The organic carbon content was determined by POC and DOC hightemperature combustion measurements, and BDOC was assessed through incubation experiments [30].
Nuclear magnetic resonance (NMR) spectroscopy has been largely used to
investigate NOM structure [31]. To identify the main functional groups of OM
in the Seine River catchment, the solid-state
13 C NMR spectra were recorded for
POM isolated on glass fibre filters after filtration of 3–10 L of surface waters
collected from selected sampling sites during the low water (2012) and flooding
(2013) campaigns.
For selected sampling sites, about 10 L of surface waters collected in low water
(2012) and flooding (2013) periods were fractionated on non-ionic macroporous
DAX-8 and XAD-4 resins so as to separate DOM into different fractions according
to polarity criteria. The hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI)
fractions were thus isolated according to a protocol described elsewhere [29].
The application of optical properties as a proxy for DOM composition and
reactivity in aquatic environments has been extensively applied [28]. To
gain information on its origin, dynamics and degree of transformation, UV/visible
absorbance and excitation emission matrix (EEM) fluorescence spectroscopy
combined with parallel factor analysis (PARAFAC) were used to characterise
DOM in the Seine River watershed [32]. UV/visible absorbance spectroscopy
was used to determine DOM properties at natural pH. The spectral slope ratio
S R (S R ¼ S 275–295 nm /S 350–400 nm ) was used to estimate the variation of the molecular
weight of DOM; the molecular weight decreases when S R increases [33]. The
specific UV absorbance at 254 nm (SUVA 254 ) is strongly correlated with the
hydrophobic organic acid fraction of DOM and is a useful proxy for DOM aromatic
content and molecular weight [34]. Information on the origin and the transformation
degree of DOM can be obtained through the calculation of the humification index
(HIX) [35] and the biological index (BIX) [36].
2.3 Sources and Spatio-Temporal Variability of OM
in the Seine River Basin
For the three snapshot campaigns, DOC concentrations were not significantly
different among the Seine, Marne and Oise subbasins, whether it was in low or
high waters (about 3 mgC L
À1 ), with, however, slightly higher values observed
for the Oise subbasin. For the Seine River, DOC concentrations were higher
downstream of Paris, and this increase of DOC amounts between the upstream and
downstream of the Paris conurbation was more pronounced at low water. The
biodegradable fraction (BDOC), however, differed by a factor >4 (28% vs. 6% in
low water vs. high water, respectively). The Oise River was clearly distinguished
by its higher POC content in suspended solids during the high flow in February
2013, much higher than the values of the other subbasins.
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
223
Nuclear magnetic resonance (NMR) spectroscopy has been largely used to
investigate NOM structure [31]. To identify the main functional groups of OM
in the Seine River catchment, the solid-state
13 C NMR spectra were recorded for
POM isolated on glass fibre filters after filtration of 3–10 L of surface waters
collected from selected sampling sites during the low water (2012) and flooding
(2013) campaigns.
For selected sampling sites, about 10 L of surface waters collected in low water
(2012) and flooding (2013) periods were fractionated on non-ionic macroporous
DAX-8 and XAD-4 resins so as to separate DOM into different fractions according
to polarity criteria. The hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI)
fractions were thus isolated according to a protocol described elsewhere [29].
The application of optical properties as a proxy for DOM composition and
reactivity in aquatic environments has been extensively applied [28]. To
gain information on its origin, dynamics and degree of transformation, UV/visible
absorbance and excitation emission matrix (EEM) fluorescence spectroscopy
combined with parallel factor analysis (PARAFAC) were used to characterise
DOM in the Seine River watershed [32]. UV/visible absorbance spectroscopy
was used to determine DOM properties at natural pH. The spectral slope ratio
S R (S R ¼ S 275–295 nm /S 350–400 nm ) was used to estimate the variation of the molecular
weight of DOM; the molecular weight decreases when S R increases [33]. The
specific UV absorbance at 254 nm (SUVA 254 ) is strongly correlated with the
hydrophobic organic acid fraction of DOM and is a useful proxy for DOM aromatic
content and molecular weight [34]. Information on the origin and the transformation
degree of DOM can be obtained through the calculation of the humification index
(HIX) [35] and the biological index (BIX) [36].
2.3 Sources and Spatio-Temporal Variability of OM
in the Seine River Basin
For the three snapshot campaigns, DOC concentrations were not significantly
different among the Seine, Marne and Oise subbasins, whether it was in low or
high waters (about 3 mgC L
À1 ), with, however, slightly higher values observed
for the Oise subbasin. For the Seine River, DOC concentrations were higher
downstream of Paris, and this increase of DOC amounts between the upstream and
downstream of the Paris conurbation was more pronounced at low water. The
biodegradable fraction (BDOC), however, differed by a factor >4 (28% vs. 6% in
low water vs. high water, respectively). The Oise River was clearly distinguished
by its higher POC content in suspended solids during the high flow in February
2013, much higher than the values of the other subbasins.
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
223