The HPO, TPI and HPI fractions were isolated, according to DOM polarity, from
14 surface water samples collected in the low-water period in 2012 and 17 during
flooding in 2013. At low-water period, the proportion of DOC in the different
fractions showed little variation between sampling sites with the HPO, TPI and
HPI fractions averaging 31%, 27% and 42% of DOC, respectively. The HPI
proportion was slightly higher in the subbasins of the Marne River and the Seine
River, however. These results point out the higher presence of fresh autochthonous
DOM at this low-water period. During flooding, the distribution of DOC was also
homogenous between the three fractions, with 43%, 29% and 28% for the HPO, TPI
and HPI fractions, respectively. A strong increase of the hydrophobic fraction
(+40%) and a decrease of the hydrophilic fraction highlighted greater terrestrial
inputs for this hydrological condition.
The structural characterisation of POM was investigated by
13 C NMR analysis of
a few selected samples, representative of the whole Seine River watershed. The
analysis of the
13 C NMR spectra demonstrated great spatial variability of POM
characteristics. Samples from the Oise River and the upstream Seine River collected
in 2012, during a low-water period, were characterised by fresh OM, mainly polysaccharides, with also a high terrestrial contribution revealed by the presence of
lignin. Spectra of samples collected in the upstream Oise River and in the Seine
River downstream of Paris at the same period showed a decrease of aliphatic carbon
and carbohydrate signals with a relative increase of the aromatic carbon signal,
highlighting the presence of more humified organic material. Except for one location
in the upstream Oise River, differences were observed between spectra recorded for
all sampling sites in low-water and flood conditions. During flooding, POM for
samples in the Oise River and the upstream Seine River exhibited more aromatic
characteristics, while fresh material was observed in the upstream Oise River, in
contrast to results for the low-water stage. For the two samples in the Oise River and
the upstream Seine River, the lower freshness character of OM observed with a
higher DOC content could suggest an input of OM from groundwater. Conversely,
soil surface leaching could explain the presence of more recent OM and higher DOC
levels for the upstream Oise River sample. A high spatial and temporal variability of
POM characteristics depending on hydrological connectivity and conditions was
thus highlighted by
13 C NMR analysis.
The optical properties of DOM were determined, after filtration, for all surface
water samples collected during the three snapshot campaigns.
The highest values of S R were observed for samples collected from the Marne
River in low-water periods (2011 and 2012), reflecting the presence of lower
molecular weight OM in this area, whereas we noted, for all the sampling sites
in 2013 (flooding), the lowest S R values, corresponding to higher-molecular-weight
OM. Three of the four samples collected from the Grand Morin River in 2011
were also characterised by organic components of high molecular weight (HMW;
low S R values) as in the 2013 flood. As for the samples of the Seine River in 2012,
they were characterised by low-molecular-weight (LMW) DOM and especially
upstream of Paris [32].
It is considered that natural waters with high SUVA 254 values (!4 L mg
À1 C m
À1 )
have relatively high contents of hydrophobic, aromatic and high-molecular224
G. Varrault et al.
14 surface water samples collected in the low-water period in 2012 and 17 during
flooding in 2013. At low-water period, the proportion of DOC in the different
fractions showed little variation between sampling sites with the HPO, TPI and
HPI fractions averaging 31%, 27% and 42% of DOC, respectively. The HPI
proportion was slightly higher in the subbasins of the Marne River and the Seine
River, however. These results point out the higher presence of fresh autochthonous
DOM at this low-water period. During flooding, the distribution of DOC was also
homogenous between the three fractions, with 43%, 29% and 28% for the HPO, TPI
and HPI fractions, respectively. A strong increase of the hydrophobic fraction
(+40%) and a decrease of the hydrophilic fraction highlighted greater terrestrial
inputs for this hydrological condition.
The structural characterisation of POM was investigated by
13 C NMR analysis of
a few selected samples, representative of the whole Seine River watershed. The
analysis of the
13 C NMR spectra demonstrated great spatial variability of POM
characteristics. Samples from the Oise River and the upstream Seine River collected
in 2012, during a low-water period, were characterised by fresh OM, mainly polysaccharides, with also a high terrestrial contribution revealed by the presence of
lignin. Spectra of samples collected in the upstream Oise River and in the Seine
River downstream of Paris at the same period showed a decrease of aliphatic carbon
and carbohydrate signals with a relative increase of the aromatic carbon signal,
highlighting the presence of more humified organic material. Except for one location
in the upstream Oise River, differences were observed between spectra recorded for
all sampling sites in low-water and flood conditions. During flooding, POM for
samples in the Oise River and the upstream Seine River exhibited more aromatic
characteristics, while fresh material was observed in the upstream Oise River, in
contrast to results for the low-water stage. For the two samples in the Oise River and
the upstream Seine River, the lower freshness character of OM observed with a
higher DOC content could suggest an input of OM from groundwater. Conversely,
soil surface leaching could explain the presence of more recent OM and higher DOC
levels for the upstream Oise River sample. A high spatial and temporal variability of
POM characteristics depending on hydrological connectivity and conditions was
thus highlighted by
13 C NMR analysis.
The optical properties of DOM were determined, after filtration, for all surface
water samples collected during the three snapshot campaigns.
The highest values of S R were observed for samples collected from the Marne
River in low-water periods (2011 and 2012), reflecting the presence of lower
molecular weight OM in this area, whereas we noted, for all the sampling sites
in 2013 (flooding), the lowest S R values, corresponding to higher-molecular-weight
OM. Three of the four samples collected from the Grand Morin River in 2011
were also characterised by organic components of high molecular weight (HMW;
low S R values) as in the 2013 flood. As for the samples of the Seine River in 2012,
they were characterised by low-molecular-weight (LMW) DOM and especially
upstream of Paris [32].
It is considered that natural waters with high SUVA 254 values (!4 L mg
À1 C m
À1 )
have relatively high contents of hydrophobic, aromatic and high-molecular224
G. Varrault et al.