POM depend on the surrounding watershed and on the hydrological connectivity
between the main channel, backwaters and groundwater, which control the transfer
of terrestrial and aquatic-derived OM in freshwater ecosystems [4]. Despite the
conventional agreement that terrestrial organic carbon is recalcitrant and transported
conservatively along streams and rivers with little contribution to aquatic metabolism, recent studies indicate that it is much less refractory and has a greater
bioavailability than previously thought [4, 6, 7].
OM plays an essential role in shaping aquatic ecosystems [8] because of the
number of processes in which it becomes involved. Whatever its sources, it has
a pivotal role in the autotrophy/heterotrophy balance in river systems, as described
in detail in Garnier et al. [9]. OM is also well known to influence the speciation,
solubility, toxicity and transport of organic and inorganic pollutants [10, 11]. Furthermore, DOM is also involved in aqueous photochemical reactions, nutrient cycling and
availability [12, 13]. The mechanisms involved in all these processes are strongly
dependent not only on the overall concentration of OM but also on its chemical nature,
physicochemical properties and composition in the aquatic environment. Moreover,
human activities alter fluvial NOM properties with OM inputs from agricultural and
forest practices as well as urban, domestic and industrial sewage [1, 2]. OM is also
a major concern in wastewater and drinking water treatments [14–16], affecting the
efficiency of water treatment processes, the colour, odour and taste in water and
resulting in the formation of disinfection by-products [15–17].
Despite their key role in environmental processes, OM composition and reactivity
are still poorly understood. The characterisation of OM and its influence on the
speciation of pollutants have been investigated, since 2010, in the Seine River
system, as described in this chapter, and contribute to new insights into the role of
OM in freshwater ecosystem functioning, its spatial and seasonal variability and its
interaction with contaminants. This chapter focuses most particularly on the distinction between different OM sources, including urban point sources, interactions with
watershed soils and in-stream processes.
The discharge of wastewater (treated or not) is a significant source of organic
matter for the Seine River. A major trend in the trajectory of the Seine River system
over the past 50 years has been the gradual improvement of wastewater treatment
and the reduction in the loading of point sources of contamination to the river.
The long-term trends in water quality and especially the changes in organic pollution
from urban point sources are fully described in the Chapter 8. Globally, the quality
of wastewater treatment has been very strongly and gradually improved since the
1970s [18]. Between 1970 and 1980, the flow of biochemical oxygen demand
(BOD 5 ) discharged into the river decreased from 70,000 tonnes year
À1 to 45,000
tonnes year
À1 . This flow remains constant until 1995 and then decreases sharply to
reach 20,000 tonnes year
À1 in 2005 and 10,000 tonnes year
À1 in 2015. The decrease
occurred later for Kjeldahl nitrogen, i.e. from 30,000 tonnes year
À1 between 1987
and 2007 to less than 10,000 tonnes year
À1 since 2007, following the commissioning
of the nitrification unit at the Seine-Aval wastewater treatment plant (WWTP) [18].
Despite the very significant improvement in wastewater treatment and thus in water
quality in the Seine River over the past 50 years, questions still remain on the role
of OM in the transport of nutrients and contaminants from land to sea and on the
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
219
between the main channel, backwaters and groundwater, which control the transfer
of terrestrial and aquatic-derived OM in freshwater ecosystems [4]. Despite the
conventional agreement that terrestrial organic carbon is recalcitrant and transported
conservatively along streams and rivers with little contribution to aquatic metabolism, recent studies indicate that it is much less refractory and has a greater
bioavailability than previously thought [4, 6, 7].
OM plays an essential role in shaping aquatic ecosystems [8] because of the
number of processes in which it becomes involved. Whatever its sources, it has
a pivotal role in the autotrophy/heterotrophy balance in river systems, as described
in detail in Garnier et al. [9]. OM is also well known to influence the speciation,
solubility, toxicity and transport of organic and inorganic pollutants [10, 11]. Furthermore, DOM is also involved in aqueous photochemical reactions, nutrient cycling and
availability [12, 13]. The mechanisms involved in all these processes are strongly
dependent not only on the overall concentration of OM but also on its chemical nature,
physicochemical properties and composition in the aquatic environment. Moreover,
human activities alter fluvial NOM properties with OM inputs from agricultural and
forest practices as well as urban, domestic and industrial sewage [1, 2]. OM is also
a major concern in wastewater and drinking water treatments [14–16], affecting the
efficiency of water treatment processes, the colour, odour and taste in water and
resulting in the formation of disinfection by-products [15–17].
Despite their key role in environmental processes, OM composition and reactivity
are still poorly understood. The characterisation of OM and its influence on the
speciation of pollutants have been investigated, since 2010, in the Seine River
system, as described in this chapter, and contribute to new insights into the role of
OM in freshwater ecosystem functioning, its spatial and seasonal variability and its
interaction with contaminants. This chapter focuses most particularly on the distinction between different OM sources, including urban point sources, interactions with
watershed soils and in-stream processes.
The discharge of wastewater (treated or not) is a significant source of organic
matter for the Seine River. A major trend in the trajectory of the Seine River system
over the past 50 years has been the gradual improvement of wastewater treatment
and the reduction in the loading of point sources of contamination to the river.
The long-term trends in water quality and especially the changes in organic pollution
from urban point sources are fully described in the Chapter 8. Globally, the quality
of wastewater treatment has been very strongly and gradually improved since the
1970s [18]. Between 1970 and 1980, the flow of biochemical oxygen demand
(BOD 5 ) discharged into the river decreased from 70,000 tonnes year
À1 to 45,000
tonnes year
À1 . This flow remains constant until 1995 and then decreases sharply to
reach 20,000 tonnes year
À1 in 2005 and 10,000 tonnes year
À1 in 2015. The decrease
occurred later for Kjeldahl nitrogen, i.e. from 30,000 tonnes year
À1 between 1987
and 2007 to less than 10,000 tonnes year
À1 since 2007, following the commissioning
of the nitrification unit at the Seine-Aval wastewater treatment plant (WWTP) [18].
Despite the very significant improvement in wastewater treatment and thus in water
quality in the Seine River over the past 50 years, questions still remain on the role
of OM in the transport of nutrients and contaminants from land to sea and on the
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
219