5 Further Improvement of Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
5.1 Progress Made in Wastewater Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
5.2 Acting on Diffuse Agricultural Sources to Improve Water Quality . . . . . . . . . . . . . . . . . 207
5.3 Impact of the Seine River Nutrient Fluxes at the Coastal Zone . . . . . . . . . . . . . . . . . . . . . . 208
5.4 The Context of Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
6 Conclusions and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Abstract At the start of the PIREN-Seine program, organic pollution by the effluent
of the Parisian conurbation was responsible for episodic anoxia in the lower Seine
River, while nutrients from both point and diffuse sources are used to cause
eutrophication, a nuisance for drinking water production from surface water and
biodiversity. The implementation of the EU Water Framework Directive led to a
drastic decrease of organic carbon, phosphorus and ammonium concentrations in
surface waters starting in the early 2000s and to a reduction of the frequency and the
amplitude of phytoplankton blooms. However, nitrate contamination from fertiliserintensive agriculture continued to increase or at best levelled off, threatening
groundwater resources and causing unbalanced nutrient ratios at the coastal zone
where eutrophication still results in harmful algal blooms. High-frequency O 2 data
combined with models, which have been developed for 30 years, can help discriminate the contribution of auto- vs. heterotrophic metabolism in the CO 2 supersaturation observed in the Seine River. Despite the impressive improvement in water
quality of the Seine River, episodic crises such as summer low-flow conditions
still threaten the good ecological status of both river and coastal waters. Modelling
scenarios, including further wastewater treatments and structural changes in agriculture and future changes in hydrology under climate changes, provide the basis for a
future vision of the ecological functioning of the Seine River network.
Keywords Aquatic continuum, Ecological functioning, Long-term socioecological
study, Riverstrahler model, Scenarios
1 Introduction
The concept of ecosystem functioning lies at the root of ecological sciences
[1, 2]. It was at the origin of the International Biological Program, which coordinated
large-scale ecological and environmental studies during the 1964–1974 period.
Regarding aquatic ecosystems, the first research efforts were devoted to stagnant
systems (lakes, sandpit lakes, reservoirs) where discharged point sources (domestic
and industrial) were recognised as a major cause of water quality alteration through
eutrophication and organic pollution. Many comprehensive studies started at that
time, showing, based on long-term whole-ecosystem experiments, the strict control
of primary production by phosphorus [3, 4], while silica (Si) depletion occurring
190
J. Garnier et al.
5.1 Progress Made in Wastewater Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
5.2 Acting on Diffuse Agricultural Sources to Improve Water Quality . . . . . . . . . . . . . . . . . 207
5.3 Impact of the Seine River Nutrient Fluxes at the Coastal Zone . . . . . . . . . . . . . . . . . . . . . . 208
5.4 The Context of Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
6 Conclusions and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Abstract At the start of the PIREN-Seine program, organic pollution by the effluent
of the Parisian conurbation was responsible for episodic anoxia in the lower Seine
River, while nutrients from both point and diffuse sources are used to cause
eutrophication, a nuisance for drinking water production from surface water and
biodiversity. The implementation of the EU Water Framework Directive led to a
drastic decrease of organic carbon, phosphorus and ammonium concentrations in
surface waters starting in the early 2000s and to a reduction of the frequency and the
amplitude of phytoplankton blooms. However, nitrate contamination from fertiliserintensive agriculture continued to increase or at best levelled off, threatening
groundwater resources and causing unbalanced nutrient ratios at the coastal zone
where eutrophication still results in harmful algal blooms. High-frequency O 2 data
combined with models, which have been developed for 30 years, can help discriminate the contribution of auto- vs. heterotrophic metabolism in the CO 2 supersaturation observed in the Seine River. Despite the impressive improvement in water
quality of the Seine River, episodic crises such as summer low-flow conditions
still threaten the good ecological status of both river and coastal waters. Modelling
scenarios, including further wastewater treatments and structural changes in agriculture and future changes in hydrology under climate changes, provide the basis for a
future vision of the ecological functioning of the Seine River network.
Keywords Aquatic continuum, Ecological functioning, Long-term socioecological
study, Riverstrahler model, Scenarios
1 Introduction
The concept of ecosystem functioning lies at the root of ecological sciences
[1, 2]. It was at the origin of the International Biological Program, which coordinated
large-scale ecological and environmental studies during the 1964–1974 period.
Regarding aquatic ecosystems, the first research efforts were devoted to stagnant
systems (lakes, sandpit lakes, reservoirs) where discharged point sources (domestic
and industrial) were recognised as a major cause of water quality alteration through
eutrophication and organic pollution. Many comprehensive studies started at that
time, showing, based on long-term whole-ecosystem experiments, the strict control
of primary production by phosphorus [3, 4], while silica (Si) depletion occurring
190
J. Garnier et al.