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    System description

    Delta lakes are generally regarded as socio-ecological systems. These are characterized by interactions between humans and the lake ecosystem. On the one hand, riparian societies adapt a lake to their needs and put the ecosystem under pressure, on the other hand these societies respond to the functioning of the lake ecosystem.

    The delineation of a delta lakes is indistinct; it very much depends on the perspective. From a hydrological point of view, one may include or exclude adjacent water bodies or rivers that are discharging into or receiving water from the lake. From an ecological point of view, the delineation can include for example habitat areas far away that are used by migratory birds and fish.

    From a management and governmental perspective, the boundary of the water body is usually considered to be the demarcation line, maybe because of historic reasons, or because of the sharp contrast between the water and the surrounding land.

    An analysis of the socio-ecological system of delta lakes should include insight into:

    • the physical processes
    • the biotic ecosystem processes
    • the interrelations and feedbacks between the biotic and abiotic processes
    • the governance structures and management systems.

    (See tool for system analysis)

    The next paragraphs give an overview of these processes, interactions and structures in delta lakes.

    Ecology of delta lakes

    The biodiversity of delta lakes can differ greatly, not only between delta lakes but also within a single lake. Two key factors that determine the biodiversity in delta lakes are:

    1. The physical and chemical conditions within a lake and tolerances of different species to those conditions
    2. The abilities of different species to disperse into a lake.

    Ecology of delta lakes

    The biodiversity of delta lakes can differ greatly, not only between delta lakes but also within a single lake. Two key factors that determine the biodiversity in delta lakes are:

    1. The physical and chemical conditions within a lake and tolerances of different species to those conditions
    2. The abilities of different species to disperse into a lake.

    Lake zones of biological communities

    Generally four major ecological zones are identified in delta lakes (see figure on zones in standing water), providing different conditions for its biodiversity:

    A typical lake has distinct zones of biological communities linked to the physical structure of the lake.

    • The littoral zone is the near shore area where sunlight penetrates all the way to the sediment and allows aquatic plants (macrophytes) to grow. The littoral community is considered the most diverse and abundant biological community in lakes.
    • The euphotic zone of the lake is the layer from the surface down to the depth at which light levels become too low for photosynthesizers.
    • The limnetic zone is the open water area where light does not generally penetrate all the way to the bottom.
    • The benthic zone is the surface layer of the bottom, with sediments abundant with organisms. This upper layer may be mixed by the activity of the benthic organisms that live there, often to a depth of 2-5 cm in rich organic sediments.

    For an overview of these zones see: www.lakeacces.org.

    Lake food webs

    Aquatic plants and animals interact with each other through a series of interconnecting pathways called a food web. The various levels in the food web or chain are called trophic levels, each of which represents a different type of productivity. The interconnection between the trophic levels is often very complex and dependent on the local lake situation.

    In general, the foodchain in the aquatic environment starts with the primary producers, phytoplankton (predominantly algae) and macrophytes, that use sunlight, water and nutrients for photosynthesis. Phytoplankton is the primary food for many species of filter-feeding zooplankton. Zooplankton on its turn is eaten by planktivores, that include fish as well as a variety of aquatic insect larvae. The piscivores, fish-eating fish, are at the top of the aquatic food web. Extending the food web to the terrestrial environment,it becomes even more complex, with a multitude of relationships with birds, reptiles, amphibians, mammals, spiders and insects (see figure; from: http://www.waterencyclopedia.com/Hy-La/Lakes-Biological-Processes.html).

    Food webs of lakes can be fuelled by internal production, i.e. photosynthesis by plants, but also by external production, i.e. carbon and nutrient inputs from surrounding land. 

    In the text below, important elements and processes of the lake ecosystem are described.

    Macrophytes

    Macrophytes (large multicellular plants in lakes) play a very important role in the lake ecosystem. They add structure to the aquatic environment and support an abundance of life. In the littoral zone, many fish build nests in the vegetation and young fish find protection among the plants from predators. A multitude of aquatic insects (food for many fish) live on and feed among the plants. They also produce oxygen, which assists with overall lake functioning (from: www.waterencyclopedie.com).

    Macrophytes may be classified into several groups based on whether they are rooted (attached to substrate) or floating, and whether all parts remain submerged or some parts emerge out of the water (emergent).

    The absence of macrophytes may indicate water quality problems (Environmental Protection Agency) as a result of excessive turbidity, herbicides or salinization. This may result in a reduced population of (sport and forage) fish and waterfowl (Crowder and Painter, 1991). An overabundance of macrophytes as a result of high nutrient levels may also interfere with the ecosystem services that a lake can provide, e.g. recreational activities (swimming, fishing, boating) and aesthetic appeal.

    Microbial organisms

    Microbial organisms present in most lakes include unicellular and colonial algaerotifersprotozoabacteria and blue-green algae. Photosynthetic algae that float freely within the limnetic zone are referred to as phytoplankton. Dense blooms of phytoplankton may occur in lakes where nutrients are abundant, turning the lake turbid and green (eutrophic lakes).

    Invertebrates

    The invertebrate fauna of lakes mainly consists of crustaceansmolluscsoligochaete worms and adults, larvae or nymphs of insects. The tiny animals suspended in the water column are called zooplankton . Like phytoplankton, these species have developed mechanisms that keep them from sinking to deeper waters, including drag-inducing body forms and the active flicking of appendages such as antennae or spines. Remaining in the water column may have its advantages in terms of feeding, but this zone’s lack of refuge leaves zooplankton vulnerable to predation.

    The invertebrates that inhabit the benthic zone are numerically dominated by small species and are species rich compared to the zooplankton of the open water. They include crustaceans (e.g. crabs, crayfish, and shrimp), molluscs (e.g. clams and snails) and numerous types of insects. These organisms are mostly found in the vegetation of the littoral and euphotic zone, where the richest resources, highly oxygenated water, and warmest portion of the ecosystem are found. The structurally diverse macrophyte beds are important sites for the accumulation of organic matter, and provide an ideal habitat. The sediments and plants also offer a great deal of protection from predatory fish.

    Vertebrates

    A variety of vertebrate animals live in and around lakes. Species composition is very much dependent on the local situation.

    Fish are a notable species group in lakes, and represent an important part of the ecosystem services that delta lakes deliver. Fish species have specific physiological tolerances and preferences in temperature, dissolved oxygen concentrations, spawning needs. Because fish are highly mobile, they are able to deal with unsuitable abiotic factors in one zone by simply moving to another.

    Other vertebrate taxa of delta lakes include amphibians (e.g. salamanders and frogs), reptiles (e.g. snakes, turtles, and alligators), and a large number of waterfowl species. Most of these vertebrates spend part of their time in terrestrial habitats and thus are not directly affected by abiotic factors in the lake or pond. However, food shortage in the aquatic environment can severely affect waterfowl, for instance, which are heavily dependent on the food source that delta waters normally provide. 

    Eutrophication

    Enrichment of lakes with nutrients can cause algal blooms. This pollution is usually originating from agriculture, industry and urban centres. When nutrients accumulate, a lake ecosystem can quickly shift from an oligotrophic state (low nutrient levels, low productivity, clear water) or mesotrophic state (intermediate levels of nutrients, productivity and water clarity) to a eutrophic state (high nutrient levels, high primary production, low water clarity). Reduction of nutrient inflow (external loading) tends to be swiftly compensated by ‘internal loading’; the release of phosphorus stored in the bedsediments by wave and wind forces and foraging fish species. This is one of the reasons why bringing eutrophic and turbid lakes back to an oligotrophic or mesotrophic state is quite difficult and time-consuming. Ecological feedback mechanisms in lakes can be another reason why it is difficult to turn a eutrophic and turbid lake into an oligotrophic or mesotrophic and clear one.

    Alternative stable states

    Shallow lakes can have two alternative equilibrium states: a vegetation-dominated clear state and a turbid non-vegetated state. These equilibrium states are correlated with the nutrient levels in the lake. However, when a lake is in one equilibrium state, it does not easily flip to the other (see figure on critical turbidity of shallow lakes). This resilience is the result of feedback loops in the ecosystem.

    When nutrient levels increase, the density of algae increases and the water becomes more turbid. When a critical turbidity is exceeded, macrophytes will entirely disappear, as they do not receive light anymore (Scheffer et al., 2002). In turbid water, the number of piscivorous fish will decline, as these hunters need the submerge vegetation to hide in and need clear sight to see their prey. If the piscivore population is low, the number of planktivores fish will increase, resulting in a depletion of their principal food source, the zooplankton population. Less zooplankton eat less algae, resulting in higher algae densities. Also benthivorous fish will profit, as they forage by touch and are not hindered by the turbidity of the water. When foraging they stir up the soil. This combined with the absence of macrophytes will increase the turbidity of the water also by floating sediment and keep the lake in a turbid state.

    In a turbid lake, there is a relatively small bird community of piscivores and omnivores. Also, cyanobacteria often dominate the phytoplankton vegetation if the lake is in a turbid state. In the clear vegetated state the fish community is more diverse, and large numbers of herbivorous and omnivorous waterfowl visit the lake (Scheffer et al. 2002). A turbid lake delivers far less ecosystem services than a clear lake can. See here for more information. .

    Physical drivers

    The main physical processes in delta lakes are stratification, sedimentation and resuspension and wind-induced waves and currents.

    Stratification

    Thermal stratification is specific for the deeper delta lakes. It is caused by temperature differences within the water body. As the water heats up during the warmer summer time, a temperature gradient (thermocline) may develop between warmer surface waters and cooler deep waters. This thermocline acts as a barrier to vertical movements within the water body. The top layer (epilimnion) may become nutrient-poor as aquatic organisms use all available supplies and cannot access those below. The bottom layer (the hypolimnion) may become depleted of oxygen (hypoxic) because of its isolation and may even become anoxic, producing hydrogen sulphide. The thermocline usually breaks down in winter or under strong winds, allowing vertical mixing: the movement of nutrients upwards and oxygen downwards triggers a period of renewed growth.

    Sedimentation and resuspension

    In many lakes, inorganic sediment particles, but also algal cells, go through a rapid cycle of sedimentation and resuspension. Resuspension is often caused by turbulence as a consequence of wave action but also fish searching for food in the bottom can stir up considerable amounts of sediments (see figure on turbulence). Whether or not wave action leads to resuspension of particles depends on the shear velocity and on the properties of the sediment.

    Wind, waves and currents

    Wind is generally the main cause of waves in lakes. The two main determinants of wave heights are the strength of the wind (speed and duration) and the length of the lake on which the wind acts; the fetch. The longer the fetch, the higher the waves. Waves generate a horizontal water movement along the sediment surface which causes the resuspension of sediment into the water. Wave action, also called stirring, causes erosion of the shoreline in lakes and reservoirs. The severity of erosion of the shores depends on the geometry and materials that make up the shoreline.

    Other effects of wind acting on a lake are circulation currents and a water surface gradient. Wind sets down the water surface at the upwind side and sets it up at the downwind side. This can give rise to substantial water level differences and to a significant reduction of the wave-attenuating effect of wetlands, for instance. This determines the design conditions for lake-bordering flood defences.

    As the wind force acts at the surface, it will drive a water circulation in the vertical plane. Moreover, the force is more effective in shallower water, which means that horizontal circulation currents will arise if the lake has deeper and shallower parts. Together with the wave-induced water motion, these currents contribute to the mixing of the lake.

    Transitions

    Many delta lakes once were lagoons with an open connection to the sea. If closed off artificially, lagoons will go into a transition and cause specific management problems and challenges. Specific problems are:

    • A gradual decrease in salinity can create intermediate conditions that offer opportunities to noxious algae species, notably blue green algae. This may be a temporal state, but in some systems problematic conditions may prevail for decades. Management may focus on reinstating minimum salinity levels or increased flushing and reduced retention times.
    • Clay sediments can lose their aggregate stability because internal chemical cohesion is reduced as salinity decreases. As a consequence the lake bottom sediment is especially prone to suspension. Over time an unconsolidated mud layer develops that, decades after the closure, suffocates all benthic communities in the lake, leading to the reduction in food sources for birds and a reduction in fish communities.
    • Bottom sediments can accumulate phosphorus leading to enhanced internal P-loading that can be a major driving force for algae growth. The build-up of phosphorus can be gradual and water quality problems may become manifest only decades after closure. Problems can be severe to local fisheries, recreation and water supply. Management may opt for stringent emission control, increased flushing or even sediment management strategies. Also partially reopening of the closure dam is sometimes considered a management option.
    • Loss of tidal activity often leads to the concentration of wave energy in a narrow zone resulting in erosion of former tidal flats and the need for costly shore protection measures.
    • Loss of tidal activity may also lead to static and anoxic groundwater in riparian lands. Especially in lowland this process may affect large areas. Anoxic groundwater may lead to the die-off of root systems of trees and the geochemical release of toxic elements.

    Governance processes

    A characteristic of many delta lakes throughout the world is the fragmentation of management and administration. The governance of a lake and its coastal zones seldom falls within the competence of one organisation, and even in such cases management needs to handle competing claims and different perspectives on planning and decision making. Consequently every new initiative is target to  a large number of  organisations who want to influence planning and management decisions. Herewith, the decision making process becomes in a complicated interplay of parties whereby everyone and no-one feels responsible.

    In the face of fragmentation of management and administration, an integrated approach in planning and decision making is more appropriate in delta lakes than a sectoral one.

    For more information on governance processes see Governance.

    Ecosystem services

     

    Ecosystems provide all sorts of benefits - like goods or services - for mankind; these benefits are known as ecosystem services. Generally these services are divided into four categories (United Nations Millennium Ecosystem assessment):

    • Provision, such as the production of food and water
    • Regulation, such as soil retention
    • Cultural, such as recreational benefits and
    • Support, such as nutrient cycles. 

    For further reading on ecosystem services see here (TEEB).

    Provision

    • Freshwater supply for domestic, agricultural and industrial use. The IJsselmeer, for instance, is one of the largest freshwater reservoirs in Europe, providing 30% of the Netherlands with irrigation water during dry summers, water to flush the land to prevent salinization of soils and drinking water for one million people.
    • Protection of the hinterland against incoming storm surges by barriers and constructions in Delta lakes.
    • Fish production - fisheries are an important sector on e.g. lake IJsselmeer, where European Eel is an economically important species.
    • Opportunities for tourism --this is also often an important economic sector.
    • Supply of construction materials (mainly sand).

    Regulation

    • Safety against flooding of inland areas by the storage capacity of delta lakes for river or precipitation water.
    • Water storage of surplus water in winter/ the rain season, to be used in summer / the dry season.
    • Prevention of the discharge of sediment from the shores into the lake during flood events by the stabilizing effect of the natural riparian vegetation.
    • Water purification and pollution control through absorption, filtering and dilution of nutrients, pollutants and other wastes.
    • disease control by preventing the expansion of bacteria and microbes that possibly affect people.

    Cultural

    • Possibilities for recreational activities like sunbathing, swimming, fishing, bird watching, canoeing and yachting. A large part of the human population lives and works in cities near delta lakes, so this ecosystem service is of value for a lot of people.
    • Spiritual inspiration attributed to a certain lake.
    • A feeling of serenity and space.
    • Landscape aesthetics.
    • Cultural heritage and identity.

    Support

    • Nutrient cycling.
    • Partly due to spatial differences in vegetation, delta lakes provide wide diversity of habitat to invertebrates and (juvenile) fish.
    • Water cycling by storing, regulating and recharging surface and sub-surface waters.
    • Many shallow foreshores offer nursery habitats for e.g. fish and oysters.
    • Provision of nesting, resting and foraging habitat for waterfowl and migrating birds along dikes, dams, on berms/islands, flats.
    • Habitat for freshwater species.
    • The lake provides large amounts of food for international populations of fish- and mussel eating water fowls. The large dimension and relatively low depth of the lakes are appealing and some delta lakes (e.g. Ijsselmeer) are on the route of migrating birds or function as staging areas.
    • The natural, gentle slope of the shores result in large areas of shallow water that offers favorable conditions for aquatic and riparian plants to flourish. 

    Building with Nature

    A 'Building with Nature' approach aims to use ecosystem services of delta lakes for infrastructure development and management to the benefit of riparian societies, while at the same time creating new opportunities for the lake ecosystem. It tries to find a balance between human use of delta lakes and maintaining the integrity of ecosystem functioning. BwN opportunities for delta lakes are explored in the next paragraph.

    BwN opportunities

    Delta lakes offer many opportunities for building with nature, and building with nature has a lot to offer to delta lakes. In the case of lakes most BwN measures are multifunctional and integrated solutions for a variety of objectives. Ecological recovery, for instance, can go hand in hand with socio-economic development and flood safety can be realised with benefits for nature, water quality and recreational activities, sometimes even at lower costs.

    Below some of these opportunities are presented, categorised in four themes: natural flood defences, wave-driven sand nourishment, spatial solutions and recreational development. The main focus of the examples given is on the necessary improvement of flood defences and on recreational development.

    Natural flood defences

    To protect the low-lying hinterland from flooding, many delta lakes require flood defences. A BwN opportunity is to engineer these defences in a more nature-oriented way. Three different types of ‘natural’ flood defences have been designed that are both cost effective and beneficial to nature and recreation (Fiselier, 2011):

    1. Soft water defences
    2. Hybrid soft water defences
    3. Hybrid hard water defences
      3.1 Overtopping dike (overslagdijk)
      3.2 Constructive solutions

    Even though all measures have similar goals, they are all based on different principles.

    Soft water defences

    When water defences need to be improved, soft measures can be taken, rather than broadening or heightening dikes. The function of the dike as main safety provider is not changed, but is complemented with a soft engineering measure.

    A soft measure that increases the flood safety level in the hinterland is the creation of gently sloping shallow foreshores, as they reduce the wave attack on the dike. These foreshores can sustain a variety of vegetation and associated wildlife. This type of flood defence improves the functioning of the ecosystem and provides a variety of recreation opportunities. It delivers all type of ecosystem services: provision, regulation, support and cultural services. Moreover, these types of measures are often more cost effective than ‘normal’ safety improvements like dike strengthening.

    The figure shows different types of soft water defences. The coloured boxes indicate the benefits of these defences for safety and the emerging values for nature and recreation.

    Hybrid soft water defences

    Hybrid Soft water defences are founded on similar principles as soft water defences. Also in this case, the dike as main safety provider remains. By varying the foreshore extent and depth, its strength and stability (piping!) can be increased in a natural way. Also this measure improves the conditions for nature and for recreation. Again, the costs of ‘normal’ safety improvements are often much higher. An example of a hybrid soft water defence system is the wave reducing eco dike, to be constructed near the city of Gorinchem (NL).

    The figure shows different types of hybrid soft water defences. The coloured boxes indicate the benefits of these defences for safety and the emerging values for nature and recreation.

    Another opportunity is the creation of so-called ‘back shores’ which are shallow wetlands on the landward side of the shore. These back shores increase the safety of the inland area and offer good conditions for nature.

    When dikes are not strong enough and are vulnerable to wave overtopping, covering the construction with clay can make it more resilient. If this clay can be derived from the area behind the dike, this will leave excavation pits which are good opportunities for the development of new nature areas (Groot et al., 2012).

    Hybrid hard water defences

    Overtopping dike (overslagdijk)

    All dikes can handle a certain level of overtopping in case of high waters. When a certain threshold is surpassed the dike integrity can be compromised, with catastrophic consequences. If heightening dikes is unfavourable (e.g. too costly or because of aesthetic values) an overtopping dike is an option. This type of dike can better deal with overtopping. So, even though water can spill over the dike, an actual breach might be prevented.

    Hybrid hard flood defences: constructive solutions

    All hybrid hard flood defences aim at absorbing as much energy as possible before waves reach the actual dikes. This can be achieved by several measures: poles, floating marshes, reefs or shallow foreshores. The benefits of these measures for safety and for nature and recreation vary. Not all types offer opportunities for recreation or nature development.

    The figure shows different types of hybrid hard water defences. The coloured boxes indicate their benefits for safety and the ensuing values for nature and recreation.

    Wave driven sand nourishment

    Many BwN measures - including many of the ones described above – make use of sand nourishments at strategic places. In the case of shallow lake shores, this can be done by directly placing the sand in the desired position, thus burying the substrate. But it can also be done indirectly, placing the sand on the shore face and using the water motion to transport the sand to the desired location. This approach has several effects:

    • New (temporal) habitats are created. The nourishments create sand banks where birds can forage, breed and rest and pioneer vegetation can settle.
    • Gradual accretion of the coast. If functioning as expected, an indirect sand nourishment results in ‘natural’ sedimentation of the coastal zone. Thus vegetation can survive and the shore has the potential to follow a gradual rise of the lake levels. Next to preserving flood safety by maintaining the shallow foreshore, other ecosystem services can be strengthened. The shores can act as a nesting and foraging habitat for waterfowl and vegetation can stabilize the soil, thereby reducing erosion. Also, the shores can be used for recreation.

    Spatial solutions - connections with land use

    Following recognition of climate uncertainties new approaches to flood security are emerging. One of these is called ‘multi-layered safety (MLS). MLS is different from the current policy concerning flood protection, which is based on chance of exceedance of a dike, barrier or other flood protection work. MLS focuses instead on chance of flooding and incorporates flood risk and the potential consequences of a flood in the hinterland of the dike (Broekhans, Coreljé & Van Ast, 2010). This three step approach was developed after evaluations by Dutch experts of the implications of the Katrina disaster in New Orleans for the Dutch flood defence system. First step is prevention of floods through sound infrastructures like dikes. The second is anticipation on failure by design of a sustainable spatial planning, for instance vulnerable functions like hospitals, elderly homes and power plants are situated on locations with low vulnerability. The third step is the organisation of disaster management, for example by preparing evacuation plans and by exercising (van den Brink et al. 2011). These three steps existed already individually, but in the multi-layered approach the steps are treated as interdependent elements of one flood protection chain. The approach is now being tested in pilot areas in the Netherlands. An important implication is that discussions on spatial planning and on disaster management involve actors in the pilot areas, who do not belong to the ‘traditional’ flood security expert community (Ludwig et al., 2012).

    Recreational development

    Delta lakes are attractive for recreation and many people travel long distances for the opportunity to recreate in and around the lakes. Harbours and beaches, marshes, shores and the open water offer many different sights and a high landscape variety. The area constantly changes as a result of the dynamics in the water and the gentle water – land gradient. Although the recreation areas around delta lakes often are numerous, the atmosphere remains still quiet and peaceful as a result of the large size of the lakes.

    Traditionally, large construction works for recreational purposes are made by creating hard, concrete constructions, which are seldom improving the quality of the area for recreation. With the BwN approach, the construction works can be carried out in a way that they add to the recreational quality of the area. An example is the use of sand surplus of sand mining and dredging activities for creating areas around and on engineered structures where bio-engineers can settle and thrive.

    Case examples

    The Delta Lake case within Building with Nature is the 'Markermeer- IJsselmeer' case. This section starts with an introduction of the area and its current challenges. In addition EcoShape is involved in the pilot “Friesche IJsselmeerkust” in which sand engine experiments are carried out on three locations (Hindeloopen, Workum and Oude Mirdum).

    Case Markermeer- IJsselmeer

    The Markermeer- IJsselmeer lake area is one of the largest fresh water reservoirs in Europe. The area consists of smaller border lakes of the polders of Flevoland province (Randmeren) and three major lakes: the IJmeer, the Markermeer and the IJsselmeer. The Markermeer - IJsselmeer system functions as a freshwater reservoir for the Netherlands. During dry summers, the IJsselmeer provides 30% of the Netherlands with irrigation water and drinking water for 1 million people. Moreover, it acts as a flood water buffer for the surrounding land.

    History

    Before the enclosing dike (‘Afsluitdijk’) was completed in 1932, the Markermeer and IJsselmeer were part of a brackish inland sea called the 'Zuyderzee’ (see historic map). The dike eliminated the tidal dynamics and in- and outflow of salt water in the lake area. Over time, marine sediments -rich in nutrients- had settled on the lakebed. Former salt marshes nowadays remain just a little above mean lake level. Via a number of mechanisms, the sudden change in water dynamics and the gradual change from brackish to fresh water have increased turbidity in the southwestern part of the lake. The Markermeer was artificially created in 1976, when the ‘Houtribdijk’ was built between the cities of Lelystad and Enkhuizen (see figure of current topography of Markermeer and IJsselmeer). This has aggravated the turbidity problem.

    Challenges

    Turbidity

    The Markermeer suffers from high turbidity caused by wind-induced resuspension of fluffy bed sediment (see aerial photograph showing the mud content of the Markermeer). This sediment contains high nutrient levels and its resuspension may lead to eutrophication of the lake. If the high turbidity and eutrophication continue, they may have severe effects on the lake’s fisheries, aesthetic values and recreational function and cause economic damage. The current more or less stable turbid state is therefore to be pushed towards another, more clear stable state. Changing a system from one stable state to another requires a thorough understanding of the system dynamics, as well as significant efforts. Therefore, authorities involved are formulating a substantial investment programme.

    Natura 2000

    The Markermeer- IJsselmeer area is a designated Natura 2000 area and an important habitat for many aquatic species and birds. The shallow parts and the former tidal flats are habitat for protected Natura 2000 species and crucial foraging and resting habitat for migratory birds. Yet, the success of the N2000 species in the Markermeer – IJsselmeer is declining. The graph in the figure on the side shows a simplified representation of the ‘autonomous’ declining trend of N2000 species in the IJsselmeer (red line). In order to compensate the negative impacts of human activities, a surplus of ecological quality would be needed (green line).

    Fragmented governance

    Governance in the Markermeer- IJsselmeer area is fragmented. While the lake water itself is managed by the Directorate-General for Public Works and Water Management, riparian municipalities and provinces each have land use strategies and nature and environmental regulation. Waterboards are responsible for inland water quality and the flood defence system. All in all, policy making in the area may involve more than 50 governmental institutions. Moreover, several NGO’s and action groups try to influence decision makers, while a number of laws and legislation apply in the area (e.g. land use strategy regulations, Water Framework Directive, Natura 2000, Dutch Water Law).

    Current developments

    At the moment, two major issues are calling for administrative and scientific attention in the Markermeer- IJsselmeer area. The first is the future strategy for the Markermeer (Stuurgroep TMIJ, 2009). Lake management must comply with environmental standards, which is currently not the case. At the same time, the lake is subject to all kinds of new plans (e.g. creating artificial islands and new housing areas in the lake).

    The second issue is the climate change adaptation plan for the IJsselmeer. The Dutch Delta Committee (2008) advised the Netherlands government on a long-term adaptation strategy for Dutch water systems. One of the recommendations of the Committee was to anticipate a maximum sea level rise of 1.5 m by the year 2100, which would have severe impacts on the lake level management in the IJsselmeer. The committee’s advice led to a Delta Act and a Delta Program to prepare for the envisaged environmental changes. The subprogram ‘IJsselmeergebied’ of the Delta Program has started a multi- stakeholder policy development process in which possible lake management strategies are being investigated.

    Pilot Friesche IJsselmeerkust

    In the case Markermeer-IJsselmeer a pilot on the Friesche IJsselmeerkust has been carried out to experiment with the ‘soft sand engine’ and to learn about its effects on the marshes along the Friesche IJsselmeerkust.

    In 2009 the planning of three so-called ‘sand engine experiments’ in front of the Frisian IJsselmeer coast started. These sand engines are potential adaptation measures for a coast under the influence of rising water levels due to climate change. The implementation is governed by a coalition of regional and national actors, led by It Fryske Gea. The objective of the experiment is to test the functioning and effectiveness of different lay-outs and designs of sand engines in combination with bioengineers. In order to do so, sand nourishments are executed in order to stimulate broad gradual foreshores. Pioneer vegetation (bioengineers) will then emerge which diminish erosion and thereby offering opportunities for more robust nature. Moreover, when sand and mud flats are preserved, vulnerability of the nature areas outside the dikes by flooding is reduced. At the same time, this newly created nature area functions as wave inhibitor. Thereby this integrated measure also serves as coastal protection function for the future by creating a natural buffer. Besides, a coast line that is robust and diverse in the same time gains higher enchantment for recreational activities.

    Historic cases

    Next to the pilots, four historic cases in the Markermeer-IJsselmeer area have been assessed as these cases can be seen as predecessors of the pilots.

    Workummerbuitenwaard

    In September 1992, a sand bar was constructed along the Workummerbuitenwaard at 1m below mean sea level. The sand bar- with a length of 2 km and a width of 120 m- was located 450 meters from the coast and not protected by any artificial structure. The bar was supposed to move eastwards, yielding coastal sedimentation and expansion of the marshes along the shore. The conclusion found is that sand nourishments in a highly dynamic environment do not automatically lead to sedimentation in shallow waters and sedimentation along the coast. Most of the sediment is being transported on a local scale towards deeper parts of the water. Sand nourishments in the case of the Workummerbuitenwaard did not result in growth of the shoreline, nor in heightening of terrestrial areas.

    Mirnserklif

    Mirnserklif is located along the Frisian IJsselmeer coast, east of the city of Stavoren. It is connected to the nature area ‘Mokkebank’ which is managed by the nature protection association ‘It Fryske Gea’.In 1993, four undefended (e.g. not protected by any artificial structure) sand bars were constructed. In total, 120,000 m3 of sand was replaced. The height of the sand bars varied from 0,20m +NAP to 0,20m --NAP. The main goal of the project was to create foraging, resting and nesting habitat for reed-and marsh-dependent birds by extension of the marshland. The experiment at the Mirnserklif was perceived as quite successful; this can amongst others be attributed to the location. Mirnserklif is located in a lee area close to the mainland which is important for the local transport and sedimentation in between the (former) islands and for the development of the coast and reed land.

    Veluwerandmeren

    The Veluwerandmeren were formed after the creation of the eastern part of the polder Flevoland. The Veluwerandmeren include the lakes Drontermeer, Veluwemeer, Wolderwijd and Nuldernauw. It is a diverse but ecologically fragile area with a variety of functions. The Veluwerandmeren are a wetland of international importance with a high diversity in waterfowl and aquatic plants. Other functions are shipping, swimming, sport-and professional fishing, drinking water provision and reed cultivation. The project VeluweRandmeren (in Dutch: Integrale Inrichting VeluweRandmeren or IIVR) was initiated in 1996 to integrate different legislation and plans for the area and is a cooperation between 19 governmental agencies. Together with stakeholder groups and inhabitants they (re)designed the area between the Nijkerkersluis and the Roggebotsluis close to the city of Kampen. The ultimate goal is to implement a package of integrated measures for the Veluwerandmeren to improve the spatial quality and to restore the balance between nature and recreation. The suppletions appear to prevent and stop erosion of beaches and dunes and are regarded as being successful.

    It Soal

    The project It Soal is executed along the Frisian IJsselmeer coast at the level of the Workumerbuitenwaard between 1995 and 1997. It consists of a constructed longitudinal groyne and two sandbars. The main purpose was to create rest,- moult,- and foraging habitat for wading birds. The dike and sandbars also functioned as zoning structures to separate nature and recreational areas. The project is successful in reaching its objectives. The groynes contributed to retain the sediment as well as to the zonation of nature and recreation.

    Lessons learned

    The lessons learned are specifically derived from the pilots and historic cases under the Markermeer-IJsselmeer case.

    Physical processes

    • Sand nourishments at locations with a low level of hydro-dynamics can create new shallow zones and habitats by dispersion of the sand.
    • Sand nourishments at locations with a more dynamic water motion may completely vanish from the shore.
    • Local system behaviour is subordinate to larger-scale system processes such as currents, water level set-up and pollution. Interactions between higher and lower level system behaviour need to be understood in order to enable sensible planning and design.
    • Forecasting of sediment transport and morphological processes in low-dynamic areas is complex. Specific hydro-morphological knowledge and tools are needed to understand them. Monitoring and data analysis are therefore important whenever an experiment is carried out.
    • Wind offers additional dynamics to the exposed shallow shores along the coast. It may change the soil profile and the balance between erosion and accretion of sand. These dynamics create favourable conditions for a high value nature development.
    • Wind lowers the water level at the upwind side of the lake and sets the water level up at the downwind side. This may yield substantial water level differences in the lake and result in a significant reduction of the wave-attenuating effect of wetlands on the downwind side. These wind effects should be taken into account in the design requirements for lake-bordering flood defences. 

    Ecological processes

    • Shore nourishments are maintenance measures. Initially they contribute to creating new terrestrial habitat with pioneer vegetation. In the longer run, they tend to spread alongshore and over the shoreface, thus contributing to sedimentation in the coastal zone on local and regional scales and offering possibilities for water-, marsh- and shoreline vegetation to develop.
    • A slow decrease in salinity can create favorable conditions for toxic algae species, notably blue green algae. This may be temporary, but in some situations these conditions may prevail for decades. Management options are to set minimum salinity levels or to increase the flushing velocity, thus reducing the detention time of the water.
    • As salinity decreases, clay particles can lose their cohesion as a result of a chemical process. As a consequence, the lake bottom sediment is prone to suspension and over time an unconsolidated mud layer may develop at the bottom of the lake. This mud suffocates benthic communities, leading to the reduction in food availability for many species.
    • Bottom sediments can accumulate phosphorus elements. This mays to an enhanced internal P-load that can be a major driving force for algae growth in the lake. The build-up of phosphorus in the sediment is gradual and can cause water quality problems even decades after the separation of the delta lake from the sea. The decrease in water quality can cause severe problems for fisheries,  recreation and water supply. Management options are a stringent control of emission, increased flushing or even sediment management. Also inlet of seawater by partially opening dams is sometimes considered an effective option.

    Governance processes

    • In the face of fragmentation of management and administration, an integrated approach in planning and decision making appeared to be more successful in delta lakes than a sectoral one, because:
      • urgent short term objectives in spatial planning for certain land use functions can be connected with longer-term  strategies e.g. for safety against flooding and fresh water supply;
      • knowledge of a diverse group of stakeholders (e.g. local lake users, research scientists, community members with traditional knowledge, government representatives) becomes available in the project development process, which leads to more and better underpinned options and better supported decisions;
      • it can lead to multifunctional projects and  win-win situations. For example, the construction of shallow foreshores in the IIsselmeer (the Netherlands) was as a safety measure that contributed to the ecosystem functioning of the lake, increased the spatial quality of the area and promoted the multifunctional usage of the area (Groot et al., 2012).
    • Well-considered framing of the tasks and a clear project mission is of crucial importance. A scope defined too narrow misses out potential opportunities. Therefore, integration needs to be sought in the process of decision making in order to find win-win conditions.
    • Be clear about the objectives and find commitment of stakeholders on these. For instance, in the IJsselmeer area, the fact that all parties concerned expressed the objective to create conditions for fish migration gave the project an impulse. 
    • Pay attention to the consultation of authorities from the beginning of the planning and design phase. Timely start and manage formal procedures. In many stakeholder settings, authorisation requests and permit procedures are rigid and time consuming, with unexpected turns and developments.
    • Start in the initiation phase with a small creative project team with a wide range of expertise and a mandate to make its own decisions. This enables them to quickly respond to unexpected developments.
    • Multi-stakeholder involvement leads to a longer planning and implementation period, but it usually saves time during permit acquisition procedures and execution of works.
    • Carefully consider stakeholders’ interests and translate those interests in multi-functional designs.
    • Decision making, legal procedures and networking are part of the BwN design and implementation process. When dealing with conflicting interests three purposefully implemented strategies proved helpful:
      • Beware of closing design discussion too early by presenting too unambiguous pictures, clear definitions, representations and technical designs. By keeping options open and somewhat vague, potential partners have the opportunity to translate their own interests into the plans, thereby avoiding early clashes on end results.
      • Produce a short movie with decision makers expressing the importance of a BwN approach to the project. It shows the support of high-ranking officials for the experiments provides informal legitimation and facilitates negotiations.
      • Arrange political and high level sponsorship by inviting officials to visit the project area.
    • Communicate at multiple levels. Involve authorities at regional and sub-local levels as well as local stakeholders. Especially local stakeholders tend to be overlooked in (often complex) discussions and decision making processes at higher scale levels. Create a ‘ Community of practice ’.
    • A joint problem or opportunity, such as the BwN experiments, stimulates cooperation between stakeholders. A covenant in which rules of the game are made explicit, including funding responsibilities, favour an effective cooperation between stakeholders. Consider options for ‘ Financing ’. 

    References

    Literature

    Broekhans, B., A.F., Correlje, J.A. &, Van Ast, 2010. Allemaal op de bok: Naar de implementatie van een nieuw waterveiligheidsbeleid. In: Kijk op waterveiligheid (pp. 122-149) door H. Van der Most., S. De Wit, , B.Broekhans,& W. Roos, (Eds.), Delft: Eburon Delft.

    Crowder, A. & D.S. Painter, 1991. Submerged macrophytes in L. Ontario: current knowledge, importance, threats to stability and needed studies. Can. J. Fish. Aquat. Sci.88: pp1530-1545.

    Fiselier ed., 2011. Perspectief Natuurlijke Keringen: Een eerste verkenning ten behoeve van het Deltaprogramma.Sichting Ecoshape. Dordrecht. Netherlands.

    Folke C., T. Hahn P. Olsson & J. Norberg, 2005. Adaptive governance of social-ecological systems. Annual Review of Environment and Resources30: pp 441-473

    Groot, A., G.Lenselink, , E. van Slobbe, G. van Meurs, , R. Noordhuis, A. Wiersma,. M.Bos, I. Pasmans,. P. Dnakers, & T. Wilms, 2012. Natuurlijk Ijsselmeer: ecodynamische visie Ijsselmeer 2100. Building with Nature. Ecoshape. Dordrecht. Netherlands.

    Gulati, R.D, L. M. Dionisio Pires, E.Van Donk, 2008. Lake restoration studies: Failures, bottlenecks and prospects of new ecotechnological measures. Limnologica - Ecology and Management of Inland Waters 38 (3–4)

    Gunderson L.H. & C.S.Holling, 2002. Panarchy: understanding transformations in human and natural systems. Washington D.C., Island Press.

    Ludwig, F., E. van Slobbe, & W. Cofino, 2012. Climate Change Adaptation and IWRM in the water sector. Submitted to the journal of Hydrology.

    Scheffer M., F. Westley, W. Brock & M.Holmgren, 2002. Dynamic interaction of societies and ecosystems: linking theories from ecology, economy and society. pp 195-235 in: L. H. Gunderson & C. S. Holling, (eds). Panarchy: understanding transformation in human and natural systems. Island Press, Washington, D.C., USA.

    Smit M. & K. Lulofs, 2011. Monitor Building with Nature in the IJsselmeer Area. Case Studies: Bypass Kampen and Building with Nature experiments MIJ case. Ecoshape. Dordrecht. LINK

    Stuurgroep Toekomstagenda Markermeer en IJmeer, 2009. Toekomstbeeld Markermeer – IJmeer. Natuurlijk ontwikkelen.

    www.markermeerijmeer.nl/homedownloads/70737.aspx?t=Ontwikkelingsperspectief%20(2008)%20en%20Achtergronddocumenten. Dec. 2011

    Van den Brink, M., C. Termeer, , S. Meijerink, 2011. Are Dutch water safety institutions prepared for climate change? Journal of Water and Climate Change 2: pp. 272-287.

    Van Eerden, M., H. Bos & L. Van Hulst (eds.), 2007. In the mirror of a lake : Peipsi and IJsselmeer for mutual references. Ministry of Transport, Public Works and Water Management, Rijkswaterstaat, Centre for Water Management, Regional Directorate IJsselmeergebied.

    Internet

    Images

    • Taiu, China
    • The Building with nature case area 'IJsselmeer'(the Netherlands)
    • Lake Peipsi in Estonia and Russia
    • Four major zones in standing waters
    • Food chain of the aquatic zone
    • Submerged plants play in important role in the food web and lake turbidity (from: Gulati et al., 2008)
    • Approach of multi-layered safety
    • Foodweb of a lake
    • Shallow lake in vegetation dominated clear state and in turbid pytoplankton dominated state
    • Recreation at IJsselmeer
    • Cutting reeds in the shores of Lake Taihu, Cina
    • Soft Water defences
    • Hybrid Soft Water defences
    • Hybrid Hard Water defences
    • Historic map of former estuary
    • Current topography of the Markermeer and IJsselmeer
    • Aerial phtopraph showing the high silt contant of the Markermeer water
    • Simplified representation of the autonomous declining trend of numeber of species in Lake IJsselmeer

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