Geoscience Reference
In-Depth Information
2.0
LF
WLG
LF
1.9
1.8
LH
PL
1.7
WL
SL
1.6
OhR
ShR
1.5
MR
SuR
ShR
CR
DC
1.4
OgR
YR
1.3
SR
SuR
1.2
1.1
1.0
10
12
14
16
18
20
Aromaticity (%)
22
24
26
28
30
38
microbially derived
shingobee area
terrestrially derived
linear regression
large rivers
power fn regression
Figure 9.6. Plot of McKnight et al. (
2001
) fluorescence index (FI) vs. % aromaticity for a variety of
isolated fulvic acid samples. The % aromaticity was calculated using
13
C-NMR as the ratio of the area
of the aromatic carbon region to the total area of the spectrum. There is a strong correlation between
FI and % aromaticity (linear regression equation is
y
= -0.027
x
+ 2.1 (
R
2
= 0.85), and the power func-
tion regression is
y =
3.94
x
-0.316
where
x
= % aromaticity and
y
= FI). Note that while Deer Creek
(DC) flows into Snake River (SR), the aromaticity drops due to the aromatic fulvic acids sorbing to
iron oxide in the streambed, but there is little change in the FI, indicating a robustness of the index.
Site codes: DC = Deer Creek, LF = Lake Fryxell, LH = Lake Hoare, MR = Missouri River, OgR =
Ogeechee River, OhR = Ohio River, PL = Pony Lake, SL = Shingobee Lake, ShR = Shingobee River,
SR = Snake River, SuR = Suwanee River, WL = Williams Lake, WLg = Williams Lake groundwater,
YR = Yakima River. (From McKnight et al. [
2001
] where site descriptions are presented.)
a data set of EEMs from 379 samples that included fulvic acid extracts and whole waters
from oxic and anoxic zones of diverse lakes, streams, and wetlands, including those in
the Dry Valleys, alpine watersheds in Colorado, and an Arctic tundra in Alaska. Cory and
McKnight (
2005
) used parallel factor analysis (PARAFAC) to develop a 13-component
model that included 7 components with absorption and emission spectra that were similar
to those of various model quinone compounds. (See
Chapter 10
for details of PARAFAC
analysis.) Three components were identified as representing oxidized quinone-like moie-
ties (Q1, Q2, and Q3), three components represent semiquinone-like moieties (SQ1, SQ2,
and SQ3), and one component represents a reduced hydroquione-like moiety (HQ). They
identified a strong correlation between the FI and a relationship between two of these
components (SQ1 and SQ2 [
Figure 9.7
]). These components had dual absorption peaks,
one of which was centered on ~370 nm with emission peaks in the peak C range. The SQ2
component was resolved in a simpler PARAFAC model based only on the EEMs for the
Antarctic lakes and was relatively more important in samples with higher FIs. Cory et al.
