Environmental Engineering Reference
In-Depth Information
3.2.2 Photosynthesis
Photosynthesis is the key process for the formation of organic carbon or OM
(e.g. algae or cyanobacteria, phytoplankton, etc.) through light-stimulated inor-
ganic carbon acquisition in surface waters (Mostofa et al.
2009a
; Komissarov
1994
,
1995
,
2003
; Li et al.
2011
; Li
1994
; Zubkov and Tarran
2008
; Beardall
et al.
2009a
,
b
; Wu and Gao
2009
; Liu et al.
2010
). Photosynthetic organisms are
then able to produce autochthonous DOM via photoinduced respiration (or pho-
toinduced assimilation) and microbial respiration or assimilation in natural waters
(Mostofa et al.
2009b
; Zhang et al.
2009
; Conrad
1999
; Weiss et al.
1991
; Harvey
et al.
1995
; Fu et al.
2010
; Thomas and Lara
1995
; Druon et al.
2010
; Yamashita
et al.
2008
). A new hypothesis on photosynthesis also considers that H
2
O
2
might
be involved in the occurrence of oxygenic photosynthesis in both higher plants
(Komissarov
1994
,
1995
,
2003
; Miller and Moran
1997
) and natural water organ-
isms (Mostofa et al.
2009a
,
b
). Occurrence of photosynthesis in natural waters
includes two facts: the first is the generation of numerous chemical species from
DOM, which may proceed as follows: (i) photoinduced degradation of DOM can
produce many photoproducts, such as H
2
O
2
, CO
2
, DIC, CO, LMW DOM, and
so on in upper surface waters (Mostofa and Sakugawa
2009
; Miller and Zepp
1995
; Miller
1998
; Johannessen and Miller
2001
; Ma and Green
2004
; Xie et al.
2004
; Johannessen et al.
2007
; Salonen and Vähätalo
1994
; Amon and Benner
1996
; Granéli et al.
1996
; Remington et al.
2011
; Zepp et al.
1998
; Cai et al.
1999
;
Gennings et al.
2001
; Clark et al.
2004
; Fichot and Miller
2010
; White et al.
2010
;
Cai
2011
); (ii) microbial degradation of DOM including DON and DOP can pro-
duce compounds such as H
2
O
2
, CO
2
, DIC, PO
4
3
−
, NH
4
+
, CH
4
, LMW DOM and
so on (Mostofa and Sakugawa
2009
; Zhang et al.
2004
; Vähätalo and Järvinen
2007
; Lovley et al.
1996
; Ma and Green
2004
; Palenik and Morel
1988
; Li et al.
2011
; Zinder
1990
; Kotsyurbenko et al.
2001
; Zagarese et al.
2001
; Semiletov
et al.
2007
). Many of these compounds can favor the occurrence of photosynthe-
sis either directly or indirectly and lead to fixation of organic carbon or OM from
inorganic carbon in surface waters (Mostofa et al.
2009a
; Komissarov
1994
,
1995
,
2003
; Miller and Moran
1997
; Li et al.
2011
; Ortega-Retuerta et al.
2009
; Li
1994
;
Zubkov and Tarran
2008
; Beardall et al.
2009a
,
b
; Wu and Gao
2009
; Liu et al.
2010
).
A general scheme for the photoinduced (Eq.
3.1
) and microbial or biological
(Eq.
3.2
) degradation of DOM can be expressed as follows (Mostofa et al.
2009a
,
b
):
DOM
+
h
υ →
H
2
O
2
+
CO
2
+
DIC
+
CO
+
LMW DOM
(3.1)
DOM
+
MICROBES
→
CO
2
+
DIC
+
PO
4
3
−
+
NH
4
+
+
CH
4
+
LMW DOM
(3.2)
The second fact is that H
2
O
2
and CO
2
, produced by either photoinduced or
microbial degradation of DOM and POM can take part to photosynthesis, to form
new OM or carbohydrate-type compounds (Mostofa et al.
2009a
,
b
):
