weight DOM, whereas waters with SUVA 254 values 2–3 L mg
À1 C m
À1 contain a
mixture of hydrophobic and hydrophilic DOM from various sources with a range of
molecular weights. The highest SUVA 254 value was determined for one sample from
the Oise River in 2011 (5.3 L mg
À1 C m
À1 ), reflecting a relatively high content of
complex heterogeneous macromolecular organic compounds rich in aromatics,
while DOM in all other samples exhibited lower SUVA 254 values (1.0–3.8 L mg
À1 C m
À1 ), implying a wide range of DOM characteristics and molecular
weights [32].
All surface waters were then analysed using EEM fluorescence spectroscopy
as previously described [36, 37]. Spatial and temporal variations of DOM quality
were highlighted according to hydrological conditions [32]. The higher concentrations of fluorescent materials were found for waters collected in 2011 (low water)
in comparison to those sampled in 2012 (low water) and in 2013 (flooding). The
HIX [35] and BIX [36] indices were calculated to gain information on DOM origin
and transformation. The highest HIX values, corresponding to aromatic and mature
organic material, were observed in the Oise basin with maxima in the forest
zones (!20). A relatively high biological activity (BIX > 0.6) characterised all
the samples, the highest values (BIX > 0.75) being observed for the Seine River in
2011 and 2012 and in the Marne River basin in 2012. The flood period (2013) was
characterised by high HIX values (mainly ! 10), while the lowest values were
observed during the low-water stage (2012), mainly associated with high BIX
values, indicating a strong biological activity for these samples [32].
A seven-component model was determined by PARAFAC analysis, explaining
99.8% of the total data set (102 surface water samples) variability [32]. The EEM
spectra contour plots of the seven components are given Fig. 3 (top). The seven
components determined showed similarities, with peaks identified in previous
studies and related in the literature [32]. Components 4, 5, 6 and 7 were related
to biological activity, while components 1, 2 and 3 to aromatic and mature terrestrial
material (C1 and C2 being mainly linked to aromaticity).
The distributions of these components within the different subbasins and
according to the sampling periods are given in Fig. 3 (bottom). Three types of OM
were distinguished, the Seine River sub-catchment being mainly characterised by
the strongest biological activity, the Oise River subbasin by more terrestrial signatures (even more pronounced for samples taken from forest areas) and a part of
the Marne River basin by a third specific type of OM, with a higher contribution
of component 7 in particular.
The highest biological signature determined in the Seine River was for samples
collected downstream from Paris, pointing out the impact of urban discharges on
DOM properties [32]. Moreover, mature DOM of terrestrial origin characterised the
samples collected during the flood, while samples collected in the Seine River
and the Marne River subbasins during low-water periods (2011 and 2012) were
composed of constituents derived from biological activity. However, at low water,
a terrestrial signature still described the Oise River sub-catchment. Furthermore,
during the flood period, a similar distribution of the seven components was observed
for all the samples, whatever the river subbasin, demonstrating a predominant source
of terrigenous DOM in the entire watershed.
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
225
À1 C m
À1 contain a
mixture of hydrophobic and hydrophilic DOM from various sources with a range of
molecular weights. The highest SUVA 254 value was determined for one sample from
the Oise River in 2011 (5.3 L mg
À1 C m
À1 ), reflecting a relatively high content of
complex heterogeneous macromolecular organic compounds rich in aromatics,
while DOM in all other samples exhibited lower SUVA 254 values (1.0–3.8 L mg
À1 C m
À1 ), implying a wide range of DOM characteristics and molecular
weights [32].
All surface waters were then analysed using EEM fluorescence spectroscopy
as previously described [36, 37]. Spatial and temporal variations of DOM quality
were highlighted according to hydrological conditions [32]. The higher concentrations of fluorescent materials were found for waters collected in 2011 (low water)
in comparison to those sampled in 2012 (low water) and in 2013 (flooding). The
HIX [35] and BIX [36] indices were calculated to gain information on DOM origin
and transformation. The highest HIX values, corresponding to aromatic and mature
organic material, were observed in the Oise basin with maxima in the forest
zones (!20). A relatively high biological activity (BIX > 0.6) characterised all
the samples, the highest values (BIX > 0.75) being observed for the Seine River in
2011 and 2012 and in the Marne River basin in 2012. The flood period (2013) was
characterised by high HIX values (mainly ! 10), while the lowest values were
observed during the low-water stage (2012), mainly associated with high BIX
values, indicating a strong biological activity for these samples [32].
A seven-component model was determined by PARAFAC analysis, explaining
99.8% of the total data set (102 surface water samples) variability [32]. The EEM
spectra contour plots of the seven components are given Fig. 3 (top). The seven
components determined showed similarities, with peaks identified in previous
studies and related in the literature [32]. Components 4, 5, 6 and 7 were related
to biological activity, while components 1, 2 and 3 to aromatic and mature terrestrial
material (C1 and C2 being mainly linked to aromaticity).
The distributions of these components within the different subbasins and
according to the sampling periods are given in Fig. 3 (bottom). Three types of OM
were distinguished, the Seine River sub-catchment being mainly characterised by
the strongest biological activity, the Oise River subbasin by more terrestrial signatures (even more pronounced for samples taken from forest areas) and a part of
the Marne River basin by a third specific type of OM, with a higher contribution
of component 7 in particular.
The highest biological signature determined in the Seine River was for samples
collected downstream from Paris, pointing out the impact of urban discharges on
DOM properties [32]. Moreover, mature DOM of terrestrial origin characterised the
samples collected during the flood, while samples collected in the Seine River
and the Marne River subbasins during low-water periods (2011 and 2012) were
composed of constituents derived from biological activity. However, at low water,
a terrestrial signature still described the Oise River sub-catchment. Furthermore,
during the flood period, a similar distribution of the seven components was observed
for all the samples, whatever the river subbasin, demonstrating a predominant source
of terrigenous DOM in the entire watershed.
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
225