estuarine conservation and restoration: the somme and the seine case studies (english channel,...

Marine Pollution Bulletin 57 (2008) 208–218

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Marine Pollution Bulletin

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Estuarine conservation and restoration: The Somme and the Seine case studies(English Channel, France)

Jean-Paul Ducrotoy a,*, Jean-Claude Dauvin b

a University of Hull, Hull HU6 7RX, England, United Kingdomb Station Marine de Wimereux, Université des Sciences et Technologies de Lille, FRE CNRS 2816 ELICO, BP 80, 28 Avenue Foch, F-62930 Wimereux, France

a r t i c l e i n f o

Keywords:
RestorationHabitatsBiotopesEstuariesSeineSomme
0025-326X/$ - see front matter � 2008 Elsevier Ltd.doi:10.1016/j.marpolbul.2008.04.031

* Corresponding author. Tel.: +33 (0) 3 22 23 80 74E-mail address: [email protected] (J.-P. Ducroto

a b s t r a c t

Megatidal estuaries such as the Seine and the Somme (North-Western France) are rather well delimitedand human impacts on them are well understood. Since the middle of the 19th Century, there has been aslow but irreversible degradation of the state of these English Channel estuaries. However, current con-servation and restoration strategies tend to freeze habitats in a particular state, their status being defined,most often, through a patrimonial or utilitarian approach. Connectedness between biotopes (sensu hab-itat + community) has a tendency to be neglected, especially with regard to main ecological gradients, i.e.,salinity. In this paper, evaluation methodologies are proposed with the intention of assessing changes toecosystem functions, under anthropogenic disturbance, controlled or otherwise. The Seine (a heavilyindustrialised ecosystem) is compared to the Somme (considered here for its pseudo-natural features)in order to discriminate between oceanic processes (siltation and plugging of estuaries) and anthropo-genic influences. Preservation and restoration of habitats rely on a robust scientific methodology. Themulti-scale approach adopted in the projects presented here relies on sensitive socio-ecological assess-ment procedures, tools for evaluating ecological quality, and well-built monitoring programmes basedupon pertinent indicators. Such managerial tools were used to refine strategies and make them compat-ible with the sustainable co-development of resources in a European context. This paper demonstrateshow scientists were able to acquire and apply knowledge in the field of rehabilitation and restoration.Jointly with managers and policy-makers, they have brought scientific information and socio-economicstogether in order to answer questions about the restoration of sites or habitats and to anticipate futurepropositions in the spirit of Integrated Coastal Zone Management (ICZM).

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1. Introduction

Amongst coastal ecosystems, estuaries need particular atten-tion as interfaces between fresh and marine waters and the atmo-sphere. They are defined as zones of transition where emerges awater court which discharges into the sea. They are closely con-nected to the ecosystems adjacent to them. Such interfaces areknown as ecoclines (see Attrill and Rundle, 2002). Estuarine eco-clines are characterised by a double gradient of salinity changesfrom the freshwater to the sea, and from the sea to the river. Inestuaries there are also rapid flux of materials and organisms. Theyperform various functions, including mediating water flows, accu-mulating sediments and organic matter, processing nutrients, fer-tilising adjacent coastal waters and providing opportunities forrecreation. This is why the restoration of habitats and ecologicalfunctions requires a broad multi-disciplinary reflexion on the def-inition of objectives as well as of methods. A true consensus on the

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.y).

necessity of returning lost estuarine areas to the sea is building upin Europe, thanks to adopting an ecosystemic approach and bydeveloping interdisciplinary synergies. Most of the time, function-alities are still found in an estuary, but more or less degraded, asshown in the two case studies presented here.

The coast of the eastern part of the English Channel in North-Western France is bordered by several important megatidal estuar-ies. All of them have evolved quickly at the ecological scale, due tonatural influences but also because of human influences. Naturally,such drowned valleys have a tendency to silt up due to sands car-ried in by the tide in relation to the current Flandrian marine trans-gression. Human activities have resulted in very different impactson hydrology, and on the volume of water coming into the estuar-ies, which have produced a reduction of the intertidal zones andmud flats, and an increase of shore bars and salt marshes accordingto the way the estuaries have been managed, whether for naviga-tion and industry or for agriculture and fisheries. The Seine estuaryfalls in the first category, where, since the mid 19th Century, theharbours of Le Havre and Rouen have dominated all other activitiesin the area (Dauvin, 2006a). The case of the Somme estuary (Bay of

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Somme) is different. Land in the Somme was mostly reclaimed foragriculture, while accessibility was managed in an attempt to keepfishing harbours at St. Valery and Le Crotoy operating (Ducrotoy,1998). In both cases, the estuaries have been much reduced in sizeand have lost a great proportion of their intertidal areas.

Recently, confronting an emerging demand from non govern-mental organisations and pressure groups (such as hunters andfishermen) and, to a lesser degree, from the public for ‘‘natural’’areas, managers and policy-makers have required scientist infor-mation on the feasibility of restoring some of the lost or damagedestuarine habitats caused by, for instance, the construction ofdykes or because of pollution.

The Port 2000 project (extension of Le Havre harbour) was strik-ing for the extent of the public debate (a first in France) and can beconsidered a posteriori as having provided an opportunity to thinkabout the global environmental situation of the Seine estuary. Infact, this major development project was the impulse for the crea-tion of both the Global Management Plan for the Estuary and theestablishment of the Estuary Council, in which hopes for a betterimplementation of sustainable development practices in this estu-arine zone are founded. In 2004, the Estuary Council asked theSeine Normandy Water Agency (SNWA) to coordinate a forecaststudy concerning the perspectives for restoring the environmentalfunctions of the Seine estuary by 2025.

In the Somme, ecotourism is developing fast. In order to managethe environment in a sustainable way, local authorities have in-stalled a management body, called Syndicat Mixte pour l’Aménage-ment de la Côte Picarde (SMACOPI). The syndicate claims restoringand rehabilitating estuarine features as well as opening new facil-ities to tourists in the area.

The Seine-Aval programme, created in 1995, has been able inthe third stage (2004–2006) to bring together people having ac-quired competences on ecological restoration and the main man-agers of the Seine such as the independent port authorities (PortAutonome du Havre: PAH, and Port Autonome de Rouen, PAR),and the SNWA in order for them to come to an agreement. In the

Fig. 1. Location of the Seine Estuary and the Bai

Somme, the PICCEL (PICardie: Connaissance et Exploitation du Lit-toral – Knowledge and exploitation of the coast) programme waslaunched in 2003, to provide scientific information on possiblechanges in ecology of the estuary in response to the climatic globalchange.

The secondary objectives of the above programmes were multi-ple and included:

1. To gather knowledge on the natural environments and otherecosystems in the estuaries.

2. To examine the potentials for restoration of the habitats con-cerned in order to restore ecological quality.

3. To suggest long-term actions in order to renovate the estuaryfrom an ecological point of view.

4. To follow-up any required operations.

To begin with, the paper introduces the sites: the Seine and theSomme estuaries. It then considers the methods to be applied.Stakeholders are presented and examples of past restoration expe-riences are commented on. The discussion opens out onto propos-als for better-integrated operations in the future.

2. Site presentation

2.1. Seine estuary

The Seine estuary is the largest estuary in the English Channel,located in its Eastern part (Fig. 1). Its geographic zone of influenceruns from just upstream of the Poses dam – some 160 km up-stream Le Havre, at the limit of the tidal penetration into the estu-ary – to the eastern part of the Bay of Seine (Dauvin, 2006a). Thiszone can be divided into three sections (Fig. 2): the fluvial, or up-stream, estuary from Poses to Tancarville Bridge; the middle estu-ary between Tancarville Bridge and Honfleur; and the marine, ordownstream, estuary which opens into the Channel. The freshwa-ter flow of the river at Poses is relatively small (480 m3 s�1 on

e de Somme in France (from Dauvin, 2007).

Fig. 2. Detailed maps of the Seine Estuary, showing the various transitional water masses –T1a and T1b are freshwater tidal, T2 is saline tidal, T3 is the open estuary.

210 J.-P. Ducrotoy, J.-C. Dauvin / Marine Pollution Bulletin 57 (2008) 208–218

average over the last 30 years), with high water volumes over2220 m3 s�1 (autumn/winter) and low water flow under100 m3 s�1 (at the end of summer in September). Hydrodynamicsare heavily influenced by the tide, which can reach nearly 8 m inmagnitude during the spring tides downstream of Honfleur. Thismegatidal regime causes a zone of maximum turbidity, which is lo-cated in the mixing zone (middle estuary) between the marine andfluvial sections of the estuary (Dauvin, 2006a). The Seine valley andits estuary are of major economic importance for France, notablydue to the presence of two maritime ports. The Seine estuary liesat the discharge point of a watershed area covering 79,000 km2.This area is home to 16 million people, and accounts for 50% ofthe river traffic in France, 40% of the country’s economic activity,and 30% of its agricultural activities. In addition to the Greater Parisarea with more than 10 million inhabitants, who contribute heav-ily to the Seine estuary’s upstream inputs (mainly contaminantsand waste waters), there are also two other major river settlements– Rouen with 4,00,000 inhabitants and Le Havre with 2,80,000inhabitants – and two maritime ports of international importance– the independent Port Autonome de Rouen (PAR) and Port Auto-nome du Havre (PAH).

At the beginning of the 19th Century, the outer Seine estuaryextended up to half way between Rouen and the sea. Since the sec-ond half of the century, construction of dykes and seawalls haveimproved shipping conditions and have permitted bigger and big-ger vessels to reach Rouen city. After World War II, mathematicalmodels were instrumental in the building of an auto-dredgingchannel. Works ended by the end of the 1970s. In the downstreampart of the estuary of the Seine, the damming of the Seine duringthe 19th Century created a deep fixed channel. This has been main-tained by dredging. The surface of the intertidal zone has been dra-matically reduced from more than 130 km2 in 1850 to less than30 km2 at the beginning of the 21st Century (Dauvin and Desroy,

2005). Laterally, sediments clogged up and were colonized by veg-etation which became quickly climatic, primarily made up of reedbeds, dotted by ponds dug for hunting. In the lower part of theestuary, fringes accommodate halophilous plants and mud flat re-mains. A network of channels is still present and helps to maintaincertain estuarine characteristics within the reed beds which havetended to become an over-simplified ecosystem (Alard, 2002), withtime and progressive silting of the zone. Gaps have recently (2005)been opened in dykes to favour links between the estuarine envi-ronment and salt marshes, in view of future attempts at re-estuari-sation of selected areas. Meadows and thickets of willow occupyspaces withdrawn from the estuary, beside vast industrial and ur-ban parks (Dauvin et al., 2006; Dauvin, 2006a). Along many pene-trating routes (roads, ways, paths), a terrestrial flora colonized andsettled. Upstream of the estuary, old meanders of the river becamecontained and evolved into marshes (Robert Lafite, personal com-munication). Wet meadows occupy old meanders of the Seineand ‘alluvia’ of the Vernier marsh as well as small basin tributaries.Fresh water originates from the aquifer of the Pays de Caux andfrom riverine and atmospheric contributions. These various inputsof freshwater resulted in an aquatic system extremely parcelledout and compartmentalised with little communication betweenfresh water, estuarine and marine systems (Alard, 2002; Dauvin,2002, 2006b; Dauvin and Desroy, 2005).

2.2. The Bay of Somme

The Bay of Somme is found within the region of Picardie (Fig. 1).It is a large megatidal ecosystem, characterised by a rather lowfresh water input (30 m3 s�1, mainly from the river Somme) andstrong hydrodynamic processes. Spring tides reach a height of9.80 m and the salinity on mud flats rarely drops below 25. A shorebar, consisting of flint clasts, derived from the chalk cliffs (Pays de


Caux) to the south, extends north across the mouth of the bayaltering the tidal prism and channel positions. The estuary is char-acterised by a strong input of marine lithoclastic sands to the cen-tral part of the bay. Influxes of terrestrial sediments from theadjacent fluvial catchment area augment the marine sedimenta-tion profile. In particular, increased siltation is taking part in thesheltered areas of the bay.

The Bay of Somme has been largely reduced in size throughoutthe last three centuries, measuring from more than 500 km2 toabout 72 km2 of intertidal sands and muds. Various historicaland recent attempts to control processes have had a number ofpotentially detrimental effects on morpho-sedimentary evolution-ary trends within the system. The building of seawalls and dykesaccelerated the natural evolution of the estuary due to the Flandri-an transgression, increasingly bringing in sedimentary material(Ducrotoy, 1998). As a result of the estuarine dynamics, a twofoldreduction of the true estuarine areas has taken place: marine sandshave been brought into the central parts and salt marshes arespreading in the upper reaches. Changes in the benthic communi-ties have been described in relation to changes in the sedimentarydynamics and in conjunction with eutrophication problems due toorganic enrichment from agriculture and municipal wastes (Ducro-toy and Ibanez, 2003). The rapid erosion of the shingle bar causedmajor engineering problems and huge investments are currently

Fig. 3. Main designated areas for protection in the Bay of Somme (Fran

being made to stabilise its position and re-build the shingle barprotecting the southern part of the estuary. Some concern has beenexpressed regarding the extraction of shingle and gravel just be-hind the bar because of the potential risk of weakening itsencroaching to the coast. The main socio-economic activities con-sist of traditional practices such as hunting, cockle and inshorefishing and harvesting of vegetable products. In the surroundingpolders, traditional agriculture is surviving. For the past few dec-ades, tourism has developed on a large scale and has helped reor-ganize entirely the local economy (Fig. 4).

3. Scientific, social and administrative background

3.1. The Seine-Aval programme

Despite the major importance of the estuary nationally and itshighly degraded condition, it wasn’t until the 1990s and the begin-ning of the Seine-Aval programme that the knowledge base relatedto the Seine estuary began to grow significantly. The programmewas organised in three phases (Dauvin, 2006a).

In the first phase (1995–2000), the objectives were: (i) to pro-vide the knowledge needed to understand how the Seine estuaryfunctioned; (ii) to establish priorities in order to optimize theinvestments needed to restore water quality; (iii) to build scientific

ce) – terms are explained in text (adapted from SMACOPI, 2006).

Fig. 4. Main geomorphological characteristics of the Bay of Somme and location of the Dien River, Spartina control area and Blanquetaque wetlands.


databases that would allow the impact of hydrologicaldevelopment projects to be estimated; and (iv) to supply theinformation needed to reconcile the different users of the estuary,particularly those involved in fishing, industry, tourism and leisureactivities.

In its second phase (2000–2003), Seine-Aval sought to make theprogramme more operational. To this end, it played a central rolein implementing global management policies for the Seine estuary.Four new multi-disciplinary topics were developed: (i) to analyzethe chemical and microbial status of the estuary; (ii) to establishthe role of the zones adjacent to the estuary, particularly the inter-tidal mudflats, in the estuarine functions and economy; (iii) tostudy the disturbances in the estuary as well as their ecologicaland economic consequences on fishing resources; and (iv) toexamine the status of the estuary in terms of eutrophication, or-ganic matter degradation and nutrient retention.

During, the 3rd phase (2004–2006), the program continued toacquire the knowledge needed to better understand the problemsmentioned above, by pushing for more research devoted to under-standing and modelling the geomorphological evolution of theestuary because it has a strong influence on all estuarine functions.The program developed tools and worked to apply the results ofscientific research. The value of these results can be underscoredby sharing scientific data and knowledge, and by proposing tools,including report cards and indicators, numerical models and dat-abases, and methodological guides.

Through the 3 stages of Seine-Aval, scientific knowledge has in-creased dramatically. The main stakeholders include PAH, PAR,SNWA, CCIH (Chambre de Commerce et d’Industrie du Havre),the Regions of Haute and Basse Normandie.

3.2. The PICCEL programme

The PICCEL (PICardie: Connaissance and Exploitation du Littoral– Knowledge and exploitation of the coast) programme waslaunched in 2003 (Ducrotoy, in press). Its main objective is to con-

tribute to the understanding of the natural variability of the coastand estuaries of Picardie (France) in the context of the globalchange. A new computerised data bank was installed in 2003 andstored on GIS. Available data on the coast of Picardie has been col-lected and stored. In order to get a coherent overview of coastalecosystems, a new sampling grid was established, making easythe geo-referencing of data. It was also made compatible with mostpre-existing transect lines. The strength of the programme lies inits ability to create data products, in particular multi-layered maps.Such tools are most useful to fisheries and nature reserves manag-ers and policy-makers. The dissemination of scientific informationand outreach activities are important parts of the programme. Be-cause of progress in recent decades to collect valid scientific dataon the coast of Picardie, establishing an adequate interdisciplinaryframework with the corresponding human, institutional and finan-cial resources was vital. This is why PICCEL is open to fundamentalresearch. Such research, whether basic or applied, must be shapedto deal with the uncertainty that characterises such highly com-plex systems with a dominance of chaotic behaviours. In fact,one of the most difficult issues is relating scientific findings to hu-man activities and issues. Collaboration with colleagues from uni-versities in anthropology, economy and geography is beinginitiated.

The main stakeholders include the Region of Picardie, theDepartment of Somme and the SMACOPI.

4. Nature reserves and the patrimonial approach toconservation

A coherent policy of wetland conservation must be foundedboth on an ecological evaluation and on the appropriate protectionand management tools. The Parc Naturel Regional (PNR) des Bou-cles de la Seine Normande (PNRBSN) is located aside the fluvialpart of the Seine estuary between the Tancarville Bridge and thedownstream part of Rouen. In the Bay of Somme, a PNR has beenproposed and is currently under consideration.


In the lower Seine valley, two nature reserves exist: (i) The re-serve of Mannerville was created in 1994 on 93 ha; (ii) The reserveof the estuary was created in 1999 and extended in 2004 to reach8528 ha. The reserve of the estuary is managed by the association,‘La Maison de l’Estuaire’. It protects most of the mudflats and reedbeds, as well as much of the marshlands. It was extended followinga statement made by the European Court of Justice on the 18th ofmarch 1999. France was given a formal notice to extend the area ofthe European Special Area and to improve its management.

One important nature reserve covers a large part of the Sommeestuary and includes salt marshes, mudflats and sand banks. It islocated in the northern part of the bay, adjacent to the Parc Orni-thologique du Marquenterre, a bird reserve (Fig. 3).

Hunting reserves have been established on public coastal landin both the Seine and the Somme estuaries at the instigation of var-ious associations for hunting. In France, administrative orders onbiotope protection set out the measures to preserve the biotopesof protected species. Biotope orders have been made in the lowerSeine and in the Somme. Natural zones of special interest for theirecology, flora and fauna of types 1 and 2: (ZNIEFF) describe mostsites of special heritage value. The zones of type 1 are sites, gener-ally covering a small area and characterised by the presence of spe-cies or habitat that are rare, remarkable or characteristic of thenational or regional natural heritage. Those of type 2 are great nat-ural formations (forest, valley, plateau, estuary) which possess animportant biological potential. They may include several zones oftype 1. The ZNIEFF has gradually became a useful management toolin France used in a number of procedures although it does not haveany direct legal significance.

The low valley of the Somme constitutes a vast meadow space,extremely flat, sometimes intersected with hedges. Water is omni-present there. The estuary and low valley areas are more and morevisited by tourists and are widely used for hunting. Nevertheless,its resources deserve to be taken into account for the benefits ofother users (farmers, walkers, naturalists...). Cattle farming consti-tute the principal economic activity and helps maintaining theopen character of this landscape. The area is classified as severalFrench ZNIEFFs.

European special areas for conservation (SACs) were designatedin the Seine by application of the Community directive of May 21,1992 (Habitat directive) concerning the conservation of naturalhabitats, wild fauna and flora. Other sites (285 on French territory)are of special value to one or several species of birds (listed inappendix 1 of the directive on Birds or migrating species, EEC 79/409, April 2, 1979). Both European directives constitute the basisfor the Natura Network 2000. The estuary and lower valley of theSomme are within a Natura 2000 site named ‘Picard Estuariesand Littoral’. They are also integrated into the Ramsar ‘Bay ofSomme’ site.

Several other small-protected wetland areas include land pur-chased by the Conservatoire des Espaces Littoraux et des RivagesLacustres (see Alard, 2002). They consist in biologically and envi-ronmentally valuable portions of land in the lower Seine and Rislevalleys, and coastal areas in the Somme. Between Abbeville and theestuary, the low valley of the Somme has both an interesting eco-logical richness and some landscape quality. Within the frameworkof an integrated strategy of space management, short-termimprovements were attempted on the land of the CLRL. Theseimprovements have tended to diversify habitats and to controlthe passage of public on natural areas.

Following the building of new harbour facilities, compensatoryactions were decided in order to preserve ecological functions inthe Seine estuary (Bessineton, 1988; Hamm et al., 2001; Dauvinet al., 2006). For Port 2000, when the French Authorities decidedto ratify the extension project for Le Havre harbour in September1998, they underlined the importance of striking a balance be-

tween the Port 2000 project’s economic development objectivesand the protection of aquatic habitats via a specific managementprogramme for the Seine estuary. The presumed effects of highcurrent velocities in the North Channel included: (i) an oscillatingwater volume that would lead to the silting up of the North Chan-nel itself, and (2) a loss of benthic fauna (Dauvin, 2002, 2006b). Inorder to minimize hydro-sedimentary and biological changes, andto preserve the ‘Grande Vasière’ tidal flat, located in the upper partof the North Channel, several compensatory actions were plannedbetween 2002 and 2006. These actions included (Fig. 5): (i) open-ing the North Dyke, upstream from the Normandy Bridge, anddredging of a channel connected to the North Channel; (ii) risingan existing opening to the level + 3.5 m in order to allow waterto flow more easily toward the new upstream opening; (iii) con-structing an immersed dyke supported by the North Dyke in orderto increase the circulation of seawater during ebb tide; (iv) prolon-gating the North Dyke 750 m in the direction of the sea; (v) dredg-ing more than 5 million tons of sediment; and (vi) constructingartificial roosting sites for birds, on the northern bank as well asin the South Channel (Dauvin et al., 2006). A questionnaire was cir-culated to citizens to test their knowledge of compensatory actionstaken after the construction of Port 2000 (Olivier Sirost, personalcommunication). Only 11% of the person polled knew at leastone compensatory action. The number of known compensatory ac-tions was 1.7/5. The main known action was the artificial roostingsites for birds which was also the more mediatised through TV andnewspapers.

Today a third crossing through the estuary is discussed, whilethe PAH has began a study to increase the Large Central Channeland the PAR has a project to dam up the river down to Rouen topermit large container ships to reach Rouen basins. There is alsoa project for 2010 to increase the size of fluvial boats upstreamfrom. Remaining islands would be under threat of destruction.What assessments can one use from the 25 last years to preventremaining wetlands becoming degraded especially that of theaquatic habitats.

5. Conservation and restoration experiences

In the Seine, important biotopes (see Olenin and Ducrotoy,2006, for a discussion of the definition of biotopes), such as mudflats have disappeared because of their natural or artificial (anthro-pogenic) filling, and other modifications of hydro-sedimentaryconditions. They include the construction of dykes and the dredg-ing of channels for navigation. The present geo-morphologic andbiological status of the estuary is perhaps best represented as se-ven distinct entities, or compartments, which underline the highdegree of compartmentalisation of the Seine estuary’s biologicalstructure, from upstream to downstream (Fig. 6). New restingplaces for birds are being constructed on artificial dunes or smallislands. In order to use and perennialise the remaining flats, ithas been necessary to restore favourable ecological conditions,such as former meanders. Few biotopes of the river course still ex-ist, as they were gradually disconnected from the minor coursesthrough hydraulic and biological processes. They mainly consistof wet meadows occupying old meanders of the Seine. Longitudi-nally, the damming up of the estuary caused a dislocation of thehydrosystem by limiting the expansion of communities. Firstly, adecrease in the biodiversity of macrozoobenthic species took placeat the mouth of the estuary (Dauvin et al., 2006) due to the effect ofincreased flushing and displacement of the limit of salinity. Sec-ondly, a parallel reduction of habitats favourable to fresh water fish(Dauvin, 2006b) was observed. They are now confined upstream ofRouen. In the nature reserve, the rehabilitation of degraded sys-tems required a modification of practices. The port authorities, at

Fig. 5. Compensatory actions planned in the Seine estuary (from Dauvin et al., 2006).

Fig. 6. Map of the principal compartments composing the Seine estuary’s biological structure (from Dauvin, 2006b) – (1) Lower part of the navigational channel. (2) Upperpart of the navigational channel. (3) South Channel. (4) North Channel. (5) Estuary mouth. (6) Wetlands and salt marshes. (7) Developed zones on the periphery of thewetlands, including the industrial/port district.


the beginning of the 2000s, set up schedules of conditions on hunt-ing and the exploitation of reeds. This avoided further degradation.Measures used included: banning a change to permanent mead-ows, limitating loads of pasture, using manure, pesticides, control-ling dates for mowing and managing water levels. Measures of thiskind should be put in action at a broader scale on the major bed be-

cause the study of estuarine fish has yielded essential informationdemonstrating acute ecological problems. On the one hand, be-cause of the impoverishment of fresh-water communities, a moreor less complete rupture of biological cycles (pike, but also cyprin-idaes) has been taking place. On the another hand, the diverse con-struction and development projects provided many obstacles for


the upstream–downstream passage of the large migratory diadro-mous species, such as salmon (Salmo salar), sea trout (Salmo trutta),allis shad (Alosa alosa), twaite shad (Alosa fallax), fluvial (Lampetrafluviatilis) and sea lamprey (Petromyzon marinus), and sturgeon(Acipenser sturio) (Dauvin, 2006b). In the marine part of the estu-ary, a drastic reduction in its function as a nursery has affectedpopulations of sea bass (Dicentrarchus labrax), flounder (Platichthysflesus), eel (Anguilla anguilla), sole (Solea vulgaris) and the brownshrimp (Crangon crangon) (Dauvin, 2006b).

In the Somme valley, actions carried out within the frameworkof the local management plan 1998–2002 (1st phase) of the Nat-ure Reserve helped in maintaining the ecological diversity whilecontributing to the improvement of selected polders throughflooding. Small flood banks and water regulation systems wereset up with the aim to store water in two areas at Blanquetaque(Fig. 3). After two years, the flooded zones fulfilled their role fornight feeding of ducks. In the second phase (after 2002), the pro-ject aimed to at improve water retention, while making the limitsof the site more watertight by integrating hydraulic systems andreinforcing dykes. Former polders were connected to each otherto broaden and increase the depth of drainage ditches, used incase of overflooding. Other constructions included the erectionof a visual screen, made of products from the digging of the chan-nels. Overall, engineering work contributed to controlling waterlevels to improve the state of the communal byway, now accessi-ble to bird watchers in periods of flood. Population control of saltmarsh plants (Spartina spp.) has been carried out. Spartina is a pio-neer plant, which is often accompanied by Salicornia spp. It colo-nizes the highest parts of mud flats. The expansion of thisgraminaceous plant can have notable consequences on the estua-rine ecosystem. The density and the solidity of its rhizomes makethis plant’s colonization not easily reversible. Its leaves are drawnup facing the current and can trap organic remains and sediments.So, it can contribute to the plugging of estuaries. In order to decideon the best way of controlling the progression of Spartina, exper-iments in local eradication were undertaken in the late 1990s. Aprotocol (unpublished) was then written thanks to the participa-tion of scientists from several disciplines in order to attempt tocontrol the plant over large areas. The operation was claimednot to aim to ‘eradicate’ the plant from the Bay of Somme, butrather would intend ecological safeguarding. The awaited resultwas the conservation of unvegetated habitats in which inverte-brates were able to develop, allowing species of wading birds tofeed during a part of their annual cycle. The area affected by theinterventions covered about thirty hectares, including sectorsslightly colonized. The control of Spartina was carried out by suc-cessive passages of a tractor equipped with a rotary cultivator inperiod of neap tides. The farm equipment is acquired thanks tofinancial assistance from the local government.

At the beginning of the 1960s, in order to fight against thestranding of the access channel to the harbour of le Crotoy, thecourse of the Dien River was diverted in a channel skirting the har-bour. Because of low water volumes, the effectiveness of the strat-egy remained very modest. Today, the old course of Dien is stillvisible on the ground (Fig. 4). The objectives of the current projectare to re-use the sluice gates located under the dam, to restore theold river bed, and to rehabilitate several tens of hectares of pasture.In the mid-term, it is expected to facilitate collecting run-off, dur-ing periods of heavy rainfall. At the economic level, it is hoped tohelp restore an area used by sheep and to facilitate the traffic inthe Bay. The landscape would also be enhanced by diversifyingthe vegetation. Phases of maintenance and management of there-estuarisation of the Dien River will be accompanied by the insti-gation of a multiple partnerships between communes, local finan-cial syndicates, hunting organisations and various bodiesrepresenting the state.

6. Towards a strategy for restoring damaged estuarine habitats

6.1. Restoration as part of an integrated approach to coastalmanagement

Examining the above examples will help to set up an agendafor the restoration of damaged estuarine habitats. The are no com-prehensive approaches in any of both estuaries as an holistic viewis missing and there was no assessments of impacts at the estuaryscale. The reconnection of damaged habitats appeared as the onlyway towards re-estuarisation. Longitudinally, the building ofdykes had dislocated hydro systems and limited access to estua-rine communities. Such constructions led to an increase of tidaleffects and salinity, which forced estuarine species out of the estu-aries. Transversally, dykes broke connections between aquatichabitats and reduced the area and diversity of marshes. In parallel,the decline of fresh water areas meant that habitats had been lostfor fish.

Restoration work and compensation after engineering work hastaken place in both estuaries. In both cases, the intention was pre-serving or rehabilitating ‘natural’ features into the ecosystems.However, the redevelopment of isolated aquatic systems mightcontribute to further patchiness in the main estuarine ecosystemsas seen in the Somme with the building of new dykes and channels.This will increase the compartmentalisation of the area. It wouldseem that both in the Seine and in the Somme, objectives of resto-ration were unclear. In some cases, they target biodiversity, in oth-ers, particular species or communities (very often birds). Apluridisciplinary approach to outline objectives and methodsshould have been used because restoration objectives should focuson ecosystem functioning rather than structure description. Themultiplication of stakeholders complicated the management ofthe estuaries and decision-making because of divergent interestsand sometimes even opposition. For instance, the work on theproperties of the CELRL in the Somme was mostly intended tomanage tourist fluxes using communal byways. With this inten-tion, managers and scientists should have adopted an integratedapproach to management, and worked together towards agreedobjectives. Interactions to be taken into account are to be under-stood in terms of morphology, sedimentology and chemistry (sil-ting, transportation, erosion, adsorption, and oxidation areas. . . –sinks and source) and human activities. Those, such as tourism,should have been considered as integrated into the ecosystemand not just to be treated independently (Crossland et al., 2005).

Today, it appears indisputable that estuarine wetlands andaquatic environments are at risk in the Seine and also in theSomme, even when managed by those with good intentions. Inter-tidal zones are the most vulnerable due to various existing andplanned constructions in the estuaries. The priority to restore themmust be recognized and must be the subject of a true consensus inthe framework of an ecosystemic and interdisciplinary approach.Recent studies (Dauvin, 2006a,b; Dauvin et al., 2006) in the Seineestuary showed that essential functionalities were still operating,but were more or less degraded and/or reduced in intensity. Thetop priority is the re-establishment of these functional connectionsfrom the hydrological and biological point of view between theland of the Nature Reserves to the North of the alluvial plain andthe river axis located in the South, as well as the improvement offresh water in particular in and between the meanders. Withinthe framework of the management plan of the Nature Reserve, fourspecific operations are currently programmed in the Seine estuary:(i) the study of the hydraulic operation of the sector of the MarePlate; (ii) a survey of water levels (artificial ponds, reed beds,meadows, resting places for birds, dunes); (iii) an assessment ofhydraulics, and (iv) restoration of North–South fluxes in the wetmeadows.


In a context of improvement of water quality for the last 20years, the real problem has not been the transit of large migratingfish but the functioning of populations, which depend more onthe estuary. Any estuary would keep its essential function as anursery and reproduction site of a targeted species only if thereis a persistent association with the various water masses andthe related wetlands. The following orientations could be takenin both estuaries: the reconnection of hydraulic unit, targetingthe return of pike (Esox lucius), the rehabilitation of wet mead-ows. The re-establishment of freedom of movement should alsobe considered on the small tributary rivers to the Seine and theSomme. They have a potential in term of zones of spawninggrounds for the fluvial lamprey (Lampetra fluviatilus). The Euro-pean eel is present in the higher parts of estuaries and reachthese tributaries. Technical and administrative support on thesectors concerned is needed.

6.2. Need for a global restoration plan

The above examples demonstrate that any construction projectshould be incorporated into a global restoration plan, working onthe long-term. An ecological vision for the long-term would meananalyzing the past to predict the future and promoting local activ-ities in harmony with estuarine conditions. Such an approachwould lead, in the mid-term (10–20 years), to typical estuarinecommunities coming back. In the short-term (a few years), reducedscale re-estuarisation (depolarisation experiments on demo-sitesfor instance) would be useful for experimenting and acquiring fullcompetence in ecological engineering for restoring damaged habi-tats. Acquiring technical skills (ecological engineering) would al-low launching full scale pilots adapted to local conditions andusing new protocols. After scientific selection of sites in relationto water quality, salinity and pollutants fluxes, these experimentscould be used as demonstrations and tests on restorationprocedures.

Based on reconstruction of paleoenvironmental variations andhistory, scenarios could be proposed on the long-term (50 years)as a virtual image of a possible future estuary (‘utopian perspec-tive’). The sociological aspect of this should not be underestimatedas the plan could serve as a potential communication tool. Themaster plan would result from cross-linkages of data from a GISthat would be supplied with relevant data. The fundamental prin-ciple behind this is increasing the volume of water entering theestuary to include the valley as well as the limiting hills or cliffs.The following protocol should be applied in the short run to buildthe project of restoration:

� Analyse past experience: which main ideas function and whichare the causes of failure? Identify key elements to break thedynamics of the partitioning (always in progress) of the estuary.

� Improve projects with environmental vocation (new meanderor restore water connections).

� Anticipate the future with an ambitious project of restoration ofthe aquatic environments and wetlands at several scales.

In all cases, the restoration projects would require financial sup-port on the long term.

Four scenarios, corresponding to four key strategic questions,were studied in 2005 under the aegis of the Seine Estuary Coun-cil (Dauvin, 2006a): What would be the consequence for environ-mental functions if present trends continue? Can environmentalfunctions be restored to their 1980 level and under what condi-tions? What conditions will lead to a catastrophic scenario, andwhat would be its consequences? What are the financial limitsof such projects? This forecast study had three principle effects.It increased comprehension of the estuarine system functions

by the local stakeholders, established a shared vision of futurepossibilities for the environmental functions of the estuary by2025, and underlined the need to continue collaborative effortsin the spirit of ICZM. Monitoring the implementation of the pro-ject would allow adaptive management and a progressive resto-ration of environmental functions. In the second step of theprocess, the study will be continued (2006–2007) to determinethe monetary cost of two of the four scenarios, the second andthe fourth.

7. Discussion

In this paper, the Seine and the Somme estuaries (North-Wes-tern France) were considered as zones of transition where riversdischarge into the sea. Interfaces between fresh and marine watersand the atmosphere are very important there. Ecosystems thatfunction as eco-tones are usually closely connected to the ecosys-tems adjacent to them and are characterised by a rapid flux ofmaterials and organisms (Ewel et al., 2001). Such ecotones playvarious roles, influencing water flows, accumulating sedimentsand organic matter, processing nutrients, and providing opportuni-ties for recreation. Both systems located along the French coast ofthe English Channel show a high import of sediments from the sea.In addition, they have been the focus of intensive human activitieswhich have accelerated the plugging of estuarine systems andthreatened continuity between ecological functional units. There-fore, there was a considerable reduction of the intertidal zone inboth estuaries, concurrently with an increase of vegetated surfacescolonised by reed beds (Seine) or Spartina (Somme). Both estuaries,considered in relation to their watersheds, are critically importantzones but their preservation and protection is not sufficient. Diffi-culties in implementing ecological qualitative objectives often liein the lack of rigour in the terminology and the lack of respect ofecological concepts (Olenin and Ducrotoy, 2006). However, estuar-ies are well delimited ecosystems, at least upstream, and humanimpacts are often well understood. Here, in the proposed casestudies, the Seine is considered as heavily industrialised, whereasthe Somme looks much more ‘natural’. In both systems, after morethan one century and a half of degradation of estuarine habitats,environmental awareness has increased under the pressure of sci-entists to restore their functionalities. At first, the goal of restora-tion was defined as the need to conserve diversity. Thedevelopment of biodiversity surrogates at small scales (i.e. habitatsand biotypes) has had an increasingly important role in the identi-fication of sites that could contribute to the re-establishment oftypical communities (Banks and Skilleter, 2002; Olenin and Ducro-toy, 2006) both in the Seine and in the Somme. However, restoringan ecosystem consists not only in restoring attributes lost by thisecosystem, but also in replacing selected functions with anotherecosystem which will fulfil the functions required. Functions arecarried out thanks to a certain number of processes (or operations)in which living organisms play a role, through their interactions.Fundamentally, ecosystems will:

(i) Transfer energy, and thus be organized in trophic networks.(ii) Be composed of habitats or biotopes which can shelter a

diversity of species (complexity, heterogeneity).(iii) Develop and evolve.(iv) Interact with adjacent ecosystems.

The significance of biodiversity in marine sediments to ecosys-tem functions is still poorly understood, but individual species andfunctional groups are known to carry out activities that have globalimportance. It is known that macrofaunal activity impacts globalcarbon, nitrogen and sulphur cycling, transport, burial and metab-


olism of pollutants, secondary production including its impact oncommercial species, and the transport of sediments (Snelgrove,1998). Bolam et al. (2002) have challenged this point of view. Theysupported the null hypotheses of no relationship between ecosys-tem functions and attributes such as diversity and biomass. Itshould be noted that their experiments were limited in both spatialand temporal scale; the implications of this when scaling up to lar-ger scale generalizations are doubtful. Anyway, it cannot be deniedthat relations between biological diversity and ecosystem func-tions in estuaries are very complex and may depend more on func-tional groups than species richness. Changes in the structure ofsedimentary benthic assemblages, especially in relation to anthro-pogenic perturbations, are based on the recognition of ecologicalgroups of different sensitivity to pollution (Pearson and Rosenberg,1978).

In the Somme and the Seine, further field experiments areneeded and should be part of any future restoration strategy aswell as a methodology to determine the species to be targeted inorder to be able to assess the changing ecological quality of the sys-tems considered. From the Seine example, it appears that it couldbe wrong to reconnect habitats as they would be likely to be con-taminated by chemicals trapped in the sediments. The index ofcondition of the cockle (Cerastoderma edule) in the Seine estuaryis approximately 2 times lower than that of the Somme; thegrowth rate of young plaice (Pleuronectes platessa) is weak that ofthe bass (Dicentrarchus labrax) is lower in the Seine than in theLoire. The feminization of 10% of males of flounder (Platycthys fle-sus) has certainly had an effect on the population dynamics of thespecies.

Rigorous monitoring programs, which depend upon the rele-vant choice of indicators (Dauvin et al., 2008), are required.Geographical delimitation and description of the ecosystem con-sidered (data bases, GIS...) is necessary as the management andsustainable use of the natural resources may be improved as a re-sult of accurate habitat mapping (Sheppard et al., 1995; Olenin andDucrotoy, 2006). It would be beneficial to review trends in theestuaries, with effects and side effects of recent restoration mea-sures. In the Seine, it would be advisable to survey fish populationsas indicators of change. From the Somme example, we have seenthat the concepts of conservation and restoration might diverge.It is indeed possible to safeguard the presence of one or severalspecies (often charismatic such as birds) which raise concern whilethey remain on limit of survival threshold levels. Restoration sup-poses a higher level of intervention through which one seeks to in-crease the abundance of these populations. The quality andquantity of the habitat are obviously crucial and are connectedand therefore they must be considered together, that is, they haveto exist in sufficient quantity and be of good quality. In the Sommearea, the construction of new dykes and channels may be workingagainst particular interactions, such as the mixing of chemicals andsediments. In a more general way, the restoration of habitats andfunctions requires a very broad pluridisciplinary reflexion on thelevel of definition of objectives as well as of methods (Ducrotoyand Elliott, 2006). This is why defining various potential trajecto-ries and confronting them with results of fedd-back monitoring,in the local and regional context (biological and human) wouldhelp to achieve the decompartimentation of the estuary from bio-tope to landscape level.

The lack of management plans is a key issue in both the stud-ied estuaries. It is strongly recommended that such plans be putin place in all European estuaries and that guidelines be pub-lished to build them. While legal obligations under European Un-ion Nature and European EIA law will surely continue to have abearing on future management, Integrated Costal Zone Manage-ment is not legally binding and is more considered here as a gen-eral approach to coastal management. What is lacking is a

template for estuarine management plans, applicable throughoutEurope.

Efficient procedures of socio-ecological evaluation of habitatsare an essential tool for tracking changes in habitat quality andin adjudicating environmental mitigation. All current methodsfor estimating habitat values of coastal marine sites rely heavilyon the opinion of experts or on data variables that can readily bemanipulated to influence the outcome. As a result, unbiased, quan-titative comparisons between the values of different marine habi-tats are generally unavailable (Bond et al., 1999). Robust andobjective techniques for the valuation of habitats could help tomodify selected trajectories, in response to socio-economicrequirements. In this spirit, ‘feed-back monitoring’ would possiblylead to suitable reorientations of a global restoration plan. This iswhy a good understanding of adaptive management strategies isneeded to establish a dialogue with managers and stakeholderson technical and management issues. A vision of the estuary onthe mid-term (20 years) and long-term (50 years) would undoubt-edly lead to successful restoration. There is considerable opportu-nity for fruitful collaborations between scientists, localcommunities and managers in the spirit of ICZM (Yanagi andDucrotoy, 2003).

Acknowledgements

This study was undertaken as part of the Seine-Aval Pro-gramme, which was coordinated by the GIP Seine-Aval. The PICCELprogramme was funded by the Picardy Region and the Departmentof the Somme. The authors thank all the participants of the Resto-ration Working Group of Seine-Aval for very useful discussions,which are expressed in this paper, Thierry Ruellet for the figuresand two anonymous referees for their very useful comments onthe first draft of this paper.

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