Environmental Engineering Reference
In-Depth Information
δ
13
C value in the phytoplankton bloom season suggests that phytoplankton pho-
tosynthesis may be limited by CO
2
depletion (Takahashi et al.
1990
). It has been
observed that aqueous CO
2
, [CO
2
]
aq
, determined in freshwater and marine waters
is relatively low (0.13-35 M) in freshwater and relatively higher (5-120 M)
in seawater (Fogel et al.
1992
; Francois et al.
1993
; Yoshioka
1997
; Takahashi
et al.
1990
; Herczeg and Fairbanks
1987
). All aquatic phototrophs are depleted in
δ
13
C relative to dissolved inorganic carbon (DIC), because Rubisco discriminates
against
13
C (Hu et al.
2012
).
The spatial and temporal variability of
δ
13
C values in aquatic organisms
depends on several factors such as isotopic shifts in available inorganic carbon,
resulting from light-induced HCO
3
−
utilization, variation in solar intensity, differ-
ences in water temperature, internal recycling of respiratory CO
2
, photoinduced
generation of DIC from DOM and POM, and dissolution of sedimentary carbonate
(Yoshioka
1997
; Raven et al.
2002
; Jones
1992
; Ma and Green
2004
; Xie et al.
2004
; White et al.
2010
; Liu et al.
2010
; Dreybrodt
1988
; Hemminga and Mateo
1996
; Campbell and Fourqurean
2009
). It is shown that [CO
2
]
aq
concentration is
inversely correlated with the
δ
13
C of organic matter produced by phytoplankton
(Rau et al.
1992
; Freeman and Hayes
1992
). The carbon isotope fractionation of
phytoplankton could be a useful indicator for the assessment of its growth rate
and of CO
2
availability (Fogel et al.
1992
; Takahashi et al.
1991
). Phytoplankton
can actively transport CO
2
by a carbon-concentrating mechanism (CCM) that can
affect its
δ
13
C value (Yoshioka
1997
; Sharkey and Berry
1985
; Bums and Beardall
1987
; Thielmann et al.
1990
). Correspondingly, ß-carboxylation catalysed by
phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase can
affect the
δ
13
C of phytoplankton (Descolas-Gros and Fontugne
1985
; Falkowski
1991
).
To understand the mechanism behind the uptake of CO
2
or HCO
3
−
, a fractionation
equation was developed for plant photosynthesis (O'Leary
1981
; Farquhar et al.
1989
;
Raven et al.
1993
) and phytoplankton photosynthesis (Fogel et al.
1992
; Rau et al.
1992
; Francois et al.
1993
; Jasper and Hayes
1994
; Laws et al.
1995
; Yoshioka
1997
;
Berry
1988
).
5.2.1 Basic Equation for Expressing Photosynthetic Carbon Isotope
Fractionation
The photosynthetic carbon isotope fractionation is initially derived based on the
land C
3
plants (O'Leary
1981
; Farquhar et al.
1989
; Yoshioka
1997
). The photo-
synthetic process for uptake of carbon can be depicted as follows (Yoshioka
1997
)::
k
1
←
k
3
[
CO
2
]
out
[
CO
2
]
in
−→
k
2
organic carbon
(5.9)
where
k
i
is the rate constant for process
i
. Processes 1 and 3 are the diffusive influx
and efflux of CO
2
, respectively, whilst process 2 is the carboxylation step by
