Environmental Engineering Reference
In-Depth Information
could favor the occurrence of photosynthesis in natural waters, where H
2
O
2
instead of H
2
O would be involved as reactant in photosynthesis (xCO
2
+
yH
2
O
2(H
2
O)
+
h
υ
→
C
x
(H
2
O)
y
+
O
2
+
energy; and 2H
2
O
2
+
h
υ
→
2H
2
O
+
O
2
)
(Mostofa et al.
2009a
; Komissarov
1994
,
1995
,
2003
). (v) Production of CO
2
and DIC by photoinduced degradation of DOM and particulate organic matter
(POM: ca. algae) can potentially influence carbon cycling and climate change
(Ma and Green
2004
; Salonen and Vähätalo
1994
; Graneli et al.
1998
; Clark et
al.
2004
; Xie et al.
2004
; Borges et al.
2008
; Kujawinski et al.
2009
; Tranvik et
al.
2009
; Omar et al.
2010
; Ballaré et al.
2011
; Zepp et al.
2011
).
1.2 Biogeochemical Functions of DOM for Microbial
Processes in Natural Waters
The major changes in organic materials and DOM by microbial processes can be
listed as follows:
(i) Microbial degradation of vascular plant material is the only anaerobic pro-
cess that, according to physical (temperature, moisture), chemical (redox,
nutrient availability) and microbial (microfloral successional patterns, avail-
ability of microorganisms) factors can diagenetically produce the humic
substances (mostly fulvic and humic acids), proteins, carbohydrates, unidenti-
fied organic substances and nutrients in soil or sediment pore water environ-
ments (Mostofa et al.
2009a
; Conrad
1999
; Lovley
2006
; Wetzel
1992
; Malcolm
1985
; Nakane et al.
1997
; Uchida et al.
1998
,
2000
).
(ii) Microbial respiration or assimilation of POM (ca. algae or phytoplankton) can
produce autochthonous fulvic acid-like substances (C- and M-like) (see the
FDOM chapter for detailed description), various DOM components as well
as nutrients at different rates in aquatic environments (Harvey et al.
1995
;
Mostofa et al.
2009b
; Conrad
1999
; Lovley
2006
; Yamashita and Tanoue
2008
; Fu et al.
2010
; Weiss et al.
1991
; Lehmann et al.
2002
; Zhang et al.
2009
). The microbial origin of these autochthonous organic substances and
nutrients in association with photoinduced production are susceptible to con-
trol the organic carbon and nutrients dynamics in natural waters.
(iii) Microbial processes may generally affect the chemical composition of aliphatic car-
bon (e.g. carbohydrates) in macromolecules such as humic substances (fulvic and
humic acids) of vascular plant origin, or autochthonous fulvic acids of algal or phy-
toplankton origin. Chemical alterations have been observed either experimentally
under dark incubation or in sediment pore waters (Mostofa et al.
2007a
,
b
,
2009b
;
Conrad
1999
; Moran et al.
2000
; Deshmukh et al.
2002
; Li W et al., unpublished
data). The changes in pore-water autochthonous fulvic acid of algal origin can be
identified by the differences in excitation-emission matrix (EEM) spectra and by
an increase with depth of fluorescence intensity in sediment pore waters. Studies
observe that the relative increase in fluorescence intensity of peak C (relative to
