Environmental Engineering Reference
In-Depth Information
k 1
(Ce) (Ci)
CO 2
k 2
k 3
CO 2
→ Organic C
k 4
F 4
CA
HCO 3 - →HCO 3 -*
Phytoplankton cell
. The δ 13 C of the actively trans-
Fig. 9 Schematic presentation of the active transport of HCO 3
* ) is assumed to be the same as that of HCO 3
ported carbon (HCO 3
in the medium. Data
source Yoshioka ( 1997 )
k 3 Ci
F 4
X =
(5.25)
: The transported carbon has the same δ 13 C value
(2) Active transport of HCO 3
as HCO 3
, as depicted in the scheme shown in (Fig. 9 ). The overall fractiona-
tion equation is substantially different from Eq. ( 5.19 ), although the steady-
state for Ci is denoted by a similar term as Eq. ( 5.16 ), which can be written
as:
(∆ k 1 + 1 )(∆ k 3 + 1 )( 1 X ) + (∆ k 1 + 1 )(∆ k 2 + 1 ) X
(∆ k 3 + 1 )( 1 f ) + (∆ k 1 + 1 )(∆ k 3 + 1 )(∆ k 4 + 1 ) f
α =
(5.23)
dissociation process.
Note that f and X are the same as those in the active transport of CO 2 .
Considering that the second- and third-order terms of Δ k i are negligible, and
Δ k 1 = Δ k 3 , then α can be approximated as follows:
where Δ k 4 denotes the fractionation in the CO 2 —HCO 3
α = 1 + ∆ k 1 ( 1 f ) + (∆ k 2 − ∆ k 1 )( 1 f ) Ci
Ce − ∆ k 4 f
(5.24)
When f = 1, α becomes:
α = 1 + (∆ k 2 − ∆ k 1 ) k 3 Ci
F 4
(5.25)
− ∆ k 4
which implies that the overall fractionation decreases by ( Δ k 1 + Δ k 4 ) when
all carbon derives from the active transport of HCO 3 ( F = 1 ) , compared to
the passive diffusion model (Eq. 5.15 ). It can be deduced from (Eq. 5.24 ) that
all fractionation steps, including overall fractionation would be affected by f .
The difference between (Eqs. 5.19 and 5.24 ) or ( Δ k 1 + Δ k 4 ) corresponds to the
difference in δ 13 C values between CO 2 AND HCO 3 . These equations indicate that
the overall fractionation from [CO 2 ] aq to organic carbon may be less than unity
under some conditions (Yoshioka 1997 ).
From a reanalysis of Hinga's data (Hinga et al. 1994 ) one gets that the active trans-
port of CO 2 for S. costatum can contribute ~ 30-40 % of the total carbon influx. The
relative contribution of active transport can reach 25-35 %, without any change in
CO 2 demand for an uptake of 10 % of the total carbon mediated by β -carboxylation
Search WWH ::




Custom Search