Environmental Engineering Reference
In-Depth Information
This chapter will give a general overview on the sources and nature of colored and
CDOM, biogeochemical functions of CDOM, optical variables, chromophores in the
CDOM, and the theory of CDOM absorbance in natural waters. Moreover, the con-
trolling factors of CDOM that are most important in natural waters will be discussed.
Two key factors such as photoinduced and microbial changes in CDOM are also dis-
cussed. Finally, a discussion is devoted to the importance of CDOM in natural waters.
1.1 Key Biogeochemical Functions of CDOM
The biogeochemical functions of DOM (discussed in chapter
“
Dissolved Organic
Matter in Natural Waters
”) have many similarities with those of CDOM, because
DOM contains both colored and chromophoric DOM. The key biogeochemi-
cal functions of CDOM associated with natural waters are reported as follows.
(i) Distribution of colored DOM in the ocean could be a useful indicator for bet-
ter understanding DOC contents and distribution (del Vecchio and Blough
2004
;
Hayase et al.
1987
; Vodacek et al.
1995
; Ferrari et al.
1996
; Stabenau and Zika
2004
; Prahl and Coble
1994
), salinity distribution (Laane and Kramer
1990
;
Dorsch and Bidleman
1982
; Willey and Atkinson
1982
; Carder et al.
1993
), water
mass mixing (Hujerslev et al.
1996
; Nieke et al.
1997
) and pollutant dispersion
(Laane and Kramer
1990
). (ii) Colored DOM (mostly allochthonous fulvic and
humic acids, and autocthonous fulvic acids) is responsible for the photoinduced
generation of hydrogen peroxide (H
2
O
2
) and organic peroxides (ROOH) and for
initiation of photo-oxidation processes in natural waters upon sunlight absorption
(Mostofa and Sakugawa
2009
; Moore et al.
1993
; Vione et al.
2006
; Richard et al.
2007
; al Housari et al.
2010
; Clark et al.
2009
; Minella et al.
2011
). (iii) Colored
DOM is partially responsible for the photoinduced generation of hydroxyl radi-
cals (HO
•
), strong oxidizing agents that may decompose the colored CDOM itself
and other organic substances in aqueous media (Minero et al.
2007
; Vione et al.
2006
). The production of HO
•
by CDOM could take place upon water oxidation by
the triplet states
3
CDOM* or through formation of H
2
O
2
, either upon direct pho-
toinduced dissociation (H
2
O
2
+
h
υ
→
2HO
•
) or through Fenton or photo-Fenton
decomposition (Zepp et al.
1992
; Legrini et al.
1993
; Von Sonntag et al.
1993
;
Takeda et al.
2004
; Nakatani et al.
2007
). (iv) The absorption of light by chromo-
phores in CDOM initiates several important processes in natural waters such as the
release of heat (Kirk
1988
), the production of luminescence (Coble
1996
; Vodacek
et al.
1995
; del Castillo and Miller
2008
; Blough and Green
1995
) and the forma-
tion of numerous photo products (Ma and Green
2004
; Moran and Zepp
1997
;
Corin et al.
1996
; Miller
1998
; Blough and Zepp
1995
). (v) Photodegradation of
CDOM in surface waters results in the direct loss of absorption and fluorescence
that lead to a decrease in the number of the chromophores of CDOM, thereby caus-
ing a decline of CDOM's absorption properties and photoinduced nature (Moran
et al.
2000
; Skoog et al.
1996
; Reche et al.
1999
; Whitehead and Vernet
2000
;
Twardowski and Donaghay
2001
; del Vecchio and Blough
2002
; Mostofa et al.
