Environmental Engineering Reference
In-Depth Information
and Blough
2002
; Kowalczuk et al.
2003
; Green and Blough
1994
). This might
be due to the large quantities of humic substances in freshwaters, which usually
absorb radiation at
λ
> 450 nm. However, riverine input of chromophores con-
tained in freshwater CDOM to the coastal marine environment are decomposed
by photodegradation in the coastal area (Vähätalo and Wetzel
2004
; del Vecchio
and Blough
2002
; Vähätalo et al.
2000
). The combination of photodegradation
and dilution prevents large amount of freshwater CDOM to reach the open ocean.
Autochthonous CDOM usually increases relative to chlorophyll
a
concentration
in the surface waters of lakes and oceans (Zhang et al.
2009
; Sasaki et al.
2005
;
Mostofa et al.
2011
). It is therefore suggested that phytoplankton degradation
begins after the spring bloom in surface waters.
2.1 Sources and Nature of CDOM in Natural Waters
CDOM is generally originated from two key sources, allochthonous and autoch-
thonous. The key sources of allochthonous DOM that includes fulvic and humic
acids (humic substances) are vascular plant material and particulate detrital pools
in terrestrial soil ecosystems. On the other hand, the key contributors for autoch-
thonous DOM in natural waters and in sediment pore waters are phytoplank-
ton or algal biomass, bacteria, coral, coral reef, submerged aquatic vegetation,
seagrass and marsh- and mangrove forest. The sources and nature of CDOM are
very similar to those of DOM, which have been explained in detail in chapter
2.2 Chromophores in CDOM
A chromophore is defined as a part of an organic molecule (functional group)
with or without electron-donating heteroatoms such as N, O, and S, as a func-
tional group with a highly unsaturated aliphatic carbon chain, or as a molecule
with a structure that can hold up an electron or has extensive
π
-electron sys-
tems, which can absorb photons (light energy) with significant efficiency, causing
the promotion from the ground state to an excited one. The key chromophores
in a molecule or DOM in natural waters are -OH, -CH
=
O, -C
=
O, -COOH,
-COOCH
3
, -OCH
3
, -NH
2
, -NH-, -CH
=
CH-, -CH
=
CH-COOH, -OCH
3
,
-(NH
2
)CH-COOH, S-, O- or N-containing aromatic compounds, Schiff-base
derivatives (-N
=
C-C
=
C-N-) and so on (Mostofa et al.
2009a
; Malcolm
1985
;
Strome and Miller
1978
; Mopper and Stahovec
1986
; Kieber et al.
1990
; Mopper
et al.
1991
; Wetzel et al.
1995
; Mostofa and Sakugawa
2009
; Corin et al.
1996
;
Senesi
1990
; Leenheer and Croue
2003
; Peña-Méndez et al.
2005
; Seitzinger
et al.
2005
; Zhang et al.
2005
). Fulvic and humic acids of vascular plant ori-
gin have a molecular structure containing carboxy- and methoxy- benzenes and
