199
physicochemical regulator for numerous natural
chemical species as well as pollutants, notably
metals. But, due to the tide, there is no anoxic zone
in the downstream estuary (Guézennec et al. 1999 ).
The Seine valley is of major economic importance for France, notably due to the presence of
two maritime harbours, Rouen and Le Havre.
The Seine estuary lies at the discharge point of a
catchment’s area covering 78,000 km
2 . This area
is inhabited by 16 million people (>25 % of the
French population, with Paris the French capital
and two major cities, Rouen and Le Havre) and
accounts for 50 % of the river traffi c in France,
40 % of the country’s economic activity and
30 % of the agricultural activities.
Anthropogenic infl uences in the Seine estuary
began during the early mid nineteenth century
and continue up to the present day (Guézennec
et al. 1999 ; Dauvin 2006 , 2009 ; Fisson 2014 ).
The estuary’s ecosystems became more fragile as
a result of cumulative human activities, mainly
due to harbour and industrial development
(dredging and disposal of sediment dredged from
the harbours, embankment works and construction of dykes and creation of industrial development areas). These activities have led to the
extreme compartmentalisation of the units, a
reduction of the intertidal zone (loss of more than
100 km
2 between 1850 and the present day), the
downstream migration of the maximal turbidity
zone and the increase of muddy deposits in the
subtidal areas of the Bay of Seine (Guézennec
et al. 1999 ). At the same time, the physicochemical conditions of the estuarine environment have
continually deteriorated over more than a century.
By the 1980s, the estuary had become highly
contaminated: levels of metal pollutants (e.g.
Cd, Hg), hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were among the highest
recorded worldwide. Moreover, insuffi cient or
inadequate water treatment facilities created an
oxygen defi cit downstream of Paris and Rouen
(Abarnou et al. 2000 ; Fisson 2014 ). In the marine
estuary, abnormal biological functioning led to
the collapse of the fi sheries sector, particularly in
the case of the brown shrimp Crangon (declining
from 1,000 t in 1970s to < 100 t since the beginning of the 1990s), while, in the fl uvial estuary,
professional fi shing ceased entirely in the 1970s
due to the almost total disappearance of migratory
fi sh species (Dauvin 2002 ). Nevertheless, we can
nowadays observe a signifi cant decrease in metal
contamination, an improvement in oxygenation
and a reduction of the phosphorus and ammonia
fl uxes (Fisson 2014 ). Despite this, some chemical
contaminants persist such as PAHs, PCBs and
pesticides, while new questions are arising on
emerging contaminants such as phthalates and
medicinal residues (Fisson 2014 ).
2.2
Multiple Perceptions
of the Seine Estuary
Because estuaries have no true specifi c legal
status, there are multiple perceptions of the
continuum between the estuary and the Bay of
Seine. Hence, the Seine estuary is characterised
in many different ways (Desroy et al. 2004 ;
Dauvin and Ruellet 2009 ): for geographers and
physicists, the estuary extends from Poses to the
sea, while biologists distinguish several zones
according to the salinity (ranging from the freshwater zone to oligo-, meso-, poly- and fi nally
euhaline zones ); three transitional water bodies
are defi ned by the Seine-Normandy Water
Agency for the implementation of the Water
Framework Directive; the Territorial Directive
Plan for the French government takes into
account a wide area including a large part of
Lower Normandy and the Seine valley. This area
covers a very extensive territory including the
Paris region and a large part of historical
Normandy from Dieppe in the east to Cherbourg
in the west. In the communes bordering the Seine
estuary, the association of elected offi cials only
considers the lower part of the estuary. On the
other hand, the Upper Normandy Regional
Council (Rouen), like the geographers and the
French government, considers that the estuary
extends up to Poses. Estuary managers are interested in the part of the estuary that borders their
The Estuary-Bay of Seine Continuum: The Need for an Ecosystem-Based Management
physicochemical regulator for numerous natural
chemical species as well as pollutants, notably
metals. But, due to the tide, there is no anoxic zone
in the downstream estuary (Guézennec et al. 1999 ).
The Seine valley is of major economic importance for France, notably due to the presence of
two maritime harbours, Rouen and Le Havre.
The Seine estuary lies at the discharge point of a
catchment’s area covering 78,000 km
2 . This area
is inhabited by 16 million people (>25 % of the
French population, with Paris the French capital
and two major cities, Rouen and Le Havre) and
accounts for 50 % of the river traffi c in France,
40 % of the country’s economic activity and
30 % of the agricultural activities.
Anthropogenic infl uences in the Seine estuary
began during the early mid nineteenth century
and continue up to the present day (Guézennec
et al. 1999 ; Dauvin 2006 , 2009 ; Fisson 2014 ).
The estuary’s ecosystems became more fragile as
a result of cumulative human activities, mainly
due to harbour and industrial development
(dredging and disposal of sediment dredged from
the harbours, embankment works and construction of dykes and creation of industrial development areas). These activities have led to the
extreme compartmentalisation of the units, a
reduction of the intertidal zone (loss of more than
100 km
2 between 1850 and the present day), the
downstream migration of the maximal turbidity
zone and the increase of muddy deposits in the
subtidal areas of the Bay of Seine (Guézennec
et al. 1999 ). At the same time, the physicochemical conditions of the estuarine environment have
continually deteriorated over more than a century.
By the 1980s, the estuary had become highly
contaminated: levels of metal pollutants (e.g.
Cd, Hg), hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were among the highest
recorded worldwide. Moreover, insuffi cient or
inadequate water treatment facilities created an
oxygen defi cit downstream of Paris and Rouen
(Abarnou et al. 2000 ; Fisson 2014 ). In the marine
estuary, abnormal biological functioning led to
the collapse of the fi sheries sector, particularly in
the case of the brown shrimp Crangon (declining
from 1,000 t in 1970s to < 100 t since the beginning of the 1990s), while, in the fl uvial estuary,
professional fi shing ceased entirely in the 1970s
due to the almost total disappearance of migratory
fi sh species (Dauvin 2002 ). Nevertheless, we can
nowadays observe a signifi cant decrease in metal
contamination, an improvement in oxygenation
and a reduction of the phosphorus and ammonia
fl uxes (Fisson 2014 ). Despite this, some chemical
contaminants persist such as PAHs, PCBs and
pesticides, while new questions are arising on
emerging contaminants such as phthalates and
medicinal residues (Fisson 2014 ).
2.2
Multiple Perceptions
of the Seine Estuary
Because estuaries have no true specifi c legal
status, there are multiple perceptions of the
continuum between the estuary and the Bay of
Seine. Hence, the Seine estuary is characterised
in many different ways (Desroy et al. 2004 ;
Dauvin and Ruellet 2009 ): for geographers and
physicists, the estuary extends from Poses to the
sea, while biologists distinguish several zones
according to the salinity (ranging from the freshwater zone to oligo-, meso-, poly- and fi nally
euhaline zones ); three transitional water bodies
are defi ned by the Seine-Normandy Water
Agency for the implementation of the Water
Framework Directive; the Territorial Directive
Plan for the French government takes into
account a wide area including a large part of
Lower Normandy and the Seine valley. This area
covers a very extensive territory including the
Paris region and a large part of historical
Normandy from Dieppe in the east to Cherbourg
in the west. In the communes bordering the Seine
estuary, the association of elected offi cials only
considers the lower part of the estuary. On the
other hand, the Upper Normandy Regional
Council (Rouen), like the geographers and the
French government, considers that the estuary
extends up to Poses. Estuary managers are interested in the part of the estuary that borders their
The Estuary-Bay of Seine Continuum: The Need for an Ecosystem-Based Management