Effect Chain Modelling to Support Ems-Dollard Management

Transcription

1 Journal of Coastal Research SI MCRR Conference Proceedings 2011 Effect Chain Modelling to Support Ems-Dollard Management Claudette Spiteri 1, Bas van Maren 2, Thijs van Kessel 1 and Jasper Dijkstra 2 2 Deltares; Marine and Coastal Systems Unit, P.O. Box 177, 2600 MH Delft, the Netherlands Delft University of Technology; Faculty of Civil Engineering and Geosciences; P.O. Box 5048, 2600 GA Delft, the Netherlands Tel: claudette.spiteri@deltares.nl 1 Deltares; Marine and Coastal Systems Unit, P.O. Box 177, 2600 MH Delft, the Netherlands ABSTRACT SPITERI, C., VAN MAREN, B., VAN KESSEL, T and DIJKSTRA, J., Effect Chain Modelling to Support EMS-Dollard Managemnt. In: Micallef, A. (ed.), MCRR Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp Grosseto, Tuscany, Italy, ISSN The Ems-Dollard estuary, located at the eastern side of the Dutch Wadden Sea, is influenced by conflicting human demands ranging from flood protection, shipping, ports and dredging activities, nature preservation, energy demands, fisheries, tourism and recreational activities. This combination of pressures jeopardizes the water quality and ecological functioning and demands for an integrated sustainable development plan. As part of the strategic management plan for the area, a so-called effect chain modelling framework is being developed. This process-based approach combines biotic and abiotic processes, the main ecological components and the relevant anthropogenic demands. The integrated modelling framework is implemented in Delft3D (developed by former WL Delft Hydraulics) and is composed of separate building blocks for hydrodynamics (Delft3D-FLOW) and sediment transport (Delft3D-SED), water quality (Delft3D-WAQ/BLOOM) and ecological dynamics (HABITAT) including interactions with higher trophic levels using a GIS-based spatial analysis tool. It allows for the quantification of the impact of a system component, parameter or process on the relevant ecological groups or processes within the marine environment. It results in an improved understanding of cause-effect relationships between the physical, natural environment and system stressors. The ultimate aim of the modelling framework is to develop a robust assessment tool for dealing with management questions related to site-specific issues, such as the relation between high turbidity and oxygen-depleted zones or the effect of nutrient inputs and dredging activities on water quality and habitat suitability. ADDITIONAL INDEX WORDS: coastal management, numerical modeling, hydrodynamics, sediment, water quality, ecology. INTRODUCTION Situated along the North Sea coasts of Denmark, Germany and The Netherlands, the Wadden Sea is one of the world s largest and most important intertidal wetland ecosystems. The Wadden Sea is recognized internationally as an area of major ecological, economic and social importance, attracting more than 10 million annual tourists and million daytrippers. Since 2009, the Dutch and German parts of the Wadden Sea have been inscribed on UNESCO's World Heritage List, whereas the Dutch part is also appointed Natura2000 site. DOI: /SI received XX; accepted XX Coastal Education & Research Foundation 2011 This implies that the primary function of this region is nature and hence exploitation is only allowed if negative effects on the ecosystem are kept to a minimum. On the eastern side of the Dutch Wadden Sea along the border between The Netherlands and Germany lies the Ems- Dollard, the estuary of the Ems River (Figure 1). The Ems- Dollard hosts a unique transition between freshwater, brackish and saltwater habitats and accommodates a large number of species. It serves as a resting, breeding and feeding place for numerous bird species, as well as a nursing ground for fish. A number of salt marshes, formed during the flooding of the mud flats at high tide, can be found in the brackish and tidally-influenced Ems-Dollard region. These mud flats are made of pure sea clay and provide a unique habitat for rare plants. Despite the high ecological value of this region, the Ems-Dollard is at the same time under the influence of multiple anthropogenic activities including navigation, 226

2 Effect Chain Modeling to Support EMS- Dollard Management industry, fisheries and recreation, and various stakeholder interests. The interaction of the natural system and human demands has substantially changed the functioning of the Ems-Dollard estuary in the past years. Turbidity levels have increased significantly, the maximum turbidity zone has widened and shifted further inland, primary production has decreased and the frequency of anoxic events during the summer has increased in the upstream portions of the estuary. 0 km 25 km 40 km 50 km Aa 100 km semi-diurnal with ranges of 2.3 m at the inlet to ~3.5 m in the river. Tidal flats on the side of the channels cover an area of about 50 % of the entire estuary and approximately 80 % in the Dollard sub-basin during low tide. The other dominant physical processes that affect the estuary are wind and freshwater inflow. About 90 % of the freshwater input comes from the Ems River, draining a basin of ~ km 2, with an average discharge of ~ 100 m 3 /s. The Westerwoldse Aa, located in the south-east corner of the Dollard basin (Figure 1), discharges around 12.5 m 3 /s. The functioning of the Ems-Dollard is controlled by the interaction between the natural system and the human impacts, as represented schematically in Figure 2. Being under the shared national jurisdiction of both Germany and The Netherlands, the functioning of this site is also particularly subject to intricate political and management issues. Figure1. Map of Ems-Dollard estuary showing its location at the border of The Netherlands and Germany (modified from De Jonge, 2000). In order to support future management of the Ems-Dollard area, there is a need for a common understanding of the functioning and long term vision on the development. The long-term management of this region demands for a tool that gives more insight in the system functioning by integrating the feedbacks between the hydrodynamic, biogeochemical and ecological components. This so-called effect chain approach combines the complex biotic-abiotic interactions, the main ecological components, including higher trophic levels and the impact of anthropogenic activities within the same assessment. The objectives of this paper are twofold: to provide a comprehensive overview of the multiple anthropogenic pressures and their interaction with the natural functioning of the Ems-Dollard and to present the methodology and application of a process-based modelling tool based on the effect chain approach that integrates the feedbacks between the natural and anthropogenic components. This tool will be later used to address future management questions and to provide a scientific basis for management decisions related to processes that operate at different time and spatial scales. SYSTEM FUNCTIONING The Ems-Dollard is a semi-enclosed estuary stretching from the barrier island of Borkum at 0 km to a dam near Herbrum, 100 km inland (Figure 1). Three main sub-areas can be identified: the Lower, Middle and Dollard reaches. The tide is Figure2. Schematic representation of the system functioning, showing the interaction between components of natural system, human impact, management and political issues Ecology NATURAL SYSTEM In terms of the European Water Framework Directive (WFD), the Ems-Dollard estuary is a transitional water body with a reasonable quality or a reasonable potential, if the estuary would be regarded as a substantially modified area rather than as a natural area. Of the four elements that determine quality, phytoplankton and fish are considered good, whereas plants and macrofauna are labelled reasonable. The small area of salt marshes and the poor condition of seagrass fields are limiting factors, as are the presence and the diversity of benthic fauna. Following Natura2000 habitat-types, the complete Ems-Dollard area belongs in the category H1130-Estuaries. Other habitat-types are H1110-Permanently submerged banks, H1140-Mud and sandflats, H1310-Salty pioneers, H1320-Spartina swards and H1330-Atlantic salt marshes. Dune-related habitats are only present at the bordering islands of Borkum and Rottumeroog. 227

3 Spiteri et al. Each of these habitat-types has important functions for the ecosystem. The estuary provides a transition between salt water and fresh water for diadromous fish, as well as a sheltered food-rich nursing area for juvenile fish that spend their adult life in the North Sea. The submerged banks and tidal flats harbour shellfish and crustaceans, which in turn are a food source for birds and fish and humans. These shallow areas are also home to microphytobenthos, macroalgae, seagrass fields and salty pioneers that can eventually develop into salt marshes where many birds breed and feed. Microphytobenthos play an important role in the total primary production of the Ems-Dollard estuary, in particular of the Dollard basin (De Jonge, 2000), contributing to ~25% to the total annual primary production. Benthic diatoms reach the water column simultaneously with the fine sediment fraction, mainly consisting of sediment aggregates and kept together by organic matter. The combination of haul-out sites and an abundance of fish determine the value of the estuary to marine mammals. Biotic-Abiotic Interactions Most of the management issues concerning the Ems-Dollard are linked to the biotic-abiotic interactions, in particular the effect of increased turbidity on ecological functioning and the formation of fluid mud at sediment concentration higher than 25 g/l. The increase in sediment concentrations in the turbidity maximum in the Ems River from ~100 mg/l in 1954 to ~ mg/l in the 1970 s and 1980 s has led to a 5-10 fold increase in the water column turbidity. This is the result of increased dredging activities related to maintenance dredging and deepening of shipping lanes, combined with the dumping of dredged material. Field measurements in the brackish and freshwater portions of the river Ems show a correlation between high sediment concentrations and anoxic events (Talke et al, 2009) because oxygen dynamics are closely coupled to the location of fluid mud. High turbidity levels also limit primary production in the water column, although the influence on benthic primary production is still under investigation. Populations of microphytobenthos living on tidal flats are exposed to water currents and waves. Diatoms and sediments are eroded from tidal flats at relatively low current velocities, implying that the processes of resuspension, mixing and redeposition are almost instantaneous (De Jonge and van den Bergs, 1987). In this way, hydrodynamics processes can partly control the distribution, abundance and species composition of benthic diatoms in coastal areas. Since the resuspension of the microphytobenthos to the water column is subject to hydrodynamics and more specifically to wind conditions, the ecosystem functioning of such estuaries is closely coupled to abiotic controls. HUMAN IMPACT Human Demands, Functions and Pressures The main anthropogenic activities taking place in the Ems- Dollard basin are shipping, coastal protection through storm surges, water intakes/outfalls, wastewater disposal and fishing (Figure 3). Figure3. Map of Ems-Dollard estuary showing the location of multiple pressures in the area. Harbours and Shipping Routes With 10,000 movements of sea-going vessels and 6,000 movements of inland navigation vessels per year, the Ems- Dollard is an important shipping route. A navigation channel maintained at a navigable depth of 8 m with a maximum depth of ~30 m runs from Borkum to the harbour town of Emden (46 km). The other two important harbours are Eemshaven and Delfzijl. The shipping lane between Emden and the upstream Papenburg (87 km) is maintained at ~7 m depth. The depth of the Ems River has increased from ~ 4-5 m to more than 7 m over the past 20 years, thereby increasing the tidal range by as much as 1.5 m. Yearly dredging in the navigation route of Emden and the harbours of Delfzijl and Eemshaven amounts to 7.2 Mm 3 /yr. Other pressures associated to navigation include noise, shipping accidents, oil spills, ballast water, anti-fouling substances as well as impacts from recreational yachting and sailing. Storm Surge Barrier As a protection against storm surges and flooding, a barrier (Emssperrwerk at 50 km) was built near Gandersum in This barrier is also used to raise the water level in the Ems River in order to facilitate the passage of large ships to and 228

4 Effect Chain Modeling to Support EMS- Dollard Management from the shipyards near Papenburg. Closure is allowed twice a year, for a maximum of 104 hours during the winter. Cooling Water Intake and Outfall With a yearly average discharge of 55 m 3 /s, the current powerplant in Eemshaven, the Eemscentrale, is the major user of cooling water. Plans for expansion with three other powerplants with a combined output of 4 GW would require the intake of cooling water to increase to 163 m 3 /s (van Banning et al, 2008). The ecological consequences of cooling water include the impingement of fish and other organisms during intake and thermal pollution due to the discharge of cooling water. According to Hartholt and Jager (2004), 18 million fish were impinged during intake in 1996/1997, most of them being herring, sprat, gobies and stickleback. The actual effect of cooling systems on populations is more difficult to estimate since most of the impinged fish are young ones. Smaller organisms like phytoplankton, copepods, fish larvae, fish eggs, jellyfish and crustaceans are also taken up. However, their mortality caused during the intake of cooling water is unknown. Brine- and Wastewater Disposal Wastewater disposal led to high concentrations of mercury and anoxic conditions in the Dollard in the past century. Since the 1970 s the quality of the discharged water has improved and is no longer of environmental concern. In the past years, brine from German salt mines has been discharged into the outer area of the estuary. Brine from a soda plant is also discharged near Delfzijl. Fishing Nowadays, fishery in the estuary is less extensive than at the beginning of the 20 th century. The number of fyke-fishing permits decreased sharply in the 1990 s as a result of an abolishment policy, whereas shrimp-fishing is only allowed for Dutch and German locals. Management and Political issues Due to its geographical position, the management of the Ems-Dollard estuary is complex. Despite the 1960 Ems- Dollard Treaty (UN, 1960), the Ems-Dollard still remains a disputed area. In this treaty, Netherlands and Germany agreed to disagree on the boundary in the Ems-Dollard area. The 1962 Supplementary Agreement was an exceptional agreement in that it provided for the equal division of oil and gas reserves between the two countries in an area where no inter-state boundary exists. The Ems-Dollard Environmental protocol in 1996, an additional protocol to the 1960 Treaty, was aimed at increased cooperation on issues related to water management and nature protection. In that same year, Ems- Dollard Regional (EDR) office was also established for strengthening cooperation on regional economic activities, including agro-business, energy, the maritime sector and tourism, with little focus on environmental issues. Since most of the surrounding Wadden Sea is designated as a Particular Sensitive Sea Area under European rules, the benefits from the gas extraction taking place in the area, among others, remains a sensitive issue. In this respect, effective crossborder governance and policy making remains a challenge. Fortunately, in the last decade, German-Dutch cooperation has increased, partly due to the implementation of European directives like Natura 2000, the Birds and Habitats Directive and the Water Framework Directive, as well as a result of European collaborative projects such HARBASINS (Harmonised River Basins North Sea) (HARBASINS, 2008). The nature of the management questions has changed during the history of the Ems-Dollard from past issues related to chemical discharges, including potato waste effluents from the Westerewoldse Aa, to current issues on cooling water discharges. Dredging was, and still remains, the most significant anthropogenic pressure with the tendency of becoming more important with increasing size and capacity of navigation vessels. Future management questions however, do not only concern the impact of increased dredging and cooling water discharges but also involve aspects of climate change, such as the impact of sea level rise. The implementation of alternative management strategies demands for further insight on questions addressing the: Biotic-abiotic interactions: that is the effect of sediment dynamics on ecology? Current system drivers: is primary production nutrient-limited or light-limited? what is the role of microphytobenthos in primary production? Relationship between ecological functioning and human demands Scenarios carrying capacity for higher trophic levels (birds, fish, seals) presence and quality of different habitats effect of climate change Effect Chain Modelling METHODOLOGY One way to combine the assessment of the main ecological components, the biotic-abiotic interactions and the relevant 229

5 Spiteri et al. human demands is through the so-called effect chain modeling approach. The effect chain framework offers an integrative and holistic way to investigate cause-effect relationships between the hydrodynamics, sediment transport, water quality and ecology, as well as interactions with higher trophic levels. This approach presents a process-based tool to support future management decisions. A schematic representation of the components, links and possible relationships in an effect chain modeling framework is given in Figure 4. Figure4. Conceptual outline of the effect chain approach showing interactions between the different building blocks. Public Works and Water Management, containing data on a number of physical and water quality parameters. In the 1970 s, a water quality monitoring programme was initiated (salinity, transparency, extinction, nutrient concentrations, oxygen, chlorophyll-a and suspended sediments) at 33 monitoring stations, which were later reduced to three main locations (Bocht van Watum, Groote Gat Noord and Huibertgat Oost, in the Dollard, Middle and Lower Reach, respectively) Biomonitoring campaigns within The Trilateral Monitoring- and Assessment Program (TMAP) focus on the collection of data on phytoplankton, eelgrass, macroalgae, macrozoobenthos and fish, as part of the surveillance monitoring for WFD. The Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (NLWKN) carries out continuous measurements of salinity, water level, oxygen content and sediment concentration in 8 fixed stations in the Ems River. Data collection started between 1992 and 2001, depending on the station. In addition to these fixed stations, monthly cruises along the Ems River are done to measure turbidity, dissolved organic carbon, total organic carbon, ammonium, nitrate, chlorophyll-a, temperature, conductivity, phosphate and suspended sediment concentration. Although much field data is available, the relationship between the pressures, drivers and impacts remains unclear due to the lack of integrated and coherent data analysis. Within the effect chain approach, data collection and data analysis will serve as the basis for setting-up subsequent models, whereas the results of the modelling framework will help in the optimization of future monitoring requirements. Hydrodynamics: Delft3D-FLOW The proposed layout is divided in four phases: hydrodynamics, sediment, water quality, ecology, showing a step-wise increase in complexity and resolution. Underlying all four components is data collection and monitoring. The aspects of hydrodynamics and sediment are the fundamental parts of the effect chain by determining the light conditions for algal growth and subsequent higher trophic levels. Data Collection and Monitoring A number of Dutch and German monitoring campaigns involving the collection of physical, chemical and biological data have taken and are still taking place. The Donar database ( is a publicly-available and comprehensive database managed by the Dutch Ministry of The water motion is simulated using the Delft3D-FLOW modelling system which solves the equations of motion and momentum using an ADI finite-difference scheme on a curvilinear staggered grid. The model domain is approximately 30 km seaward of the barrier islands (see Figure 5) to the weir at Herbrum (blocking further tidal intrusion). The model grid has 8 vertical layers and is relatively coarse on the seaward boundaries (1000 by 2000 m), but becomes progressively finer towards the areas of interest (down to 50 by 100 m in the Ems River). The tidal boundary conditions are obtained from larger-scale models. Fresh water enters the model through a number of small rivers, but primarily through the Ems River, with an average discharge of around 80 m 3 /s. This freshwater input generates a gravitational circulation resulting in a net landward-directed flow component near the bed and a seaward-directed flow component near the surface. In the Ems estuary, the water is well-mixed to weakly stratified, depending on the Ems discharge. In the Ems River, gravitational circulation is less important due to the shallow water. The tide-topography induced residual flows are large in the Ems estuary. The residual flow velocities are dominated 230

6 Effect Chain Modeling to Support EMS- Dollard Management by the existence of large-scale horizontal circulation cells (De Jonge, 1992) resulting in a seaward increase in the residual flow velocity. Tides are semi-diurnal mesotidal but are amplified, becoming progressively asymmetric in the Ems River. Figure5. Water depth (m below Dutch Ordnance Datum) in the model domain. asymmetry in vertical mixing and flocculation, generating much higher flood transports than ebb transports. As a result, the Ems River now is a very efficient sediment trap in which sediment is continuously accumulating (Winterwerp, 2010). Modelling the sediment-turbulence interactions on seasonal or multi-year timescales is challenging on a process level but also in terms of computational time. Therefore we follow two sediment modelling approaches. Sediment-turbulence interactions are modeled with Delft3D Sediment online (Lesser et al, 2004), which computes sediment transport and morphological update simultaneously with the flow. This model simulates the generation, transport, and dissipation of turbulence with a k- model, in which turbulent mixing is modified by sediment-induced buoyancy effects through the equation of state; see Winterwerp and van Kessel (2003). A dedicated version of this model exists in which flocculation and consolidation processes are implemented (van Maren et al, 2007). This model can be used to analyze detailed transport processes on short timescales. For longer timescales, Delft3D- WAQ is used. This model computes storage of fine sediments under influence of waves and tides as a thin fluff layer on a sandy bed, but also mixed with the sandy substratum (van Kessel et al, 2010). In this way, the seasonal cycle of summer sedimentation and winter erosion can be reproduced. Adding biota effects is part of future work. Sediment transport: Delft3D-SED (Sed-online and Delft3D-WAQ) Sediment mainly enters the Ems Estuary from the seaward side (the North Sea but more importantly from the Wadden Sea) and to a lesser extent from the landward side (the Ems River). Most sediment in the Ems-Dollard estuary and the lower Ems River is of marine origin. The sediment concentration in the Ems-Dollard estuary is typically several 100 mg/l, varying a factor two between spring and neap and a factor two between summer and winter. Summer concentrations are lower because of reduced wave activity and higher biological activity. Concentration minima as a result of biologic effects occur around April when temperatures allow formation of diatom mats covering the tidal flats, but are not yet destroyed by bioturbation. In the Ems-Dollard estuary, sediment is transported upstream by tidal asymmetry and gravitational circulation. In summer this sediment is partly stored on the mudflats in the Dollard, while an additional part is transported further upstream in the Ems River. In winter, the mudflats are eroded and sediment is released into the water column. Transport mechanisms are more complex in the Ems River. Here, the flow velocity is strongly asymmetric (with flood flow velocities up to 2 times the ebb flow velocities), resulting in import of sediment. Due to accumulation of sediments, the sediment concentration in the Ems River now exceeds several 10 s to 100 s of g/l in a 1-2 m thick fluid mud layer. This layer dampens turbulence mixing, which in combination with the flow asymmetry, causes an Figure6. Overview of the substances and processes considered in the water quality model Delft3D-WAQ. Water Quality: Delft3D-WAQ/BLOOM The water quality module of Delft3D suite, Delft3D-WAQ, is used to model nutrient (nitrate, ammonium, phosphate and silicate) dynamics, dissolved oxygen and organic matter through an extensive reaction network that includes mineralisation of organic substances and release of nutrients, sedimentation and resuspension, reaeration of oxygen, nitrification/denitrification, phosphorus sorption/desorption and light extinction (Figure 6). The latter provides a direct link to the output of the sediment module. The module BLOOM models the competition between different algal types and the adaptation by species to limiting 231

7 Spiteri et al. factors such as nutrients and light, by accounting for their growth, respiration and mortality (Los and Wijsman, 2007). The following algal types are considered: flagellates, dinoflagellates, Phaeocystis, suspended and fixed microphytobenthos, freshwater and marine diatoms, green algae and seagrass (Zostera). It is also possible to incorporate additional complexity by computing changes in grazer biomass, such as zooplankton and mussels, subject to growth, maintenance respiration and mortality. Ecology: HABITAT HABITAT is a spatial analysis tool that analyses availability and quality of habitats resulting in a prediction of habitat suitability (Haasnoot and van de Wolfshaar, 2009). HABITAT is suited for estimating potential occurrence of higher trophic levels, such as benthos, birds or marine mammals based on an extensive ecological knowledge database, response curves and decision rules (Figure 7). For instance, in the case of Ems Dollard, it can be used to address questions on the stability and magnitude of tidal flats, fish migration and carrying capacities of higher trophic levels. HABITAT is the last step in the effect chain modelling approach in which the building blocks from the different stages (hydrodynamics, sediment transport, water quality and ecology) are integrated. require the presence of either water- or terrestrial plants. Wellknown individual species are also considered, based either on the high amount of monitoring data available or other aspects of special interest. With respect to plants, the seagrasses in the Ems-Dollard are treated specifically, whereas the plants in higher areas are grouped into the habitats H1310, H1320 and H1330. The main suitability indicators are hydrodynamics, bed level and the management of artificial salt marshes. For fish, Sparling (Osmerus eperlanus) is chosen as one of the key species because it is a well-known anadromic species and it serves as a food source for many birds and larger fish. Adult Sparling is a pelagic piscivore that lives in open, preferably turbid oxygen-rich water. Other categories are benthic visual predators, other benthics, pelagic feeders, for which the main indicators are oxygen, salinity, temperature, turbidity, food availability and connectivity. Only three species of large, marine mammals are indigenous to the Ems-Dollard. All these mammals are sensitive to noise and disturbance, and risk of getting stuck in fishing nets. Pollution and diseases are other threats. Their occurrence depends on food (fish), disturbance and the presence of resting areas. RESULTS The applicability of the effect chain approach is demonstrated with an illustrative example in which the habitat suitability for the indicator species Red-breasted merganser (Mergus serrator) is evaluated. This bird, which dives for fish, prefers clear waters with a depth of less than 3.5 meters. Its occurrence strongly depends on the season, available breeding ground, food (fish, benthos or plants) and underwater visibility. Figure7. Visualisation of the principle of HABITAT: input maps and response curves are combined in a raster-based GIS to produce maps and spatial statistics of habitat suitability. A number of habitat-representative indicator species or groups of species for the Ems-Dollard area has been selected. These groups are, among others, representative of pelagic and benthic, piscivores and herbivores, salt water and fresh water, aerobic and anaerobic organisms Figure8. Example of how the results from the hydrodynamic/sediment/water quality models could be combined in HABITAT to provide a map of Total Habitat Suitability Index (HSI) for the Red-breasted merganser Mergus serrator. Only the middle reaches of the Ems-Dollard are shown. Darker colors indicate a higher suitability. Note that Secchi depth is taken as a measure of turbidity. Piscivores require clear water and fish, benthivores shallow water or intertidal areas with macrofauna and herbivores As shown is Figure 8, the habitat suitability index (HSI) of the Middle Reach in the Ems-Dollard during spring is 232

8 Effect Chain Modeling to Support EMS- Dollard Management estimated by superimposing the water depth and turbidity distributions and applying the response curves established for the habitat suitability of Red-breasted merganser. The water depth for this particular time period is an output of the hydrodynamic model whereas the turbidity is derived from the water quality model. Note that abiotic variables, such as water depth and turbidity can be more accurately predicted than for example, food availability. The resultant HSI map shows those areas characterized by higher habitat suitability (the darker the shade of grey, the higher the suitability). In this particular example, the prerequisite conditions of shallow and clear water hardly coincide spatially in the Middle Reach, implying that in a given location, the water is either too deep or too turbid. Since the different layers used as input to the HABITAT tools are directly coupled to the other model building blocks, HABITAT presents a powerful tool not only for assessing the present-day occurrence of suitable habitats but also to evaluate alternative management scenarios that include the complex interaction between water movements, sediment dynamics and water quality. OUTLOOK In view of the two overarching goals: towards a common understanding of the functioning and towards a common long term vision on the development agreed upon for the future management of the transboundary Ems-Dollard estuary, a comprehensive and harmonized modelling tool is currently being developed. This tool is based on the effect chain approach in which the different system components related to hydrodynamics, sediment transport, water quality and ecology, are integrated within the same framework. Such a building block approach allows for an integrated assessment of complex processes and feedbacks that act on different temporal and spatial scales. This tool will serve as a basis for future decisions related to the integrated management of the Ems-Dollard estuary, an area with changing natural functioning and under the pressure of multi-human functions and demands. One of the main challenging aspects of the effect chain approach is to find the right compromise between the degrees of complexity required in each step to address the related management questions. Future work will focus on the detailed inclusion of the microphytobenthos in the water quality model and the refinement of the suitability indices and response curves for selected species and groups of species. The latter will include, for example, the consideration of factors that are not easily quantified, such as food availability. The integrated modelling framework can be then used to assess the system response to changing forcings in a number of defined scenarios, to optimize the current monitoring strategies and to help design new monitoring campaigns, such as measurements of primary production and benthic production. ACKNOWLEDGEMENTS This work is carried out as part of the Applied Research Programme Eems-Dollard, funded by the Dutch Ministry of Public Works. LITERATURE CITED De Jonge, V.N., Tidal flow and residual flow in the Ems Estuary. Estuarine Coastal Shelf Science 34, pp De Jonge, V.N., Importance of temporal and spatial scales in applying biological and physical process knowledge in coastal management, an example for the Ems estuary. Continental Shelf Research 20, De Jonge, V.N. and J. van den Bergs, Experiments on the resuspension of estuarine sediments containing benthic diatoms. 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