Geoscience Reference
In-Depth Information
February 2002
September 2002
September 2006
HIX
BIX
18
1
0.95
16
0.9
14
0.85
12
0.8
10
0.75
8
0.7
6
0.65
4
0.6
2
0.55
0
0.5
0
5
10
15
20
25
30
35
40
Salinity
Figure 9.16. Comparison of the BIX and HIX
EM
for an estuarine transect sampled on three dates. BIX
and HIX
EM
measurements were used to infer regions of different organic matter character, identified
by the vertical lines. These differences were attributed to fresh water from the river mixing with
saline marine water. (From Huguet et al.,
2009
.)
to reflect the marine (autochthonous and bacterial derived) organic matter and terrestrial
(allochthonous) end members.
Figure 9.7
demonstrates a trend typical of estuarine mixing
for BIX versus salinity, with high BIX values corresponding with highest salinity.
Huguet et al. (
2009
) suggested that the interpretation of the McKnight et al. (
2001
) FI
is complicated in an estuarine environment because peak C emission wavelength may vary
with salinity due to flocculation processes and changes in organic matter molecular weight.
The values they reported were much lower than those that have been reported for freshwa-
ters. Jaffé et al. (
2004
) came to similar conclusions about the difficulty in interpreting the
FI when applied to a mangrove environment. However, in a study of chromophoric DOM
in a fjord in New Zealand, Gonsoir et al. (
2008
) also found that the FI had low values in the
estuary and that the FI increased with depth in the upper 5 m. These results were interpreted
as suggesting that there was an increasing influence of marine-derived DOM at depth, or
that changes in the fluorophores occurred across the mixing zone in the fjord.
9.4 Spectroscopic Challenges toward Using the Indices
Fluorescence indices have proven to be powerful tools for analyzing dissolved organic mat-
ter as well as organic matter from soils and sediments. However, owing to the many factors
that affect fluorescence signatures, it is necessary to pay careful attention to collection and
correction of samples and data to properly utilize the indices. This section briefly reviews
