(950 m
3 s
À1 ), the DOC increase at the downstream site compared to the upstream
sites was less than 0.5 mgC L
À1 , while it reached 1.5 mgC L
À1 during periods of low
water (100–200 m
3 s
À1 ). These values are fully consistent with DOC concentrations
in the range of 10–15 mgC L
À1 in treated effluent from the Seine-Aval WWTP.
Regarding the DOC distribution between HPI, TPI and HPO fractions at
upstream and downstream sites, a high temporal variability can be observed. Indeed,
the hydrophobic fraction (HPO) exceeded 60% in November when soil runoff and
leaching started again and then decreased during winter floods (45% of the DOC).
The lowest values, less than 30%, were observed during low-water periods due to
autochthonous production as well as the lower terrigenous input. The spatial variability between the upstream and downstream sites is quite clear: the HPI fraction
accounts for about 50% of DOC in low water (between March and September 2011)
at the downstream site and only around 40% at upstream sites. This increase of the
HPI fraction at the downstream site is probably due to effluent dissolved organic
matter (EfDOM) from WWTPs.
From these data, instantaneous DOC fluxes and DOC flux distribution according
to the HPO, TPI and HPI fractions were determined. For each sampling campaign,
the DOC flux increased across the Paris conurbation, but the higher increase was
noted during low-water periods (from March to September): the DOC flux increase
was on average 100%, 140% for the HPI fraction and 75% for both HPO and TPI
fractions. This means that in the receiving environment downstream of the agglomeration, during low-water periods, 50% of the DOC came from EfDOM, and this
proportion reached nearly 60% for HPI DOC.
This increase in DOC flux through the Paris conurbation area was greater during
low-water periods due to the lower dilution of EfDOM. This flux increase was
particularly high for the HPI fraction, which is fully consistent with the distribution
of DOC observed in EfDOM [29]. These results therefore demonstrate that, even
with the very significant improvement in wastewater treatment over the past
50 years, EfDOM of the Paris conurbation remains a very important DOM source
for the Seine River. It has a very strong impact on DOM present downstream, both
in terms of quantity and quality, causing a significant increase in hydrophilicity
downstream of the agglomeration.
3 Influence of Organic Matter on the Fate
of Micro-pollutants and the Role Played by Urban
Organic Matter
3.1 Context
In receiving waters, DOM is a key component of both trace metal speciation [10] and
bioavailability [11, 39]. Many studies have highlighted the trace metal-binding
ability of DOM in surface waters [10, 11, 40], yet the majority of published works
generally concern either the DOM collected from surface waters not affected by
228
G. Varrault et al.
3 s
À1 ), the DOC increase at the downstream site compared to the upstream
sites was less than 0.5 mgC L
À1 , while it reached 1.5 mgC L
À1 during periods of low
water (100–200 m
3 s
À1 ). These values are fully consistent with DOC concentrations
in the range of 10–15 mgC L
À1 in treated effluent from the Seine-Aval WWTP.
Regarding the DOC distribution between HPI, TPI and HPO fractions at
upstream and downstream sites, a high temporal variability can be observed. Indeed,
the hydrophobic fraction (HPO) exceeded 60% in November when soil runoff and
leaching started again and then decreased during winter floods (45% of the DOC).
The lowest values, less than 30%, were observed during low-water periods due to
autochthonous production as well as the lower terrigenous input. The spatial variability between the upstream and downstream sites is quite clear: the HPI fraction
accounts for about 50% of DOC in low water (between March and September 2011)
at the downstream site and only around 40% at upstream sites. This increase of the
HPI fraction at the downstream site is probably due to effluent dissolved organic
matter (EfDOM) from WWTPs.
From these data, instantaneous DOC fluxes and DOC flux distribution according
to the HPO, TPI and HPI fractions were determined. For each sampling campaign,
the DOC flux increased across the Paris conurbation, but the higher increase was
noted during low-water periods (from March to September): the DOC flux increase
was on average 100%, 140% for the HPI fraction and 75% for both HPO and TPI
fractions. This means that in the receiving environment downstream of the agglomeration, during low-water periods, 50% of the DOC came from EfDOM, and this
proportion reached nearly 60% for HPI DOC.
This increase in DOC flux through the Paris conurbation area was greater during
low-water periods due to the lower dilution of EfDOM. This flux increase was
particularly high for the HPI fraction, which is fully consistent with the distribution
of DOC observed in EfDOM [29]. These results therefore demonstrate that, even
with the very significant improvement in wastewater treatment over the past
50 years, EfDOM of the Paris conurbation remains a very important DOM source
for the Seine River. It has a very strong impact on DOM present downstream, both
in terms of quantity and quality, causing a significant increase in hydrophilicity
downstream of the agglomeration.
3 Influence of Organic Matter on the Fate
of Micro-pollutants and the Role Played by Urban
Organic Matter
3.1 Context
In receiving waters, DOM is a key component of both trace metal speciation [10] and
bioavailability [11, 39]. Many studies have highlighted the trace metal-binding
ability of DOM in surface waters [10, 11, 40], yet the majority of published works
generally concern either the DOM collected from surface waters not affected by
228
G. Varrault et al.