(pressures/driver). Another indicator of environmental pressure, rated to the basin
population, is the per capita excess load (Fig. 1, Steps I and J), i.e. the excess flux
divided by the basin’s population upstream of the coring station (ELcap), expressed
in g cap
À1 year
À1 . Both indicators can be used to compare the efficiency of
environmental regulations in river basins and their trajectories, provided that past
metal contents are reconstructed on the basis of dated sediment archives and past
metal demands are recovered by an analysis of the area’s economic history
[25, 35, 36].
3 The Seine River Basin and Its Contamination
by Micropollutants
The Seine River basin has one of the highest ratios of pressures to river sediment
fluxes, which results in a very high contamination level in the lower Seine River,
downstream of Paris. This contamination by metals and by numerous organic
pollutants was not assessed before 2006 when new monitoring strategies were
applied, following the EU Water Framework Directive (WFD). At that time, the
first cores taken in the Seine River basin revealed the unknown long-term history of
contamination, which reached very severe levels, when compared to current sediment quality guidelines.
3.1 The Seine River Basin: A Sensitive Territory Under High
Pressures
In addition to the pressures (e.g. climate, morphology, land use, etc.) described
earlier in this volume [37], the basin is characterised by a highly biased population
distribution: about 70% of the basin’s population is concentrated in the Paris
megacity (2,750 km
2 with ten million inhabitants), which covers only 4% of the
basin area. The upper Seine River and Marne tributary meet at Paris (Fig. 1 [37]),
and the lower Seine River receives the other main tributary, the Oise River, downstream of the Paris megacity. The Paris megacity’s main wastewater treatment plant
(WWTP) at Achères, today called “Seine-Aval”, discharges the treated effluent just
upstream of the Seine-Oise confluence, some 70 river km downstream of the centre
of Paris. Its capacity gradually grew in three decades to 8 M people at the end of the
1980s and then decreased to 6.5 M people because of the construction of additional
WWTPs, which still makes it the largest WWTP in Europe.
The lower Seine River is structurally very sensitive to wastewater inputs, due to
its minimal sediment transport and, above all, to its limited summer dilution during
low flows (110 m
3 s
À1 ).
276
S. Ayrault et al.
population, is the per capita excess load (Fig. 1, Steps I and J), i.e. the excess flux
divided by the basin’s population upstream of the coring station (ELcap), expressed
in g cap
À1 year
À1 . Both indicators can be used to compare the efficiency of
environmental regulations in river basins and their trajectories, provided that past
metal contents are reconstructed on the basis of dated sediment archives and past
metal demands are recovered by an analysis of the area’s economic history
[25, 35, 36].
3 The Seine River Basin and Its Contamination
by Micropollutants
The Seine River basin has one of the highest ratios of pressures to river sediment
fluxes, which results in a very high contamination level in the lower Seine River,
downstream of Paris. This contamination by metals and by numerous organic
pollutants was not assessed before 2006 when new monitoring strategies were
applied, following the EU Water Framework Directive (WFD). At that time, the
first cores taken in the Seine River basin revealed the unknown long-term history of
contamination, which reached very severe levels, when compared to current sediment quality guidelines.
3.1 The Seine River Basin: A Sensitive Territory Under High
Pressures
In addition to the pressures (e.g. climate, morphology, land use, etc.) described
earlier in this volume [37], the basin is characterised by a highly biased population
distribution: about 70% of the basin’s population is concentrated in the Paris
megacity (2,750 km
2 with ten million inhabitants), which covers only 4% of the
basin area. The upper Seine River and Marne tributary meet at Paris (Fig. 1 [37]),
and the lower Seine River receives the other main tributary, the Oise River, downstream of the Paris megacity. The Paris megacity’s main wastewater treatment plant
(WWTP) at Achères, today called “Seine-Aval”, discharges the treated effluent just
upstream of the Seine-Oise confluence, some 70 river km downstream of the centre
of Paris. Its capacity gradually grew in three decades to 8 M people at the end of the
1980s and then decreased to 6.5 M people because of the construction of additional
WWTPs, which still makes it the largest WWTP in Europe.
The lower Seine River is structurally very sensitive to wastewater inputs, due to
its minimal sediment transport and, above all, to its limited summer dilution during
low flows (110 m
3 s
À1 ).
276
S. Ayrault et al.