Geoscience Reference
In-Depth Information
determined by
NO
3
k
DNI
k
DNI
−
T
20
K
NO
3
=
K
NO
3
(
20
)θ
(12.84)
+
C
DO
NO
3
is the temperature coefficient for denitrification (about 1.045), and
k
DNI
is the half-saturation DO concentration for denitrification (about 0.1 gO
2
where
θ
m
−
3
).
The last terms on the right-hand side of Eqs. (12.77)-(12.79) account for the organic,
ammonia, and nitrate nitrogen fluxes across the bed surface. Note that to be consis-
tent with the water/bed exchange fluxes in Eq. (12.53) a “-” sign is used in these
terms. This implies a positive value directs from the water column to the benthic
sediment.
·
Phosphorus cycle
Modeling the phosphorus cycle is essentially analogous to the approach used for
the nitrogen cycle. Phosphorus is divided into organic and inorganic forms. In some
models, the organic phosphorus is further partitioned into particulate and dissolved
forms that are separately simulated, and the inorganic phosphorus is partitioned into
dissolved and sorbed forms when sediment sorption is considered. Here, two sin-
gle kinetics equations are introduced for organic phosphorus (OP) and inorganic
phosphorus (orthophosphate, PO
4
) without further partition. Their kinetics are
described by
DC
OP
Dt
−
ω
S
OP
h
OP
h
(
=
K
M
a
PC
f
Phy
,
OP
C
Phy
−
K
OP
C
OP
1
−
f
OP
,
d
)
C
OP
−
(12.85)
DC
PO
4
Dt
S
PO
4
h
=
K
M
a
PC
(
1
−
f
Phy
,
OP
)
C
Phy
+
K
OP
C
OP
−
K
Phy
a
PC
C
Phy
−
(12.86)
where
C
OP
and
C
PO
4
are the concentrations of organic and inorganic phosphorus
(gP
m
−
3
), respectively;
K
OP
is the mineralization rate coefficient of organic phos-
phorus (day
−
1
);
·
f
Phy
,
OP
are the fractions of dead and respired
phytoplankton recycled to the organic and inorganic phosphorus pools, respectively;
f
OP
,
d
is the fraction of the dissolved organic phosphorus;
a
PC
is the phytoplankton
phosphorus-carbon ratio; and
S
OP
and
S
PO
4
are the organic and inorganic phosphorus
fluxes from the sediment bed (gP
f
Phy
,
OP
and 1
−
m
−
2
day
−
1
), respectively.
The terms on the right-hand side of Eq. (12.85) represent the production of organic
phosphorus due to phytoplankton death and respiration, loss due to mineralization,
settling of the particulate organic nitrogen, and exchange at the bed surface, respec-
tively. The terms on the right-hand side of Eq. (12.86) represent the production of
inorganic phosphorus due to phytoplankton death and respiration, gaining due to
mineralization, uptake for phytoplankton growth, and exchange at the bed surface,
respectively.
·
