Environmental Engineering Reference
In-Depth Information
wavelengths 450-800 nm (Kowalczuk et al.
2003
), which is usually not observed
in marine waters. This might be due to the large amount of humic substances in
freshwater, which absorb radiation at >450 nm. The riverine input of chromo-
phores contained in freshwater CDOM to the coastal marine environment usu-
ally meets photodegradation in the coastal areas, which significantly reduces the
CDOM content of seawater (del Vecchio and Blough
2002
; Vähätalo and Wetzel
2004
; Vähätalo et al.
2000
).
Excitation of electrons is a typical phenomenon in both CDOM chromophores
and FDOM fluorophores (Senesi
1990a
; Wu et al.
2005
). Therefore, the DOM
components contributing to CDOM and FDOM would be partially the same. On
the other hand, the fluorescent components in DOM are identified and distin-
guished on the basis of specific excitation-emission (Ex/Em) wavelength maxima
in EEM spectra, upon PARAFAC modeling (Coble
1996
; Fulton et al.
2004
; Cory
and McKnight
2005
; Hall et al.
2005
; Stedmon and Markager
2005a
,
2005b
; Ohno
and Bro
2006
; Stedmon et al.
2007a
,
2007b
; Mostofa et al.
2010
; Wu et al.
2003a
).
In contrast, it is not possible to identify and distinguish the specific CDOM com-
ponents due to the absence of peaks in the CDOM absorption spectra (del Vecchio
and Blough
2002
; Vähätalo and Wetzel
2004
; Vähätalo et al.
2000
).
The fluorescent organic substances that are usually identified in natural waters
using EEM spectra in combination with PARAFAC modeling are fulvic acid-like,
humic acid-like, autochthonous fulvic acids (C-like and M-like), protein-like, tryp-
tophan-like, tyrosine-like components, and fluorescent whitening agents (FWAs)-
like (Tables
1
,
2
). On the other hand, absorption spectra at 350, 355 or 375 nm
have been used to monitor the CDOM absorption properties (del Vecchio and
Blough
2004
,
2002
; Kowalczuk et al.
2003
,
2005
), and the specific UV absorb-
ance (SUVA) at 254 or 280 nm has been adopted to estimate the aromatic carbon
contents and to understand the chemical characteristics of DOM (Chin et al.
1994
;
Croué et al.
2003
; Weishaar et al.
2003
;
Ś
wietlik and Sikorska
2004
).
6.2 How Do Fluorophores in FDOM Differ from
Chromophores in CDOM?
The fluorophores in FDOM are expected to be fundamentally similar to the
chromophores in CDOM. For example, tryptophan amino acid (C
8
H
5
(NH)-
CH
2
(NH
3
)-CH-COO
−
(peak T) and C
8
H
5
(NH)- (peak T
UV
). The two fluorophores absorb photons and
are thus responsible for tryptophan absorption properties as well. In addition,
macromolecules such as allochthonous fulvic acid or humic acid are composed
of a number of fluorophores such as Schiff-base derivatives (-N
=
C-C
=
C-N-),
-COOH, -COOCH
3
, -OH, -OCH
3
, -CH
=
O, -C
=
O, -NH
2
, -NH-, -CH
=
CH-
COOH, -OCH
3
, S-, O- or N-containing aromatic compounds, and so on (Mostofa
et al.
2009a
; Senesi
1990a
; Leenheer and Croué
2003
; Malcolm
1985
; Corin et al.
1996
; Peña-Méndez et al.
2005
; Seitzinger et al.
2005
; Zhang et al.
2005
). These
+
)CHCOO
−
) has two fluorophores such as -CH
2
-(NH
3
+
