5 Further Improvement of Water Quality
5.1 Progress Made in Wastewater Treatments
Riverstrahler is now used to explore various future wastewater treatment scenarios.
Although considerable improvements have been made in the largest WWTPs of the
Seine basin, some of the smallest WWTPs of the 1900 spread over the basin still
have to implement the Urban Wastewater Directives [64]. Compared to a reference
situation (2002–2014), nitrogen and phosphorus fluxes at the outlet of the Seine
River could be decreased by 10 and 20%, respectively, when current regulations of
tertiary treatments (nitrification and denitrification and dephosphatation) are generalised. For silica, a diffuse source pollutant, no visible change would occur with
further wastewater treatment (Fig. 9a). An appreciation of these efforts is provided
by a backward scenario simulating the situation of wastewater treatment as it was in
the 1980s. The difference with the reference scenario is very telling in terms of the
distance covered over the last 30 years. These results also indicate that any relaxation
in the treatment of domestic effluents, e.g. following a disengagement of the national
government, could lead to a dramatic situation. Slight changes in silica fluxes
(Fig. 9a) result from silica consumption with more or less nutrient (N, P) availability
for diatom growth.
Despite all the efforts made in WWTPs, which strongly improved the water
quality in the Seine River, nutrient fluxes delivered at the coastal zone are still
responsible for eutrophication in the Seine Bight, with toxic algal blooms [82] and
fishery problems. Moreover, nitrate contamination of groundwater [58] and closure
of drinking water wells are a real problem for the basin’s water agencies and drinking
water suppliers. Pesticide contamination, associated with intensive agricultural
practices, is also an important concern in the basin [83].
5.2 Acting on Diffuse Agricultural Sources to Improve Water
Quality
Point source pollutions are today almost completely under control. Simultaneously,
diffuse agricultural sources, particularly of nitrogen, have become the subject of
particular concern because of their cascading effect on many compartments of the
environment [84]. Two contrasted scenarios of the future of the agro-food system
have been established and compared [85, 86]. The first one consists of the continuation of the current trends of opening and specialisation (O/S) of the conventional
cropping systems following regulation but without questioning the basic structural
features of the current production system. The second scenario (A/R/D) involves a
radical reorganisation of agricultural production, generalising organic farming practices, reconnecting livestock and crop farming [57, 87] and changing human consumption towards a Demitarian diet, i.e. cutting consumption of animal proteins by
Ecological Functioning of the Seine River: From Long-Term Modelling. . .
207
5.1 Progress Made in Wastewater Treatments
Riverstrahler is now used to explore various future wastewater treatment scenarios.
Although considerable improvements have been made in the largest WWTPs of the
Seine basin, some of the smallest WWTPs of the 1900 spread over the basin still
have to implement the Urban Wastewater Directives [64]. Compared to a reference
situation (2002–2014), nitrogen and phosphorus fluxes at the outlet of the Seine
River could be decreased by 10 and 20%, respectively, when current regulations of
tertiary treatments (nitrification and denitrification and dephosphatation) are generalised. For silica, a diffuse source pollutant, no visible change would occur with
further wastewater treatment (Fig. 9a). An appreciation of these efforts is provided
by a backward scenario simulating the situation of wastewater treatment as it was in
the 1980s. The difference with the reference scenario is very telling in terms of the
distance covered over the last 30 years. These results also indicate that any relaxation
in the treatment of domestic effluents, e.g. following a disengagement of the national
government, could lead to a dramatic situation. Slight changes in silica fluxes
(Fig. 9a) result from silica consumption with more or less nutrient (N, P) availability
for diatom growth.
Despite all the efforts made in WWTPs, which strongly improved the water
quality in the Seine River, nutrient fluxes delivered at the coastal zone are still
responsible for eutrophication in the Seine Bight, with toxic algal blooms [82] and
fishery problems. Moreover, nitrate contamination of groundwater [58] and closure
of drinking water wells are a real problem for the basin’s water agencies and drinking
water suppliers. Pesticide contamination, associated with intensive agricultural
practices, is also an important concern in the basin [83].
5.2 Acting on Diffuse Agricultural Sources to Improve Water
Quality
Point source pollutions are today almost completely under control. Simultaneously,
diffuse agricultural sources, particularly of nitrogen, have become the subject of
particular concern because of their cascading effect on many compartments of the
environment [84]. Two contrasted scenarios of the future of the agro-food system
have been established and compared [85, 86]. The first one consists of the continuation of the current trends of opening and specialisation (O/S) of the conventional
cropping systems following regulation but without questioning the basic structural
features of the current production system. The second scenario (A/R/D) involves a
radical reorganisation of agricultural production, generalising organic farming practices, reconnecting livestock and crop farming [57, 87] and changing human consumption towards a Demitarian diet, i.e. cutting consumption of animal proteins by
Ecological Functioning of the Seine River: From Long-Term Modelling. . .
207