Environmental Engineering Reference
In-Depth Information
and other compounds that are produced either photolytically (photoproducts)
or microbially (microbial products), together with other environmental factors,
may then influence photosynthesis (Mostofa et al.
2009a
,
b
; Komissarov
1994
,
1995
,
2003
):
Planktonic algae smaller than 5
μ
m are major fixers of inorganic carbon in the
ocean (Li
1994
) and dominate the phytoplankton biomass in post-bloom, stratified
oceanic temperate waters (Tarran et al.
2001
). Large and small phytoplankton cells
have a critical and differential growth dependence on inorganic nutrients (Zubkov
and Tarran
2008
). UV-stimulated inorganic carbon acquisition is often observed in
phytoplankton species (Beardall et al.
2009a
,
b
; Wu and Gao
2009
). Regeneration
of autochthonous DOM and nutrients (NO
3
−
−
, PO
4
3
−
and NH
4
+
) occurs
during the photoinduced and microbial assimilation of algae or phytoplankton,and
simultaneously also from the photoinduced degradation of DOM in natural waters
(Mostofa et al.
2009a
,
b
; Fu et al.
2005
,
2010
; Stedmon et al.
2007a
,
b
; Ma and
Green
2004
; Kim et al.
2006
; Li et al.
2008
; Zhang et al.
2009
; Carrillo et al.
2002
; Mallet et al.
1998
; Kopá ˇek et al.
2004
; Lehmann and Bernasconi
2004
).
Regeneration of nutrients significantly occurs in waters with high contents of
DOM, which can control the uptake of nutrients during the photosynthetic pro-
cess. Therefore, nutrients usually do not limit photosynthesis, particularly in
waters with high contents of DOM. Primary production is enhanced significantly
by DOM in the upper 30 m of the water column, where the production increase
upon reduction of damaging UV radiation offsets the effects of attenuation of
photosynthetically active radiation (PAR) (Arrigo and Brown
1996
). At greater
depths, where little UV radiation remains, primary production is often reduced due
to removal of PAR by DOM (Arrigo and Brown
1996
). When CDOM is distrib-
uted homogeneously within the euphotic zone, the depth-integrated daily primary
productivity within the euphotic zone (
∫
z
GPP
ez
) is reduced under most bio-optical
(i.e. solar zenith angle, Chl
a
and DOM absorption, ozone concentration) and pho-
tophysiological (i.e. sensitivity to UV radiation) conditions. In such cases, the pre-
dicted reduction in primary production at depth is greater than the enhancement
of production at the surface (Arrigo and Brown
1996
). The
∫
z
GPP
ez
is decreased
when DOM or phytoplankton is restricted to near-surface waters (
−
30 m) and it
is enhanced when DOM or phytoplankton is restricted to a very shallow surface
layer (
−
10 m) (Arrigo and Brown
1996
). DOM effect on photosynthesis can also
be justified from the observation of high primary productivity of phytoplankton
biomass (Chl
a
) (Fig.
4
a) and from the high photosynthetic carbon fixation rate
(Fig.
4
b, c) in coastal waters (usually with high contents of DOM) compared to
pelagic ones (generally with low contents of DOM) (Li et al.
2011
).
Another issue is the sustained photoinduced and/or microbial production of
compounds such as H
2
O
2
, CO
2
and DIC in DOM-rich waters, which can enhance
primary production (Mostofa and Sakugawa
2009
; Mostofa et al.
2009b
; Malkin
et al.
2008
; Ma and Green
2004
; Meriläinen et al.
2001
; Komatsu et al.
2007
). Algae
are significantly produced in some Chinese lakes during the summer stratification
period, leading to high production of autochthonous DOM and nutrients (Mostofa
et al.
2009b
; Fu et al.
2010
; Li et al.
2008
). Such an effect is the consequence of
, NO
2
