with excess phosphorus (P) and/or nitrogen (N) limits the growth of siliceous algae
such as diatoms, possibly leading to severe and undesirable ecosystem shifts [5].
Among the four-dimensional nature of lotic ecosystems [6], the longitudinal
upstream–downstream dimension was the leading factor, inspired by the River
Continuum Concept (RCC) describing the longitudinal auto- vs. heterotrophic
metabolism pattern [7]. A river system can be considered as a network of connected
river stretches of different stream orders [8], each characterised by a common
scheme of ecological and biogeochemical processes, whose intensities depend on
local hydro-morphological features and on inputs received from the upstream
network and the watershed. The metabolism in each of the network’s ecosystems
is therefore dependent on its position in the network (its stream order for river
stretches), and all ecosystems are collectively influenced by the water runoff flowing
through the system as well as by the point and diffuse sources of nutrients originating
from the watershed. At the outlet of the system, water and nutrients are exported to
marine coastal zones, the functioning of which can be strongly influenced by these
inputs.
Taking into account the role of connected stagnant ecosystems [9–11], as well as
denitrification in riparian zones [12, 13], allows the investigation of the lateral
dimension in the sense of water interactions with drained terrestrial parts of a
watershed [6]. Whereas [14–17] investigated the vertical dimension, i.e. water and
nutrient exchanges between aquifers and surface water [18, 19] in the context of a
multi-scale view of stream–aquifer interfaces [20], the fourth dimension, which
provides the time scale, has long been a major concern of the PIREN-Seine program,
both in terms of past and future scenario analysis [21, 22].
The Seine River system is a textbook example illustrating this overall vision.
It drains one of the most intensive agricultural areas in the world, as well as one of
the largest European metropolises. The population is mostly concentrated along the
main downstream stretch (seventh order), 150 km upstream from the beginning of
the estuarine zone. Water quality problems related to urban organic pollution and
eutrophication were very acute at the beginning of the PIREN-Seine program and
have been largely repaired over the last few decades.
In this chapter we first provide a short summary of the methodologies used in
our studies of the Seine River metabolism, based on a combination of field
measurements and modelling approaches. We then describe the long-term changes
in organic matter and nutrient contamination of the system, followed by a discussion on the metabolism of river ecosystems in terms of auto- and heterotrophy as
well as gas production. Finally, a prospective view of the river functioning
concludes the chapter.
Ecological Functioning of the Seine River: From Long-Term Modelling. . .
191
such as diatoms, possibly leading to severe and undesirable ecosystem shifts [5].
Among the four-dimensional nature of lotic ecosystems [6], the longitudinal
upstream–downstream dimension was the leading factor, inspired by the River
Continuum Concept (RCC) describing the longitudinal auto- vs. heterotrophic
metabolism pattern [7]. A river system can be considered as a network of connected
river stretches of different stream orders [8], each characterised by a common
scheme of ecological and biogeochemical processes, whose intensities depend on
local hydro-morphological features and on inputs received from the upstream
network and the watershed. The metabolism in each of the network’s ecosystems
is therefore dependent on its position in the network (its stream order for river
stretches), and all ecosystems are collectively influenced by the water runoff flowing
through the system as well as by the point and diffuse sources of nutrients originating
from the watershed. At the outlet of the system, water and nutrients are exported to
marine coastal zones, the functioning of which can be strongly influenced by these
inputs.
Taking into account the role of connected stagnant ecosystems [9–11], as well as
denitrification in riparian zones [12, 13], allows the investigation of the lateral
dimension in the sense of water interactions with drained terrestrial parts of a
watershed [6]. Whereas [14–17] investigated the vertical dimension, i.e. water and
nutrient exchanges between aquifers and surface water [18, 19] in the context of a
multi-scale view of stream–aquifer interfaces [20], the fourth dimension, which
provides the time scale, has long been a major concern of the PIREN-Seine program,
both in terms of past and future scenario analysis [21, 22].
The Seine River system is a textbook example illustrating this overall vision.
It drains one of the most intensive agricultural areas in the world, as well as one of
the largest European metropolises. The population is mostly concentrated along the
main downstream stretch (seventh order), 150 km upstream from the beginning of
the estuarine zone. Water quality problems related to urban organic pollution and
eutrophication were very acute at the beginning of the PIREN-Seine program and
have been largely repaired over the last few decades.
In this chapter we first provide a short summary of the methodologies used in
our studies of the Seine River metabolism, based on a combination of field
measurements and modelling approaches. We then describe the long-term changes
in organic matter and nutrient contamination of the system, followed by a discussion on the metabolism of river ecosystems in terms of auto- and heterotrophy as
well as gas production. Finally, a prospective view of the river functioning
concludes the chapter.
Ecological Functioning of the Seine River: From Long-Term Modelling. . .
191