systems, we derive a new method for estimating gross primary production (GPP) from oxygen time series. The central result of this article is a relation between time averaged GPP and the amplitude of the diel harmonic in an oxygen time series. We call this relation the Fourier method for estimating GPP. To assess the performance and accuracy of the method, we generate synthetic oxygen time series with a series of gradually more complex models, and compare the result with simulated GPP. We demonstrate that the method is applicable in systems with a range of rates of mixing, airwater exchange and primary production. We also apply the new method to oxygen time series from the Scheldt estuary (Belgium) and compare it with 14C-based GPP measurements. We demonstrate the Fourier method is particularly suited for estimating GPP in estuarine and coastal systems where tidal advection has a large imprint in observed oxygen concentrations. As such it enlarges the number of systems where GPP can be estimated from in situ oxygen concentrations. By shifting the focus to the frequency domain, we also gain some useful insights on the effect of observational error and of stochastic drivers of oxygen dynamics on metabolic estimates derived from oxygen time series.

Aquatic plants (macrophytes) can have a large effect on river hydraulics and geomorphology. Though, the extent to how plant morphological plasticity actively influences these feedbacks has received little scientific attention. The nymphaeid macrophyte species Nuphar lutea (L.) Smith is characterized by a distinct leaf duality. Floating leaves shade most of the submerged leaves thereby limiting light penetration in the water. Despite their apparent negligible photosynthetic role, submerged leaves of N. lutea remain intact during summer and contribute a significant part to the total biomass. Our results indicate that the submerged leaves are crucial in plant-flow interactions and hence in the engineering potential of the plant, i.e. the capacity to locally reduce flow velocities and to promote sedimentation, including organic matter deposition. Plant individuals growing in running river water were compared to individuals from adjacent oxbow lake water. The number and size of submerged leaves were significantly higher for river standing individuals and the accumulated sediment contained significantly more organic matter, total nitrogen and total phosphorus, and was characterized by a lower carbon/nitrogen ratio and a finer grain size. We therefore argue that the submerged N. lutea canopy in rivers has the ability to create a high-nutrient, low hydrodynamic environment, resembling the conditions found in oxbow lakes. Copyright (c) 2014 John Wiley & Sons, Ltd.

Flood Control Areas (FCAs) are one of the measures to protect the Flemish part of the Scheldt estuary against storm surges. Recently, in some of these FCAs a Controlled Reduced Tide (CRT) was introduced by means of simple sluice constructions, aiming at a combination of flood control with nature development and the ecological functions of intertidal areas. This paper gives an overview of the different types of inlet sluices and energy dissipation measures that have been designed, built and/or are under construction: an inlet sluice with an inclined drop, an inlet sluice with a pooled step cascade and a combined inlet-outlet sluice with an internal drop structure.

The present study evaluated the effect of increasing oxygen concentrations in overlying surface water on the accumulation and toxicity of sediment-bound metals in the aquatic invertebrates Lumbriculus variegatus, Asellus aquaticus and Daphnia magna. A 54 days experiment using three experimental treatments (90% O2 in overlying surface water, 40% O2 and a non-polluted control) was conducted. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured in the superficial sediment layer (01 cm). At each time point, accumulated metal levels as well as the available energy stores were measured in L. variegatus and A. aquaticus and each time D. magna was exposed to surface water in a 24 h toxicity test. Additionally metallothionein-like protein (MTLP) induction was quantified in L. variegatus. Oxygen induced changes in sediment AVS resulted in faster accumulation of metals from contaminated sediments in A. aquaticus, while no differences in toxicity in this species were observed. Ag, Cr, As and Co accumulation as well as toxicity in water exposed D. magna were clearly enhanced after 54 days, caused by oxidation of metal-sulfide complexes. Due to their feeding and burrowing behaviour, metal accumulation and toxicity in L. variegatus was not influenced by geochemical characteristics. Nevertheless, a rapid induction of MTLP was observed in both the 90% O2 and the 40% O2 treatment. The present study showed that elevated oxygen concentrations in overlying surface water can directly enhance metal accumulation and toxicity in aquatic invertebrates, however this is highly dependent on the organisms ecology and most dominant metal exposure route (water vs. sediment).

In order to evaluate the effect of improved oxygen concentrations in overlying surface water on the redox status, sediment geochemistry and metal bioavailability in metal-polluted sediments a 54 days lab experiment with two different experimental treatments was conducted (90% and 40% O2). Changes in redox potential (Eh) in the sediment were monitored over time. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) and at 4 sediment depths (01, 14, 48 and 815 cm), acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured and metal release to overlying surface water was determined. Labile metal species in both water and sediment were measured using Diffusive Gradients in Thin films (DGT). Our results showed that elevated oxygen levels in overlying surface water led to an Eh increase in the sediment of the 90% O2 treatment from 0 to ±200 mV while AVS concentrations in the upper sediment layer decreased by 70%. Following AVS oxidation metal availability in the pore water was highly elevated after 54 days. However, Cu remained strongly bound to the sediment during the whole experiment. Only a limited metal release to the overlying surface water was noticed, which was due to the fact that SEMtot concentrations in the sediment did not yet exceeded AVS levels ([SEMtot − AVS]/fOC = 0) after 54 days. Additionally, adsorption on Fe and Mn hydroxides and particulate organic carbon also slowed down any potential metal release. Our results indicated that increasing oxygen concentrations due to general water quality improvements can enhance the mobility of trace metals which may result in the leaching of sediment-bound metals to overlying surface water, even in undisturbed watercourses.