Geoscience Reference
In-Depth Information
10
2
C1 vs. C3
C2 vs. C4
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C2 vs. C5
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C3 vs. C5
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Intensity (RU) first component in pair
Figure 10.8. Paired comparisons between log-transformed fluorescence intensities of PARAFAC
components in the Horsens catchment data set. (See Plate 16.)
waste water (Stedmon, unpublished). The consistent relationship between C2 and C4 for
all except the wastewater samples suggests that they represent a common ubiquitous signal
from the streams that is traceable into, and sustained in, the estuary. In the plot relating C2
and C5, it is observed that wastewater, streams, and estuary sites form three distinct groups
in which wastewater and estuarine samples have a relatively greater proportion of C5, sug-
gesting biological production, relative to the terrestrial signal of C2.
Comparisons between the fluorescent components in the Horsens catchment model and
other published PARAFAC spectra for DOM samples are shown in
Figure 10.7
. Previous
studies hypothesize that humic-like C2, which has been identified in many previous mod-
els, is derived from terrestrial material (Stedmon et al.,
2003
; Murphy et al.,
2008
), possibly
as an intermediate formed during photochemical degradation of terrestrial organic matter
(Stedmon et al.,
2007
). Protein-like fluorescence including tryptophan-like C5 is associated
with biological production in surface waters (Determann et al.,
1994
; Determann et al.,
1998
). Humic-like C1 has an emission spectrum identical to syringealdehyde (produced in
the breakdown of lignin), and is associated with waters with high organic matter loadings
(Murphy et al.,
2011
). In this study, C1 dominated samples from forested upstream sites
(particularly sites R13 and R14 in the Hansted system), as well as at the WTP.
