Environmental Engineering Reference
In-Depth Information
Photosynthetic efficiency of phytoplankton decreases as irradiance increases
during the morning, and increases as irradiance declines in the afternoon. These
trends are associated with photoprotective strategies in the antennae of PSII and
photodamage of PSII reaction centers (Zhang et al.
2008
). Conversely, H
2
O
2
usu-
ally shows strong diurnal variation and its concentrations increases gradually from
the morning, reaches a maximum at noon and then gradually decreases in the
afternoon (Mostofa and Sakugawa
2009
). Therefore, high production of H
2
O
2
and
the subsequent HO
•
photogeneration (either direct of photo-Fenton mediated) at
noon is susceptible to damages PSII reaction centers.
In addition, autochthonous DOM can produce relatively high amounts of ROS
that can inhibit primary production. The daily estimated net CO
2
fluxes (due to all
processes) are much smaller than daylight photosynthetic rates (
14
C uptake) and
sometimes go in the opposite direction (Kelly et al.
2001
). This indicates that CO
2
fixation measured by
14
C uptake is largely offset, and sometimes exceeded, by CO
2
production. Allochthonous DOC degradation could account for only a part of this
CO
2
production and the remainder presumably comes from the respiration of pho-
tosynthetically fixed carbon (Kelly et al.
2001
). The average rates of net epilim-
netic CO
2
fixation, or net epilimnetic production (NEP) range from 20 to 60 % of
14
C uptake (Kelly et al.
2001
). This is similar to previous estimates of the relation-
ship between net 24 h and daylight photosynthetic fixation (Berman and Pollingher
1974
). Note that NEP is a
community
parameter, including the respiration of grazers,
sediment bacteria and so on. Therefore, is not the same as the term “net photosynthe-
sis” that refers only to the photosynthesis and respiration of algae (Kelly et al.
2001
).
5.6 Variation in Nutrient Contents
Photosynthesis of organisms is dependent on the contents of nutrients that can
either enhance or decrease its efficiency (Parkhill et al.
2001
; Liu et al.
2007
;
Bybordi
2010
). The effects of nutrients on photosynthesis can be classified in two
ways depending on the types of organisms.
Nutrients Effects on Aquatic Microorganisms
The effect of nutrients on photosynthesis in water may be a stimulation of pri-
mary production (Chl
a
), or not (Yoshiyama and Sharp
2006
; Parkhill et al.
2001
; Smith
2003
; Kaneko et al.
2004
; Sterner et al.
2004
; Huszar et al.
2006
;
Nõges et al.
2008
; McCarthy et al.
2009
; Mohlin and Wulff
2009
; Canfield
1983
; Auclair et al.
1985
; Ferris and Tyler
1985
; Steinberg and Muenster
1985
;
Francko
1986
; Jones et al.
1988
; Lewis
1990
; Salas and Martino
1991
; Cullen
et al.
1992
; Sarnelle et al.
1998
; Brown et al.
2000
; Guildford and Hecky
2000
;
Jones
2000
). Observing the uptake of nutrients during primary production or
algal productivity is a complex issue, because of the many factors involved for
the demand and supply of N and P in water. Such factors can be classified as
