View source for Ecological restoration of estuaries in North Western Europe


This article is largely based on Ducrotoy, J-P. 2010. Ecological restoration of tidal estuaries in North Western
Europe: an adaptive strategy to multi-scale changes. Plankton Benthos Res 5(Suppl.): 174–184.

== Introduction ==

[[Estuaries]] are open systems and are essential interfaces between rivers and the coast. They constitute main transition zones or ecotones between land, the ocean and the atmosphere. In the [[North Sea]] and the English Channel (North-West Europe), the role of the [[tide]] is paramount, with a tidal range over 10 m in some areas. So, large macrotidal estuaries have developed there (the Elbe, the Weser, the Scheldt, the Humber, the Thames, the Seine,...). Geomorphology is essential to understand when comparing such estuaries. It is rapidly evolving because of natural processes (mainly hydrological, due to sea level rise and increasing tides). Estuaries are also greatly influenced by changes in the watersheds. The main factors affecting the hyporheic zone are the width and the depth of the river bed, the river flow and constructions (dams, embankments, polders...) by humans. Human activities, mainly through reclamation, have accelerated natural morphological processes and worsened the degradation of estuarine resources <ref name = "berkes">Berkes F, Hughes TP, Steneck RS, Wilson JA, Bellwood DR, Crona B, Folke C, Gunderson LH, Leslie HM, Norberg J, Nyström M, Olsson P, Osterblom H, Scheffer M, Worm B (2006) Ecology—Globalization, roving bandits, and marine resources. Science 311: 1557–1558.</ref>. In the estuaries presented here, the erection of dykes and the reclamation of land have dislocated the hydro-systems and limited access to estuarine animal and vegetal communities. Longitudinally, there has been an increase of tidal effects and salinity which have forced some estuarine species out of estuaries. The turbidity maximum also has a general tendency to move outwards. Transversally, dykes have broken connections between aquatic [[habitat|habitats]] and reduced the area and diversity of wet land, including intertidal flats and salt marshes. In all ecosystems, there has been a parallel decrease of fresh water tidal habitats for fish, birds, and the benthos on which they feed.
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[[Estuaries]] within Europe are managed to protect features designated under EU directives, notably their habitats and species in order to build upon their conservation objectives. This approach is no different from that adopted in other countries, for example the US [[Clean Water Act]]. Ecological [[Ecosystem restoration|restoration]] requires to build these into an iterative environmental management system which treats the environment as an entity to be managed as a whole <ref name="Eliot 2010">Elliott M. & Ducrotoy J.-P. (2010). Management plans for four North Sea estuaries : the Elbe, the Weser, the Humber and the Scheldt. ECSA Bulletin, 55: 15-22.</ref>. This is why, on the long-term, the main objective of estuarine habitat restoration in Europe is to enable the gradual re-establishment of ecological functions, leading to the (re)installation of typical estuarine communities. This can be accomplished through increasing fluxes of water circulating in the estuary and re-establishing connections between the various aquatic components of ecosystems. Adopting such objectives means considering each estuary as a whole including peri-estuarine areas such as the flood plain, associated marshes and land claimed by humans essentially over the last 150 years.
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== Ecological stability of estuaries ==

Despite radical changes in their morphology over a centenary and a half, North-West European estuaries are still productive [[Marine habitats and ecosystems|marine ecosystems]]. In all of them, [[Marine Biodiversity |biodiversity]] reflects their ecological value, not necessarily in terms of species richness, but in terms of diversity of habitats and biotopes <ref name="Ducrotoy 2010a">Ducrotoy JP (2010) La restauration écologique des estuaires. Lavoisier, Paris, pp. 196.</ref>. Biotopes constitute sub-units of ecosystems and are displayed as a mosaic in each [[estuary]] <ref name="Olenin2006">Olenin S, Ducrotoy JP (2006) The concept of biotope in marine ecology and coastal management. Mar Pollut Bull 53: 20–29.</ref> . They seem to be similar in all estuaries but what makes each estuary special is the physical, chemical and biological (biogeochemical) links between the biotopes. These interrelations depend upon hydrology, sediment transport, [[Nutrient conversion in the marine environment|nutrient transfer]] and biological cycles. Naturally, other variations between estuaries exist. The main structuring environmental factors appear to be [[salinity]], water movements and [[turbidity]]. They affect the heterogeneity (or structure) of each ecosystem, as well as their complexity (in terms of relations between structural attributes). 
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Despite radical changes inflicted on them, the estuaries presented in this paper stand out as specific and valuable socio-ecosystems. They consist in highly dynamical systems and the global change is increasing the speed of change. Even with the pressure exerted by human societies on their ecology, estuaries stand as assets to humans. Similar ecological functions are found in all of them, which provide valuable goods and services to human societies <ref name="Costanza1993">Costanza R, Kemp WM, Boynton WR (1993) Predictability, Scale, and Biodiversity in Coastal and Estuarine Ecosystems— Implications for Management.Ambio 22: 88–96.</ref>. Amongst those, biogeochemical cycling, in particular nutrients, water purification and mitigation of floods are much looked for. Tett ''et al''. (2007) <ref name="Tet2007">Tett P, Gowen R, Mills D, Fernandes T, Gilpin L, Huxham M, Kennington K, Read P, Service M, Wilkinson M Malcolm S (2007) Defining and detecting undesirable disturbance in the context of marine eutrophication. Mar Pollut Bull 55: 282–297.</ref> suggested that an ecosystem impacted by anthropogenic factors may, because of its resistance to disturbance, initially show little response to increasing pressure (figure 1). Pushed beyond a certain point, however, change becomes rapid, and may culminate in a radically altered state from which recovery would be slow (see also the article [[Resilience and resistance]]). An example would be the occurrence of extensive deep water anoxia, resulting in the widespread elimination of benthos and fish in the Scheldt and the Seine in the 1990s<ref>Billen, G., Garnier, J. and Rousseau, V. 2005. Nutrient fluxes and water quality in the drainage network of the Scheldt basin over the last 50 years. Hydrobiologia 540: 47-67</ref>.  A key operational need, when considering restoring any estuary, is to detect a trend towards such a widespread undesirable disturbance before the ecosystem has reached the limit of its resistance <ref name="Diaz 2008">Diaz, R.J. and R. Rosenberg. 2008. Spreading dead zones and consequences for marine ecosystems. Science 321: 926-928.</ref>. Case studies show however that ecosystems do not return to the same state after removal of a pressure, but to a different one. Re-estuarisation often implies re-creating damaged habitats from scratch <ref name="Ducrotory">Ducrotoy J.-P. (2011) Ecological restoration of tidal estuaries in North Western Europe: an adaptive strategy to multi-scale changes. Plankton Benthos Res 5(Suppl.): 4–14.</ref>.
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 {| width = "600" align ="center" style="text-align:center; font-size:85%"
|valign="top"| [[File:EcosystemHysteresis.jpg|600px]]
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|valign="top"|Figure 1: Hysteresis in ecosystem response to temporary disturbance. An ecosystem impacted by anthropogenic factors may, because of its resistance to disturbance, initially show little response to increasing pressure (adapted from [http://www.hull.ac.uk/iecs/ IECS]).
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=== The Humber ===
In the Humber, connectivity between the various aquatic components of the ecosystem has been shown to be the key to all restoration actions <ref name ="Cave 2003">Cave RR, Ledoux L, Turner K et al. (2003) The Humber catchment and its coastal area: from UK to European perspectives. The Science of The Total Environment 314–316: 31–52.</ref>. [[Pollution]] and [[eutrophication]] needed to be tackled <ref name="MazikElliot2000">Mazik K, Elliott M (2000) The effects of chemical pollution on the bioturbation potential of estuarine intertidal mudflats. Helgol Mar Res 54: 99–109.</ref><ref name="Mazik2004">Mazik K (2004) The influence of a petrochemical discharge on the bioturbation and erosion potential of an intertidal estuarine mudflat (Humber estuary, UK). Unpublished PhD thesis, University of Hull.</ref> while setting back the shore line was required in response to sea level rise. In order to test techniques for reconnection, a large scale experimental site was chosen in the 1990s for depolderisation and habitat (re)creation. In 2010, the Humber estuary was the site of three existing managed realignment sites (former agricultural land) with the primary role of direct compensation for habitat loss. A fourth site was being created as part of a flood defence scheme. Creation of a further five sites, with the primary aim of mudflat creation, is planned over the next 20 years <ref>Environment Agency (2009) Humber tides news: the Humber Strategy. Environmental monitoring report 2009, pp. 8.</ref>.<p>
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=== The Elbe===
In the Elbe, concern arose in the 1990s because of accumulation of sediments which limited access to Hamburg harbour <ref name="Plus2004">Plüß A (2004) Nichtlineare Wechselwirkung der Tide auf Änderungen des Meeresspiegels im Übergangsbereich Küste/ Ästuar am Beispiel der Elbe. In: Proc Klimaänderung Küstenschutz, pp. 129–138.</ref>. A restoration plan was launched based on a control of local sediments dynamics in order to improve navigability through the tidal areas (volumes, distribution, quality,...). This sediment management concept intends to relocate fresh, non-contaminated sediments in areas where there is less possibility for them to return to the place where they were dredged <ref>Fickert M, Strotmann T (2007). Hydrodynamische Entwicklung der Tideelbe. Coastline Reports Nr. 9: 59–68.</ref>. The opportunity was taken to improve environmental quality in association with engineering work realised to reverse negative geomorphological effects. Measures for restoring natural conditions along the river were taken, including conservation and development of shallow water areas, creation of alluvial forests, and salt marsh development in front of dikes. In the meanwhile, protected areas became attractions for tourists <ref>Bergemann M. (2006) The Elbe estuary. In: Seine-Aval special issue, north-Atlantic estuaries: problems and perspectives (edDauvin J-C), Rouen, pp. 43–46.</ref>. The re-creation of inter-tidal areas including salt marshes was initiated in order to increase floodable areas. It was aided by the installation of flood polders as buffers in case of [[storm surge]]. These restoration actions also provided flood risk protection in reducing storm surge water levels. Both recreational and commercial fishing will further benefit from the creation of shallow water zones. These are important spawning and hatching zones for fish and prey. An enhanced connection of tributaries also had a positive effect on the functioning of the estuarine ecosystem as migrating fish species could now reach their breeding areas with less effort. According to the [http://www.hamburg-port-authority.de Hamburg Port Authority], on the long run, the diversification of the system and the ecological improvement of the water and sediment quality very likely will increase the number of species <ref name="Ducker 2006">Dücker P, Glindemann H, Witt H-H, Thode K (2006) Concept for a sustainable development of the Tidal Elbe River as an artery of the metropolitan region Hamburg and beyond.</ref>. Application of scientific results led to interesting operational aspects when dealing with dredging of huge volumes of sediments. For instance, the use of models made their management more effective. 
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===The Scheldt===

Past management and unexpected changes have had a negative impact on the delivery of ecosystem services by estuaries and hence on the [[Resilience and resistance|resilience of ecosystems]] <ref name="Folke2002">Folke C, Carpenter S, Elmqvist T, Gunderson L, Holling CS, Walker B, Bengtsson J, Berkes F, Colding J, Danell K, Falkenmark M, Gordon L, Kasperson R, Kautsky N, Kinzig A, Levin S, Mäler KG, Moberg F, Ohlsson L, Olsson P, Ostrom E, Reid W, Rockström, Savenije H, Svedin U (2002) Resilience and sustainable development: Building adaptive capacity in a world of transformations. Ambio 31: 437–440.</ref><ref name=Gunderson>Gunderson L and Folke C (2005) Resilience—Now more than ever.EcolSoc 10: 22.</ref>. This resulted in growing socio-economic problems (e.g. inundations, eutrophication, siltation, ...) in the various instances considered. The carrying capacity and the assimilative capacity of ecosystems might be overrun and signs such as [[pollution]] show that their ecological functioning is affected <ref name="Arrow">Arrow K, Bolin B, Costanza R, Dasgupta P, Folke C, Holling CS, Jansson B-O, Levin S, Mäler K-G, Perrings C, Pimentel D.  (1995) Economic-Growth, Carrying-Capacity, and the Environment. Science 268: 520–521.</ref>.<br> 
Precisely, the consideration of the carrying capacity of the estuarine ecosystem and ecological thresholds <ref>D, Reynolds J, Turner M, Weathers K, Wiens J (2006) Ecological thresholds: The key to successful environmental management or an important concept with no practical application? Ecosystems 9: 1–13.</ref> has been instrumental in putting together the restoration plan of the Scheldt estuary, in particular measuring the importance of re-creating tidal systems. In the 1990s, it was felt that tidal wetland restoration would be necessary in order to compensate loss of habitat <ref name="Eertman 2002">Eertman RHM, Kornman BA, Stikvoort E, Verbeek H (2002) Restoration of the Sieperda tidal marsh in the Scheldt estuary, the Netherlands. Restoration Ecol 10: 438–449.</ref>. <p>
In combination with a master plan to protect the population from storm surges, an opportunity arose to restore areas under tidal influence. One specific option of combining safety and ecology was the creation of flood control areas under the influence of a controlled reduced tide (CRT) <ref name="Maris2007">Maris T, Cox T, Temmerman S, De Vleeschauwer P, Van Damme S, De Mulder T, Van den Bergh E, Meire P (2007) Tuning the tide: creating ecological conditions for tidal marsh development in a flood control area. Hydrobiologia 588: 31–34.</ref>. These specific areas differ in many ways from fully tidal areas but can fulfil important ecological functions with effects on aeration, sedimentation <ref name="ten Brinke">Ten Brinke WBM, Dronkers J (1993) Physical and biotic aspects of fine-sediment import in the Oosterschelde tidal basin (The Netherlands).Neth J Sea Res 31: 19–36.</ref><ref name="Bolle 2010">Bolle A, Bing Wang Z, Amos C, De Ronde J (2010) The influence of changes in tidal asymmetry on residual sediment transport in the Western Scheldt. Cont Shelf Res 30: 871–882.</ref> nitrification, [[denitrification]], and [[primary production]] in the estuary <ref name="Billen 2005">Billen G, Garnier J, Rousseau V (2005) Nutrient fluxes and water quality in the drainage network of the Scheldt basin over the last 50 years. Hydrobiologia 540: 47–67.</ref>. Opportunities for ecological development within a CRT have been investigated for a specific case. The ecology within a CRT was shown to be very case specific, depending e.g. on the morphology of the area, the sluice design and the local water quality <ref>[http://www.vliz.be/imis/imis.php?module=ref&refid=107942 Van Den Berghe E, Van Damme S, Graveland J, De Jong D, Baten I, Meire P (2005) Ecological rehabilitation of the Schelde Estuary (The Netherlands-Belgium; Northwest Europe): Linking ecology, safety against floods, and accessibility for port development. Restoration Ecol 13: 204–214.]</ref>. Depending on the sluice design, water quality can be improved and sedimentation can be influenced. A scientific approach to the management of these sensitive areas made it possible to design CRTs with a rich habitat variation <ref name="Maris 2007">Maris T, Cox T, Temmerman S, De Vleeschauwer P, Van Damme S, De Mulder T, Van den Bergh E, Meire P (2007) Tuning the tide: creating ecological conditions for tidal marsh development in a flood control area. Hydrobiologia 588: 31–34.</ref>. Some ideas for the future restoration of estuaries world-wide should emanate from that approach. Any future estuarine management plan should take into consideration the type and the proportion of each habitats which needs to be (re)-created in order to provide the ecosystem with expected functionalities <ref name="Diaz2004">Diaz RJ, Solan M, Valente RM (2004) A review of approaches for classifying benthic habitats and evaluating habitat quality. J Environ Manage 73: 165–181.</ref>. In parallel, expected goods and services to be provided should be adapted <ref name="Folke 2002">Folke C, Carpenter S, Elmqvist T, Gunderson L, Holling CS, Walker B, Bengtsson J, Berkes F, Colding J, Danell K, Falkenmark M, Gordon L, Kasperson R, Kautsky N, Kinzig A, Levin S, Mäler KG, Moberg F, Ohlsson L, Olsson P, Ostrom E, Reid W, Rockström, Savenije H, Svedin U (2002) Resilience and sustainable development: Building adaptive capacity in a world of transformations. Ambio 31: 437–440.</ref><ref name="Hughes 2007"> Hughes TP, Gunderson LH, Folke C, Baird AH, Bellwood D, Berkes F, Crona B, Helfgott A, Leslie H, Norberg J, Nystram M, Olsson P, Asterblom H, Scheffer M, Schuttenberg H, Steneck RS, Tenga M, Troell M, Walker B, Wilson J, Worm B. (2007) Adaptive management of the great barrier reef and the Grand Canyon world heritage areas. Ambio 36: 586–592.</ref>. The main requirement to sustain such measures is that they should ensure resilience and adaptability <ref name = Peterson2010>Peterson GD, Allen CR, Holling CS (2010) Ecological resilience, biodiversity and scale. Ecosystems 1: 6–18. </ref>. So, planning should include actions to mitigate or to reverse the local effects of [[climate change]] (e.g. [[sea level rise]]) and slow down the global change (e.g. through CO<sub>2</sub> sequestration).

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=== The Seine ===

All of the sites considered earlier in this article have benefited from management schemes in order to re-establish some of the lost ecological functions: in the [[Elbe estuary|Elbe]], the sediment dynamics, in the Scheldt, the control of floods, in the Humber, the restoration of specified ecological processes. In the Seine the restoration process was started quite differently. Compensation measures were implemented in the late 1990s in response to the extension of Le Havre port facilities. The construction of “Port 2000” was the occasion for managers and politicians to stress the importance of research for reaching “a balance between the development of economic objectives and the protection of natural aquatic environments towards an integrated management of the estuary”. The new harbour installations required the reclamation of existing [[wetlands]] <ref name="Ducrotoy2008">Ducrotoy JP, Dauvin JC (2008) Spatio-temporal scales in estuarine conservation and restoration. Mar Pollut Bull 57: 208–218. </ref>. Such an operation presented threats for safeguarding the sedimentary balance in the estuary and the future of mudflats. Decision makers decided that accompanying measures should be taken to minimize the hydro-sedimentary impact and to rehabilitate threatened intertidal mudflats durably. Various options were selected after mathematical modelling of circulation patterns of sediments in the estuary. The ones which were adopted consisted mainly in restoring one damaged mudflat, building a resting place for birds on a sand dune and constructing a small island, also to be a refuge for birds. Some habitats were re-created on part of the land claimed from the estuary with a view to facilitating the growth of charismatic plants <ref name="Scherrer">Scherrer P, Galichon P (2002) Port 2000—La combinaison d’un projet portuaire et d’un projet environnemental d’amorce de réhabilitation de l’Estuaire de la Seine. VIèmes Journées Nationales Génie Civil-Génie Côtier, Anglet, France, 15–17 Mai 2002, Paralia: 499–511.</ref><ref name ="Dauvin">Dauvin JC, Desroy N, Janson AL, Vallet C, Duhamel S (2006) Recent changes in estuarine benthic and suprabenthic communities resulting from the development of harbour infrastructure. Mar Pollut Bull 53: 80–90.</ref><ref name ="Port Autonome du Havre">Port Autonome du Havre (2007). Port 2000 and the river Seine estuary. PAH, le Havre: 26 pp.</ref>. The relevance of future experimental restoration measures will depend on the adequacy of scientific research in helping to build a long term vision of the estuary.
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== Integrated management plans ==
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{|align="center" style="text-align:center; font-size:85%" 
|[[Image:A model plan for the restauration of an estuary.jpg|550px]]
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|Figure 2: A model plan for the restoration of an estuary
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The piecemeal application of present European environmental legislation has not been sufficient to change the negative trends in the considered estuaries. Integrative management plans are still required at the scale of each estuary <ref name = Harris2006>Harris JA, Hobbs RJ, Higgs E, Aronson J (2006) Ecological restoration and global climate change. Restoration Ecol 14: 170–176.</ref>. Such a model plan is shown on figure 2. What is interesting is that despite the different managerial approaches applied in the various countries, all actions included some degree of ecological restoration of habitats. Such actions involved more or less large-scale engineering work. From comparing these various managerial approaches in the different estuaries, it appears that only conservation objectives can translate the aim to reduce negative developments. It would seem that the best way to formulate such objectives is in computing and calculating surfaces of the different habitats necessary to sustain the resilience of the ecosystem <ref name ="Folke">Folke C, Carpenter S, Elmqvist T, Gunderson L, Holling CS, Walker B, Bengtsson J, Berkes F, Colding J, Danell K, Falkenmark M, Gordon L, Kasperson R, Kautsky N, Kinzig A, Levin S, Mäler KG, Moberg F, Ohlsson L, Olsson P, Ostrom E, Reid W, Rockström, Savenije H, Svedin U (2002) Resilience and sustainable development: Building adaptive capacity in a world of transformations. Ambio 31: 437–440.</ref><ref name="Gunderson">Gunderson L and Folke C (2005) Resilience—Now more than ever. EcolSoc 10: 22.</ref>, including geomorphological, hydrodynamic, ecological and quality aspects. The approach shown on figure 3 gives the possibility to sustain each estuary in a healthy state to reduce management costs and increase benefits from goods and services obtained from them. In order to do so, a holistic approach is needed where the system characteristics are considered in such a way that negative developments are stopped or at least slowed down. This requires a major investment in research to better understand the systems functioning and the interactions between the different compartments, including socio-economics, identify services and calculate surface of habitat needed for delivering the required services and providing the expected goods to humans.
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{|align="center" style="text-align:center; font-size:85%" 
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|Figure 3: A Model plan for sustaining an estuary in a healthy state
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In order to define strategies compatible with conservation and sustainable development at the local, regional and European levels, environmental aspects must be integrated in the management of estuaries, which must rely on thorough collaboration between and mutual understanding of all actors and stakeholders. Resting on a rigorous scientific approach, restoring ecological functionalities in an estuary is dependent on efficient procedures of socio-ecological evaluation including a methodology to assess the ecological quality of systems considered <ref name ="Bingham1995">Bingham G, Bishop R, Brody M, Bromley D, Clark E, Cooper W, Costanza R, Hale T, Hayden G, Kellert S, Norgaard R, Norton B, Payne J, Russell C, Suter G (1995) Issues in Ecosystem Valuation— Improving Information for Decision-Making. Ecol Econ 14: 73–90.</ref><ref name ="Costanza1998">Costanza R, d’Arge R, de Groot R, Farber S, Grasso M, Hannon B, Limburg K, Naeem S, O’Neill RV, Paruelo J, Raskin RG, Sutton P, van den Belt M (1998) The value of ecosystem services: putting the issues in perspective. Ecol Econ 25: 67–72.</ref><ref name="de Groot2002">de Groot R, Wilson MA, Boumans RMJ (2002) A typology for classification, description and valuation of ecosystem functions, goods and services. Ecol Econ 41:393–408.</ref>. For making interdisciplinarity work, socio-economics need to be considered in the early stages of the elaboration of any restoration programme.<p>
Putting the project in a scientific perspective implies the application of fundamentals of [[Topic:Ecology|ecology]]. Because of the popularity of certain concepts, including biodiversity, productivity, etc., definition and use of important terms may have been misinterpreted <ref name="Ducrotoy2008">Ducrotoy JP, Yanagi T (2008) Tools and concepts on ecological quality of coastal and estuarine environments. Mar Pollut Bull 57: 1–2.</ref>. For example, most often, the general public thinks that biodiversity is at the basis of robust and productive ecosystems. Recently, Elliott & Quintino (2007) <ref name="Elliot2007">Elliott M, Quintino V (2007) The estuarine quality paradox, environmental homeostasis and the difficulty of detecting anthropogenic stress in naturally stressed areas. Mar Pollut Bull 54: 640–645.</ref> have put into light the quality paradox of estuaries, where poor species richness supports high production and stability <ref>Holling, C.S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics 4:1-23.</ref><ref name ="Peterson2010">Peterson GD, Allen CR, Holling CS (2010) Ecological resilience, biodiversity and scale. Ecosystems 1: 6–18.</ref>.<p>
The concept of habitat is therefore essential as a species might disappear but a habitat remains available for [[Ecological thresholds and regime shifts|shifting species]]. Unfortunately, European and national legislation aimed at protecting habitats are species based, locked by conservation management. With the arrival of “new” species, whether they will move in response to the [[climate change|climatic change]] or they were [[Non-native species invasions|introduced artificially]], conditions should be made to avoid “fossilisation” of protected habitats. It might be necessary to accommodate shifts in spatial distribution and alien species. However, one may ask whether the legislative framework is fit for purpose when habitats will need to be adapted to changing biophysical conditions <ref name="Harris 2006">Harris JA, Hobbs RJ, Higgs E, Aronson J (2006) Ecological restoration and global climate change. Restoration Ecol 14: 170–176.</ref>. Breakdown in geographical barriers or deliberate and inadvertent transport of species could be at the origin of new "emerging" ecosystems, of which the functional characteristics are unknown today. From all examples given, it has been shown that it is impossible to freeze an ecosystem at a particular stage of its evolution and that it is further impossible to return backward in time. Fundamental research needs to address the issue of better understanding future shifts in ecological niches. Rigorous monitoring programs, resting on a relevant choice of indicators (table 1), should be linked to research and data used more efficiently and on the long-term <ref name = "Ducrotoy 2010b">Ducrotoy JP (2010) The use of biotopes in assessing the environmental quality of tidal estuaries in Europe. EstuarCoastShelfSci 86: 317–321</ref>.
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{|width="690px" Align="center" style="valign: top" 
|
{|border="1" cellspacing="0" Cellpadding= "5" 
| '''Scientific area'''
| '''Indicator'''
| '''Response'''
| '''Tools'''
|- valign="top"
|rowspan="2"| 1. Populations dynamics
|Biological diversity and community structure <br> Population numbers and turn over 
|Numbers equivalent to those found for resistance in normal disturbance conditions
|Diversity indices <br> Life tables <br> Multivariate statistics
|- valign="top"
|Distribution of plant and animal propagules <br> Animals circulation
|No physical or chemical break in connectivity and migration corridors within and between habitats
|Water quality  compatible with organisms survival
|- valign="top"
|rowspan="2"| 2. Biogeography
|Species spatial distribution 
|Species spatial distribution  extension compatible with ecosystems dynamical balance 
|Long-term monitoring at the eco-region scale
|- valign="top"
|Alien invasive or introduced species
|Absent or low numbers compatible with the integrity of other species, the habitat or the ecosystem
|Integrated surveillance 
|- valign="top"
|3. Functional ecology 
|Communities functioning <br> Algal or invertebrate functional groups 
|Sustainable on the long -term <br> All functional groups are represented
|Indices <br> Trophic structure
|- valign="top"
|4. Eco-morphology
|Spatial distribution and quantitative make-up of biotopes (bio-sedimentary facies) and/or habitats <br> Functional relations between biotopes
|Ecosystem made of all main biotopes in sufficient quantity in normal physical and chemical conditions
|Sedimentary and biological parameters to be compared to reference conditions
|- valign="top"
|5. Sato-Umi eco-hydrological
|Biogeochemical  dynamics of nutriments from watershed to estuary and coastal environment approach
|Hydrological conditions  not modified by anthropic activities <br> Physical and chemical quality of water masses unaltered
|Mathematical modelling of primary production <br> Light incidence in water column
|- valign="top"
|rowspan="2"|6. Patrimonial approach 
|Protected and threatened species
|Incorporated in changing ecosystem dynamics
|Routine monitoring
|- valign="top"
|Importance of protected  areas 
|Sustained or expanded according to system’s dynamics
|GIS
|- valign="top"
|rowspan="3"|7. Natural resources exploitation
|Genetic diversity of cultivated and wild species of fish, molluscs and shellfish
|Not affected <br> Acknowledgement of  socio-economic value 
|DNA sequencing 
|- valign="top"
|Integrated sustainable management of aquaculture and fisheries  (from river to sea)
|Meeting socio-economic requirements and constraints (from local to global)
|Fish populations dynamics studies <br> Biomarkers
|- valign="top"
|Sustainable management of exploited species  and /or des products (for example biopharmaceuticals)
|Potential intact
|Biodiversity <br> Population dynamics of exploited or exploitable species <br> Market economy
|- valign="top"
|8. Anthropic impacts 
|Existent and potential threats in and out socio-ecosystem
|Eliminated, reduced, attenuated or compensated <br> Positive evolution of biodiversity with regard to  climate change
|Pollution assessment in water, sediment and bios <br> Biomonitors <br> Pressure integrated indicators 
|}
|- align="center" style="text-align:center; font-size:85%" 
|Table 1: Indicators and tools for estuarine ecological restoration
|}

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==The way forward==

Climate change will affect managers' views on the permanence of estuarine socio-ecosystems. In the future, the restoration of damaged habitats will be instrumental in adapting socio-economic activities <ref name="Folke2002">Folke C, Carpenter S, Elmqvist T, Gunderson L, Holling CS, Walker B, Bengtsson J, Berkes F, Colding J, Danell K, Falkenmark M, Gordon L, Kasperson R, Kautsky N, Kinzig A, Levin S, Mäler KG, Moberg F, Ohlsson L, Olsson P, Ostrom E, Reid W, Rockström, Savenije H, Svedin U (2002) Resilience and sustainable development: Building adaptive capacity in a world of transformations. Ambio 31: 437–440.</ref><ref name="Hughes2007">Hughes TP, Gunderson LH, Folke C, Baird AH, Bellwood D, Berkes F, Crona B, Helfgott A, Leslie H, Norberg J, Nystram M, Olsson P, Asterblom H, Scheffer M, Schuttenberg H, Steneck RS, Tenga M, Troell M, Walker B, Wilson J, Worm B. (2007) Adaptive management of the great barrier reef and the Grand Canyon world heritage areas. Ambio 36: 586–592.</ref> to changing environmental conditions <ref name ="Diaz2004">Diaz RJ, Solan M, Valente RM (2004) A review of approaches for classifying benthic habitats and evaluating habitat quality. J Environ Manage 73: 165–181.</ref>. In this context, [[sea level rise]], presently estimated at 30 cm per century and expected to increase, according to the prognosis of [http://www.ipcc.ch/ IPCC], in the second part of the century, is a paramount challenge. Besides the enlargement of tidal capacity, a reduction of the cross-section profile at the mouth of the estuaries ought to hold back part of the tidal energy in the event of a storm surge. What will be the implications of such events for estuarine ecological restoration? Climate change will make "[[habitat|habitats]]" of interest more fragile and less resilient. The Scheldt example has shown that a patrimonial view of ecosystems is not necessarily compatible with promoting new functions in an estuary. The Seine compensation measures showed how important habitats are as there is a need to allow species to adapt to new biophysical conditions. Nevertheless, ecosystems are dynamical and restoration needs to focus on ecosystems (and how they function), not species <ref name="Elliot2007">Elliott M, Quintino V (2007) The estuarine quality paradox, environmental homeostasis and the difficulty of detecting anthropogenic stress in naturally stressed areas. Mar Pollut Bull 54: 640–645.</ref>.<p> 
In order to get sustainable and successful management, harmonisation is required within and between sectors, stakeholders, regulators, mediums, estuaries, regions, countries, outcomes and implementation. This is because North-West Europe estuaries are regarded as multi-user spaces and so there are many things which need to be managed (and by whom) <ref name="Eliot 2010"/>: <p>
:* habitats (nature conservation agencies), 
:* environmental quality (Environmental Protection Agency-type organisations), 
:* water space usage (port authorities), 
:* navigation (port authorities), 
:* infrastructure (municipalities/federal state), 
:* energy extraction (private companies), 
:* biological extractions (fisheries bodies), 
:* estuarine water extraction (private energy companies), 
:* upstream water abstraction (water supply companies), 
:* land space usage (municipalities/federal state), 
:* erosion and flooding control (EPA, municipalities etc),
:* industry (EPA and private companies) 
:* and recreation and tourism (agencies).
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Restoring [[Ecosystem function|functions at ecosystem]] level will undoubtedly help guarantee assets to human societies which depend on them. Ensuring resilience and adaptability, will allow adjusting goods and services both to new environmental conditions and to emerging human needs. But, over and above, integrated management of estuaries will be essential in adapting to local changing conditions (e.g. sea level rise) and slowing down climate change at global level. It is why, in the future, participation of local communities will be essential for the success of measures taken. Communicating with existing groups will help making visible actions taken and creating synergies with other development plans. Research and education clearly stand out as a means to achieve governance.
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==Related articles==
:[[Estuarine ecosystems]]
:[[Habitat]]
:[[Threats to the coastal zone]]
:[[Marine habitats and ecosystems]]
:[[Effects of fisheries on marine biodiversity]] 
:[[Natural variability and change in coastal ecosystems]]
:[[Principles of conservation, rehabilitation and restoration of estuarine and coastal habitats]]
:[[Morphology of estuaries]]
:[[Tidal asymmetry and tidal basin morphodynamics]]


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== References ==
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[[Category:Estuaries and tidal rivers]]
[[Category:Coastal and marine ecosystems]]   
[[Category:Restoration of coastal and marine zones]]
[[Category:Integrated coastal zone management]]

{{Authorwithoutaccount
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|AuthorFullName=Ducrotoy, Jean-Paul}}
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