Environmental Engineering Reference
In-Depth Information
is
F
Peak A/Peak C
, which is simple and can be easily applied to fluorescent com-
ponents identified using PARAFAC modeling (Table
3
; Fig.
4
). The
F
Peak A/Peak
C
is defined as the ratio of the maximum fluorescence intensity at peak A (peak
A-region) to that at peak C (peak C-region). For example, the maximum fluo-
rescence intensity of peak A for standard Suwannee River Fulvic Acid (n
=
5:
0.5-5 mg L
−
1
) identified using PARAFAC modeling (component 1) is 60 a.u. at
Ex/Em
=
260/463 nm and that for peak C is 39 a.u. at Ex/Em
=
330/463 nm for
the same component, which leads to
F
Peak A/Peak C
=
1.55 (Table
1
). The com-
parisons of the
F
Peak A/Peak C
values with other indices demonstrate that this new
index is very useful to identify the allochthonous fulvic acid (C-like) (1.30-1.80)
and allochthonous humic acid (1.50-1.95) from autochthonous fulvic acid of
algal origin (0.52-0.98) (Table
3
, Fig.
4
). Note that the
F
Peak A/Peak C
of autoch-
thonous fulvic acid (C-like) is relatively high (1.53) in the initial 10 days of
microbial assimilation of algae mixed with river waters (Table
3
). Photoinduced
degradation of fulvic acid in surface waters mostly causes a decrease in fluores-
cence intensity, which is more marked at peak C than at peak A and ultimately
causes an increase of the
F
Peak A/Peak C
values. This has also been found in irra-
diated SRFA (1.73), irradiated SRHA (1.94), irradiated fulvic acid in Kago
upstream (1.80), Yellow River upper waters (1.93), Yellow River downstream
waters (2.82), Yasu River waters (3.09) and lake surface waters (0-20 m) during
the summer stratification period in Lake Biwa (1.67-1.82). Therefore, high val-
ues (>1.30) of
F
Peak A/Peak C
can indicate the presence of photobleached fulvic or
humic acid whilst low values (<1) are associated with autochthonous fulvic acid
(C-like) of algal origin.
Low values of
F
Peak A/Peak C
for autochthonous fulvic acid (C-like) of algal ori-
gin also suggests the presence of high aromaticity with more functional groups
or fluorophores at peak C-region than at peak A region. Indeed, the highest fluo-
rescence intensity of algal-origin autochthonous DOM is often detected at peak
C-region than at peak A-region (Fig.
3
h-j). On the other hand, fulvic acid (ter-
restrial in origin) shows lower fluorescence intensity at peak C-region than at
peak A-region (Fig.
3
a), which indicates the presence of relatively low aromatic-
ity with a low number of functional groups or fluorophores and higher content
of aliphatic carbon (Mostofa et al.
2009a
,
b
; Malcolm
1985
). Such differences
in fluorescence intensities or fluorophores (functional groups) are attributed to
differences in the
f
findex
values, which would be useful in characterizing alloch-
thonous fulvic acid and autochthonous fulvic acid. However, there is no study
conducted on the chemical composition of algal-origin autochthonous DOM,
which would be the focus for future research. Some researchers believe that
autochthonously produced fulvic acid is similar to terrestrial fulvic acid, because
autochthonous DOM shows a yellow color as well as similar fluorescence prop-
erties. Therefore, the
f
findex
values can be useful to distinguish between the two
materials. On the other hand, allochthonous fulvic acid (M-like) can merely
be distinguished from the maximum fluorescence intensity of peak A (peak
A-region) and low fluorescence intensity of peak C (peak C-region) (Fig.
3
c)
whilst autochthonous fulvic acid (M-like) of algal (or phytoplankton) origin
