Environmental Engineering Reference
In-Depth Information
experimental and field observations of natural waters (Corin et al.
1996
; Yoshioka
et al.
2007
; Wu et al.
2005
; Morris and Hargreaves
1997
). (ii) Formation of micro-
biologically labile organic substances, which is commonly observed in the epilim-
nion of natural waters (Bertilsson and Tranvik
2000
,
1998
; Moran and Zepp
1997
).
(iii) Formation of CO, CO
2
and dissolved inorganic carbon (DIC, which is usually
defined as the sum of dissolved CO
2
, H
2
CO
3
, HCO
3
, and CO
3
2
−
), which is gen-
erally observed upon photodegradation of DOM (Ma and Green
2004
; Bertilsson
and Tranvik
2000
; Granéli et al.
1998
; Valentine and Zepp
1993
; Miller and Moran
1997
). (iv) Formation of N-containing (NH
4
−
+
−
) and P-containing inorganic
compounds, which may typically be produced by degradation of dissolved organic
nitrogen (DON) and dissolved organic phosphorus (DOP) in the epilimnion of natu-
ral waters (Bronk
2002
; Zhang et al.
2004
; Kim et al.
2006
; Vähätalo and Järvinen
2007
; Li et al.
2008
). (v) Energy changes (
±
), such as supply (
+
) or consumption
(
−
) of energy because of the photodegradation of DOM, with (
+
) representing the
photoinduced formation of biologically labile compounds and (
−
) the abiotic min-
eralization of DOM (Wetzel
1992
; Tranvik
1992
; Hedges et al.
2000
).
or NO
2
5.2 Ecological Significance of Microbial Degradation
of FDOM
The major changes in FDOM components and organic matter by microbial deg-
radation can be discriminated as (Mostofa et al.
2009b
): (i) Microbial assimila-
tion of organic matter (e.g. algae or phytoplankton) can produce autochthonous
DOM or FDOM at different rates in lake waters, and it can simultaneously pro-
duce nutrients (PO
4
3
−
, NH
4
+
), H
2
O
2
, organic peroxides, and DIC (Ma and Green
2004
; Mostofa and Sakugawa
2009
; Zhang et al.
2009a
; Yamashita and Tanoue
2008
; Palenik and Morel
1988
; Weiss et al.
1991
; Harvey et al.
1995
; Lehmann
et al.
2002
).
(
ii) The fluorescence intensities of fulvic and humic acids are usu-
ally increased under dark incubation. It is suggested that these compounds are
usually recalcitrant to microbial degradation, and microbial effects typically cause
a change in the chemical compositions of aliphatic carbon, which may enhance
the fluorescence intensity (Mostofa et al.
2009a
; Ma and Green
2004
; Moran
et al.
2000
). In contrast the fluorescence of tryptophan-like or protein-like compo-
nents is often decreased under dark incubation, suggesting that tryptophan-like or
protein-like components are labile to microbial degradation (Mostofa et al.
2010
;
Baker and Inverarity
2004
). (iii) Changes in the FDOM components by microbial
degradation under dark incubation induce the release of a variety of microbial
products such as DIC, PO
4
3
−
, NH
4
+
, H
2
O
2
, organic peroxides and so on (Ma and
Green
2004
; Moran et al.
2000
; Mostofa and Sakugawa
2009
; Palenik and Morel
1988
). It is thus suggested that microbial processes can induce important changes
in DOM composition in natural waters. (iv) Extracellular polymeric substances
(EPSs), biologically produced by most bacteria, are composed of a mixture of
polysaccharides, mucopolysaccharide and proteins. EPSs mostly show the Ex/
