Environmental Engineering Reference
In-Depth Information
295/409 nm and 230/409 nm (Fig.
3
h). The results show that the excitation-emis-
sion (Ex/Em) wavelengths of both peaks C and A in fulvic acid-like substances
are shifted in the RU calibration compared to QSU. The fluorescence intensi-
ties of peak C in RU calibration are higher than in the peak A-region, which is
entirely opposite to QSU calibration. The fulvic acid-like components in QSU of
upstream waters (Fig.
2
a, b) are characteristically similar to standard Suwannee
River Fulvic Acid (Fig.
2
a, b). The fulvic acid-like component (component 1)
and autochthonous fulvic acid-like component (component 2) in QSU data of
lake waters are similar to their respective photo-bleaching components, which
have been detected in lake surface waters during the summer stratification period
(Mostofa et al.
2005b
). It can be noted that the PARAFAC modeling has been car-
ried out on published data of monthly samples collected at Nishi-Mayata upstream
(April, May, July, and August) and Lake Biwa surface waters (2.5, 10 and 20 m
depth for April, July, August and September) (Mostofa et al.
2005b
). The results
indicate once more that both the excitation-emission wavelength peaks and their
respective fluorescence intensities are significantly changed when using RU cali-
bration. Therefore, it is strongly recommended that the calibration of the fluores-
cence intensity data of EEM spectra is carried out using either the QSU method or
arbitrary units, avoiding the RU calibration method. It is also recommended that
before measurement of the samples, Xe-light in the fluorescence spectrophotom-
eter is corrected according to the instrument's guidelines using a Rhodamine B
solution.
2.5 EEM Properties and Molecular Characteristics
of Key FDOM Components Identified by PARAFAC
The molecular, chemical and EEM properties of the various FDOM components in
natural waters are discussed below.
Allochthonous Fulvic Acids (C-like, A-like and M-like)
Standard Suwannee River Fulvic Acid (SRFA) is composed of two fluorescent
components identified by PARAFAC modeling on its EEM. The first compo-
nent is denoted as allochthonous fulvic acid (C-like), which includes two fluo-
rescence peaks at Ex/Em
=
295-410/439-520 nm (peak C-region) and at Ex/
Em
=
240-270/439-520 nm (peak A-region) (Figs.
2
a,
3
a; Table
2
). The peak A
of the allochthonous fulvic acid (C-like) often has higher fluorescence intensity
(by ~1.30-3.0 times) compared to the peak C-region. Note that the Raman Unit
(RU) calibration often returns longer excitation wavelengths, particularly at the
peak C-region, compared to standard quinine sulfate (or other) calibration. The
allochthonous fulvic acid (C-like) is identified at Ex/Em
=
325-340/442-462 nm
and 250-260/450-451 nm for standard SRFA dissolved in Milli-Q waters. The
corresponding wavelengths are 345/452 and 255/451 nm for SRFA dissolved in
